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CHAPTER - I

WATER TECHNOLOGY

Q. Define hardness of water. State the type of hardness of water. OR

Distinguish between temporary (carbonate) and permanent

(noncarbonate) hardness.

Ans: Hardness: Hardness of water is defined which prevent lathering of soap

Temporary Hardness: It is due to the presence of dissolved bi-carbonates

of Ca, Mg and other heavy metals. Presence of bicarbonates causes

alkalinity to water. Temporary hardness can be removed by simple boiling

of water.

Permanent Hardness: It is due to the presence of dissolved chlorides and

sulphates of Ca, Mg and other heavy metals it cannot be removed by simple

boiling, chemical treatment is required to remove the hardness.

Q. Desceribe the different types of impurities present in natural water with

examples.

Ans: Impurities in water may be broadly classified into four categories:

i) Dissolved impurities

ii) Suspended impurities

iii) Dissolved gases &

iv) Organic matter.

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1. Dissolved impurities.

The soluble salt impurities present in water included salts of Ca, Mg, Na in

various soluble salt forms oxides of Mn, Fe, Pb &Ar may also present in

water.

2. Suspended impurities.

Suspended impurities are the dispersion of solid particles. Which can be

removed by filtration or settling.

They are of 2 types:-

Inorganic: It includes clay silica, Oxides of Fe & Mn etc.

Organic: Includes wood pieces. Disintegrated particles of dead animals,

leaf, fishes, Bacteria. Alage, and Protozoa etc.

3. Dissolved gases.

Most water contain dissolved gases such as O2, SO2.NH3&oxides of N all of

which are derived from atmosphere.

4. Organic matter: Organic compounds derived from the decay of

vegetables & animal matter including bacteria, water also gets contaminated

with sewage & human excreted matter etc.

Q. Name the two coagulant substances with chemical formulae.

Ans: Alum: [K2SO4.Al2(SO4)3. 24H2O]

Ferrous sulphate: [FeSO4. 7H2O]

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Q. Write the names of the processes which are used to remove impurities

present in natural water.

Sr.No. IMPURITY PROCESS

1 Suspended Sedimentation

2 Colloidal Sedimentation with coagulation,

filtration

3 Dissolved Ion exchange, Zeolite, Limesoda

4 Biological Sterilization

Q. Name the impurities present in natural water. OR List the common

impurities present in natural water. Give two examples

Ans: 1. Suspended impurities: dust, mud, clay particles

2. Colloidal impurities: fine dust, fine clay particles, fine mud

3. Dissolved impurities: CaCl2, MgSO4, CO2, O2, H2S

4. Biological impurities: Bacteria, Germs, microorganism

Q. Distinguish between hard water and soft water. OR Define hard water

& soft water.

Ans: Hard water: “Water which contains chlorides, sulphates and bicarbonates

of calcium and magnesium called as hard water.” Such water does not

produce lather with soap. Hard water cannot use for boilers or for cooking or

washing purposes.

Soft water: “Water which is free from any salts of calcium and magnesium

is called as soft water”. Soft water easily produces lather with soap and can

be safely used for boilers and for other household and industrial purposes.

Q. Name the salts which are responsible for temporary and permanent

hardness of water with chemical formula.

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Ans: A) Temporary hardness is due to the presence of dissolved “bicarbonates of

calcium and magnesium” i.e. Ca (HCO3)2 & Mg (HCO3)2

B) Permanent hardness is due to the presence of dissolved “chlorides and

sulphates of calcium and magnesium” i.e. CaCl2 & CaSO4, MgCl2 & MgSO4

Q. Write short notes on ‗Units of Hardness‘ of water.

Ans: Units of hardness:

The hardness of water is expressed in terms of parts by weight of calcium

carbonate.

There are three systems to express the hardness of water.

1. Clark‘s degree of hardness: It is defined as the number of parts by

weight of CaCO3 present in 70,000 parts by weight of water

∴ 10 Clark =

1Part by weight of CaCO 3

70,000 parts by wt .of Water

2. French degree of hardness: It is the number of parts by weight of

CaCO3 present in 1,00,000 parts by weight of water.

∴ 10 French =

1Part by weight of CaCO 3

1,00,000 parts by wt .of Wat er

3. Parts per million (ppm): It is the number of parts by weight if CaCO3

present in 10,00,000 parts by weight of water.

∴ 1 PPM = 1Part by weight of CaCO 3

10,00,000 parts by wt .of Water

10 Clark = 1.430 French = 14.3PPM.

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Q. What is meant by boiler corrosion? Name the factors causing corrosion

of boiler.

Ans: Corrosion of boiler can be defined as the decaying of metals by a chemical

or electrochemical reaction with their environment.

Corrosion in boiler is due to following reasons.

1. Dissolved gases

2. Dissolved salt

3. Acidity and alkalinity of water

Q. What are the causes of hardness of water? Explain with chemical

reaction.

Ans: The causes of hardness of water are discussed below

1. The rain water absorbs carbon dioxide from air and also from decaying

plants on soil & it forms carbonic acid

H2 O + CO2 H2CO3

Water Carbonic acid

2. When this water flows over rock containing calcium & magnesium

carbonates.

3. These reacts with carbonic acid present in water to form calcium

bicarbonate and magnesium bicarbonate which are highly soluble in

water.

H2CO3 + CaCO3 Ca(HCO3)2

H2CO3 + MgCO3 Mg (HCO3)2

4. There are chlorides & sulphates of calcium & magnesium present on the

surface layer which also dissolve in water.

5. When this water flow on the earth surface,these salt enter in water.In this

way chlorides, sulphates & bicarbonate of calcium and magnesium are

dissolved in water and making it hard.

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Q. Write the ill (bad) effect of using hard water in following industries. OR

What are the disadvantages of hard water in 1) Paper industry 2)

Dyeing in industry 3) Textile industry 4) Sugar industry.

Ans: Bad effect of using hard water in industries

Paper industry:

During the manufacturing of paper, the material like rosin size is added

to the paper pulp to make the surface of paper smooth & glossy. If hard

water is used then Ca++

& Mg++

ions present in it reacts with the material.

So the paper will not have desired smoothness & glossiness.

If salts of heavy metal like Fe & Mn are present in hard water they make

paper yellowish & dull.

Therefore water used in paper industry must be free from these salts.

Dying industry:

In dyeing industry, colouring of fabrics is done with the help of some

organic as well as inorganic coloring substances.

If hard water is used for dissolving the dyes then calcium & magnesium

salts present in it reacts with die to form unwanted precipitate.

These changes the shades of the dies & unwanted coloures are produced.

Iron produces yellow stains (spots) on clothes

Hence hard water should not be used in dyeing industry.

Textile industry:

If hard water is used in textile industry then a large quantity of soap as

well as water is wasted during washing the yarn because calcium &

magnesium salts do not allow formation of lather with soap.

They react with soap (sodium or potassium salt of fatty acid) to form

curdy precipitate which sticks to the fabric making it weak & brittle. Iron

& manganese present in hard water produces spots ( stains) on fabrics

therefore water used in textile industry should be free from calcium,

magnesium, iron & manganese salts.

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Sugar industry:

If hard & impure water is used in sugar industry for refining of sugar the

impurities like sulphates nitrates, alkali carbonate & bacteria present in it

causes difficulties in the crystallization of sugar. The sugar so formed

may be deliquescent (become watery) & get decomposed during storage.

Q. What are the disadvantages or ill (bad) effect of using hard water in 1)

Washing 2) Cooking 3) Bathing 4) Drinking OR

Why hard water is not suitable for 1) Washing 2) Cooking 3) Bathing 4)

Drinking

Ans: 1.Washing:

Hard water consist of soluble sulphate, chlorides & bicarbonates of calcium

& magnesium

If hard water is used for washing, then the Ca & Mg salts react with soap &

produces curdy precipitate of Ca of Mg salts of fatty acid

In this way large quantity of soap is wasted & the precipitate stick to the

cloth making it weak & brittle.

Secondly if iron is present in hard water it forms spots (stains) on clothes

2. Cooking:

The presence of impurities in water also increases the boiling point of water.

Hence vegetables may not cook well, so more time and more fuel required if

hard water is used.

The life of cooking utensils also decreases due to overheating

Hence hard water should not be used for cooking.

3. Bathing:

If hard water is used for bathing then

Wastage of soap takes place as hard water does not form good lather

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Insoluble residue is formed with soap which is adsorbed on our body, due to

which our skin become dry & dark

4. Drinking: If hard water is used for drinking then impurities in hard water

causes bad effect on digestion process and also kidney stone may formed

due to accumulation of calcium oxalate crystals

Q. Soft water is used as boiler feed water. Give reason

Ans : Hard water consist fo impurities such as dissolved oxygen, dissolved carbon

dioxide, mineral acids, dissolved salts of Ca and Mg which causes corrosion

of boiler. Therefore soft water is sued as boiler feed water

Q. What is boiler corrosion? What are the causes of boiler corrosion?

Explain the causes of boiler corrosion. Write control (preventive)

measures.

Ans: “Boiler corrosion can be defined as the decaying of metals by a chemical or

electro chemical reaction with their environment”

The corrosion in boiler due to following reasons

1. Dissolved gases

2. Dissolved salts

3. Acidity or alkalinity of water

1. Dissolved gases:

Among the dissolved gases oxygen has most corroding effect on boiler

Water contains about 8ml of oxygen per litre at 100C

Dissolve oxygen in presence of water under high temperature attacks the

boiler material

4Fe + 4H2O + 2O2 4Fe (OH)2

4Fe (OH)2 + O2 2 ( Fe 2O3. 2 H2O)

Ferrous hydroxide Rust

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Carbon dioxide when dissolved in water forms carbonic acid

H2O + CO2 H2 CO3

The dissolved bicarbonate of Ca & Mg decomposes & gives CO2

Mg (HCO3)2 Mg CO3 + H2O + CO2

2. Dissolved salts:

If hard water contains chlorides of calcium & magnesium; they get

hydrolyses & produces hydrochloric acid

MgCl2+2H2O Mg (OH)2 + 2HCl

This liberated hydrochloric acid react with iron material of the boiler like a

chain reaction producing hydrochloric acid again & again

Fe + 2HCl FeCl2 + H2

FeCl2 + 2H2O Fe(OH)2 + 2HCl

Therefore, due to presence of small amount of CaCl2 or MgCl2 will cause

corrosion of boiler.

3. Acidity or alkalinity of water:

The corrosion in boiler is more it water is used is acidic. It is less when

water is neutral. Again the corrosion of boiler is greater when water is

alkaline.

Control (prevention) of boiler corrosion

By using proper water treatment procedures.

By degasfication to remove the dissolved gases like oxygen, CO2, etc.,

The dissolved CO2 can be removed by the addition of limewater.

Adding calculated amount of base could neutralize the mineral acids.

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Q. What is caustic embrittlement? How it can be prevented (avoided)?

Ans: This a type of boiler corrosion caused due to alkaline water.

During water softening process small amount of sodium carbonate (Na2CO3)

is added in water. In high pressure boilers, sodium carbonate decomposes to

form sodium hydroxide & carbon dioxide & water becomes alkaline due to

formation of caustic soda (NaOH).

Na2CO3 + H2O NaOH + CO2

This alkaline water goes into the cracks by capillary action. Water

evaporates & dissolved caustic soda is left behind.

The deposition of more & more caustic soda dissolves iron material of the

boiler.

This causes embrittlement (corrosion) of boiler parts, called as caustic

embitterment.

Caustic embrittelment can be avoided by

1. By using sodium phosphate for water softening

2. By adding tannin or lignin additives

3. By adjusting the alkalinity of water (PH 7-9)

Q. Define scales & sludge OR What are scales and sludge in boiler? Write

prevention (control) measures

Scales: The hard and adherent coating formed on inner walls of the boiler is

called as boiler scales. They stick very firmly on to the inner wall surface

and are difficult to remove with chisel and hammer.

Prevention:

Methods of prevention of scales

Internal conditioning method: Internal conditioning methods involve

addition of complexing agents like calogen to boiler feed water. Another

method of internal conditioning method is Phosphate conditioning. In this

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method sodium phosphate is added to boiler feed water which forms non-

sticky Calcium and magnesium Phosphate which can be removed by blow

down operation.

External conditioning method: In external conditioning methods water is

purified either by Zeolite process or by ion-exchange method before being

fed into boilers.

Sludge: When the precipitated matter forms a soft, loose, slimy deposits

inside the boiler which do not stick to the boiler permanently are called

boiler sludge.

Prevention:

a. By using well softended water.

b. By drawing off a portion of concentrated water frequently.

Q. Explain causes of scale & sludge formation in boiler. OR How scale and

sludge formed in boiler?

Ans: The main causes of scale & sludge formation in boiler are

1. Chemical decomposition OR Presence of Ca (HCO3)2 & Mg (HCO3)2

2. Decrease in solubility of salts

1. Chemical decomposition OR Presence of Ca (HCO3)2 & Mg (HCO3)2

If water contains soluble bicarbonate of calcium & magnesium then under

high temperature & pressure inside the boiler, it decomposes to give calcium

carbonate precipitate (insoluble) which forms scales.

This effect is observed in low pressure boiler.

In high pressure boilers CaCO3 forms soluble Ca (OH)2.

Ca (HCO3)2 CaCO3 + H2 O + CO2

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2. Decrease in solubility of salts (How calcium sulphate responsible for

scale formation in boiler)

Salts present in hard water; like CaSO4 & silicates of Ca & Mg formed by

reaction with silica (SiO2) have lower solubility at high temperature. In

superheated water CaSO4 is insoluble in boiler. As the water in boiler starts

heating up, the solubility decreases & excess salts are thrown out of water

forming hard deposits in the form of scales.

Q. Write the disadvantages of scale & sludge formation in boiler OR

Explain the ill (bad) effect of using hard water in boiler unit.

Ans: The disadvantages of scale & sludge formation in boiler are as follow.

Wastage of fuel:

Scales deposited on the inner wall of the boiler are poor conductor of heat.

Hence to get the steady supply of steam; overheating of boiler is needed.

Most of the heat is wasted in heating the scales & in this way there is

wastage of fuel.

It is estimated that for 25mm thick scale, nearly 60% of the fuel is wasted.

Lowering safety of boiler OR Decrease in life of the boiler:

Scales are poor conductor of heat it reduces transfer of heat from boiler to

water.

Therefore overheating of boiler is to be done in order to maintain a constant

supply of steam. This makes the boiler material & boiler tubes soft. This

lowers the safety of boiler.

Danger of explosion:

When scales crack due to uneven expansion of scale & boiler material, the

water comes suddenly in contact with overheated iron plate of boiler

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This causes the formation of a large amount of steam suddenly inside the

boiler

Hence sudden high pressure is developed which may causes explosion of

boiler

Decrease in efficiency: Scales may sometimes deposits in the valves of

condensers of the boiler & choke them. These results in decrease of

efficiency of boiler

Q. Write the principle which is used to soften hard water

Ans: During the process of softening of hard water, the soluble calcium and

magnesium salts are converted into insoluble salts. These insoluble salts can

be removed by filtration and soft water can be obtained

Q. What is priming and foaming? Write causes and control

Ans Priming : It may defined as the violent or rapid boiling of water occurring

in the boiler which results in carrying out of water with steam in the form of

a spray.

When a boiler is producing steam rapidly, some particles of liquid water are

carried along with the steam. This process of wet steam formation is called

priming.

Causes : Priming mainly caused due very high water level. The presence of

large amount of dissolved solids, high steam velocities, sudden increase in

steam production rate. Sudden steam demand which leads to sudden boiling,

presence of excessive foam filling the foam spare, and due to faulty boiler

design.

Prevention (Control) : Priming can be controlled by proper boiler design,

fitting mechanical steam purifier, avoiding rapid change in steam rate,

proper evaporation and adequate heating surfaces, uniform distribution of

fuel and providing anti priming pipes, keeping the water level low and avoid

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sudden steam demands. By efficient softening and filtration of the boiler

feed water.

Foaming: Foaming is the formation of small but stable bubbles above the

surface.

Causes:The main reason for foaming is being presence of fatty acids and

other impurities.

Prevention (Control) : Foaming can be controlled by using anti-foaming

chemicals, removal of concentrated boiler water and replacing it by fresh

feed water. Removing oil from boiler water by adding compounds like

sodium aluminate.

Q. Differentiate between scale & sludge.

Ans:

Q. How water softened by Zeolite process? OR Explain Zeolite OR

Permutit process. OR What is Permutit (Zeolite)? Write principle of

Permutit (Zeolite) Process. Explain the process with diagram. Write

chemical & regeneration reactions involved in it. Write advantages and

limitations

Scale Sludge

1 When the precipitated matter forms a

hard adherent coating on the inner

surface of the boiler is called boiler

scales.

When the precipitated matter forms a

soft, loose, slimy deposits inside the

boiler which do not stick to the boiler

permanently are called boiler sludge.

2 Scales are hard and adherent Sludges are soft

3 It cannot be removed by mechanical

means

Sludges can be removed by mechanical

means

4 Scales are bad conductor of heat Sludges are poor conductor of heat

5 Scales are formed throughout the

metal surface in contact with water

Sludges are formed at comparatively

cooler parts of the boiler

6 Scales lead to bursting or explosion

of metal tube

Sludge lead to check up problems

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Ans: Zeolite: Zeolite are complex of silicates and aluminates of metallic and non

metallic oxides. For softening of water, generally sodium zeolite is used. It

has crystalline structure with a chemical formula.

Na2Al2 Si2O8.6 H2O

It is represented as Na2Z or Na2P

Principle: When zeolite come in contact with hard water, sodium ions in

zeolite are replaced by calcium and magnesium to form insoluble

calcium and magnesium zeolite

Working: When zeolites come in contact with hard water, sodium ions

in zeolites are replaced by calcium and magnesium ions to form insoluble

calcium and magnesium zeolites.

Chemical Reactions:

For temporary hardness

Ca(HCO3)2+ Na2P CaP + 2NaHCO3

Mg(HCO 3)2+Na2P MgP + 2 NaHCO3

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For permanent hardness (Write any two reactions)

CaCl2+ Na2P CaP + 2 NaCl

MgCl2+ Na2P MgP + 2 NaCl

CaSO4+Na2P CaP + Na2SO4

MgSO4 +Na2P MgP + Na2SO4

Regeneration: After some time all the Na+ ions from zeolite (permutit)

completely gets converted into calcium and gets exhausted. At this stage,

supply of hard water is stopped. The exhausted zeolite is regenerated

or reactivated by passing 10% Brine solution( NaCl) through it

Regeneration reaction ( What is the actionof NaCl in regeneration of

Zeolite?)

CaP + 2NaCl Na2P + CaCl2 Brine Solution

MgP + 2 NaCl Na2P + MgCl2

The washings containing CaCl2 and MgCl2 are passed to drain and the

regenerated zeolite is used again. Water softened by zeolite is almost of

zero hardness.

Limitations of Zeolite process:

The capital cost involved in the zeolite process is much high as compared

to other conventional methods like soda- lime process.

If water contains some mineral acids, it cannot be softened by this

process since the acids destroys the softening material, sodium zeolites.

If water contains Fe or Mn salts, the original sodium zeolites are

converted into Fe or Mn zeolites which cannot be regenerated easily.

Advantages of Permutit or Zeolite Process:

Zeolite removes the hardness completely

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It is a clean process

It requires less time for softening

The equipment used is compact and occupying small space

Q. How water softened by zeolite process?Explain Ion Exchange or

Demineralization or Deionisation process with diagram.(Only process

and Diagram). Write chemical & regeneration reactions involved in it.

Write advantages and limitations.

Ans: Process: It consists of three cylindrical towers. First tower consists of cation

exchanger (RH2) and second tower consists of anion and alkali tanks for

regeneration of the exhausted resins.

Third tower is a degasifier.

Hard water is first passed through the cation exchanger. It removes all the

cations like Ca++

, Mg2+

and releases H+

ions.

Chemical reactions

RH2 + CaCl2

RCa + 2HCl

RH2 + MgSO4

RMg + H2 SO4

Thus water is free from cations but it is acidic.

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The acidic water is then passed through anion exchanger where acids are

converted into water.

Chemical reactions

R‟-(OH)2 + 2HCl RCl2+2H2O

R‟-(OH)2 + H2SO4 R- SO4 + 2H2O

3. Thus water is free from all cations and anions. Finally water is made free

from dissolved gases like CO2, O2 by passing it through third tower of

degsifier.

Regeneration: When the cation exchanger resins get exhausted, they are

regenerated by passing the solution of dill. HCl or H2SO4 through first

tower.

R-Ca + 2HCl RH2 + CaCl2

R-Mg + H2SO4 RH2+ MgSO4

The washings containing CaCl2 , MgCl2 , CaSO4 , MgSO4 etc. is passed to

drain.

When the anion exchanger resin get exhausted, they are regenerated by

passing the solution of dil. NaOH or KOH through second tower.

RCl2 + 2NaOH R(OH)2 + 2NaCl

RSO 4 + 2NaOH R(OH)2 + Na2SO4

The washings containing NaCl, Na2SO4 etc. is also passed to drain.

The regenerated resins are then used again.

Advantages:

This process can be used for purifying highly acidic or alkaline water

Water of zero hardness is obtained

Small space occupying equipment and portable

Water totally free from any ionic impurity is obtained

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Treated water contains negligible amount of total dissolved solid i.e. up

to 5 mg/lit

Limitations:

The equipment is costly and more expensive chemicals are needed

Turbidity may clog the pores of resins and reduce the output of process

Method cannot be used for getting deionized water on large scale

Q. Define potable water. Mention its requirements (parameters/standards).

Ans: “Water which is fit for human consumption and safe to drink is known as

drinking water or potable water.”

Requirement (Characteristics/Parameters/standards) for potable water:

It should be colourless, odourless and clear

It should be totally free from disease producing microorganisms like

germs and bacteria

Water should be soft and pleasant in tasteThe turbidity of water should be

less than 10 ppm

If water has a colour then it should be less than 20ppm

If water dissolve any solid then it should be less than 500ppm

It should be free from dissolved gases like hydrogen sulphate

Q. Explain the terms: 1) Screening 2) Sedimentation 3) Coagulation

Ans: Screening:

“Screening is the process of removing floating materials from water.” To

remove the floating matter, mainly this method is used.

The water is allowed to pass through screens having a large number of

pores. Thus, only floating material remains on the screen.

Sedimentation:“Sedimentation is the process of removing suspended

impurities by allowing the water to stay undisturbed for some time in large

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tanks when most of the suspended particles settle down due to the force of

gravity.”

The process of sedimentation is generally carried out in continuous flow

type tanks in which water flows continuously in a horizontal or vertical

direction at a slow and uniform speed. Due to gravitational force, the

suspended particles get settled down at the bottom of the tank, form where

they can be removed periodically. Sediment water is taken out continuously.

Coagulation:

“Coagulation is the process of removing colloidal (or fine size) particles

from water by the addition of certain chemicals known as coagulants before

sedimentation”. This process is usually carried out along with

sedimentation.

The commonly used coagulants are the salts of iron and aluminium e.g. alum

[K2SO4. Al2(SO4)3. 24H2O], ferrous sulphate (FeSO4.7H2O) etc.

These coagulants react with bicarbonates present in water, and form bulky

gelatinous precipitate called flock. As these flocks descend through water,

they absorb or catch suspended fine particles from water and forming bigger

flocks, which settle down quickly.

The addition of coagulants to water also removes colour, odour and

improves its taste.

Al2(SO4)3 + 3 Ca (HCO3)2 2Al (OH)3 + 3CaSO4 + 6CO2 (Coagulant) Calcium (Bulky gelatinous flock)

Bicarbonate

FeSO4 + Mg(HCO3)2 Fe (OH)2 + MgSO4 + 2CO2 (Coagulant) Magnesium (Ferrous Hydroxide)

Bicarbonate

4 Fe (OH)2 + 2H2O + O2 4 Fe (OH)3 (Dissolved oxygen) Ferric hydroxide

(Heavy flock)

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Q. What is desalination? How is it done by reverse osmosis? OR State the

principle of reverse osmosis. Explain the process of desalination of sea

water by reverse osmosis.

Ans: Desalination : the process of removing common salt from water is called as

desalination

Reverse osmosis is a technique used for the purification of sea water in to

drinking water.

Principle of reverse osmosis: This method is based on the principle that if a

hydrostatic pressure greater than the osmotic pressure is applied on the more

concentrated solution side then the solvent molecules begin to move through

a semi permeable membrane in a direction opposite to that predicated by

natural osmosis. That is the solvent molecules begin to move from the

concentrated solution side to diluted solution and hence the name reverse

osmosis.

Process:

In this method hard water and soft water are taken in two different chambers

separated by a semi permeable membrane.

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When a hydrostatic pressure greater than the osmotic pressure is applied on

the hard waterside, the water molecules move from hard waterside to soft

waterside leaving the impurities on the membrane due to reverse osmosis.

Thus hard water is converted to soft water by super filtration of hyepr

filtration.

The membrane consists of a polymeric material film made of proper

porosity, from materials like cellulose acetate, acrylics, polyamides,

barmaids etc.

Q. How hardness determined by EDTA method? OR Explain EDTA

titration method for determination of total and permanent hardness of

water.(Write only procedure)

Ans: Chemicals required:

1. Standard hard water

2. EDTA solution (0.01M)

3. EBT indicator

4. Ammonia buffer

Principle:

EDTA stands for Ethylene Diamine Tetra Acetic acid. As it is insoluble in

water, we use its disodium salt.

Structure of EDTA:

By nature, Eriochrome Black T indicator is blue in colour. When EBT

indicator is added to water sample, it forms wine red coloured unstable

Ca-Mg-EBT complex. This reaction is carried out under a basic PH of 8-10

using ammonia buffers.

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Ca2+

/Mg2+

in water + EBT [Ca/Mg-EBT] unstable wine red complex.

When EDTA is titrated against the complex, EDTA replaces all the

EBT and forms a stable Ca/Mg-EDTA complex. The liberated EBT

indicates the end point as steel blue.

[Ca/Mg-EBT] + EDTA [Ca/Mg – EDTA] + EBT

(Wine red/unstable) (Stable) (Steel blue)

So, the end point is the colour change from wine red to steel blue.

Procedure:

Determination of total hardness:

Pipette out 50 ml of the given hard water sample into 250 ml conical flask.

Add 5 ml of buffer solution to increase the pH to about 10.

Add 3-4 drops of Eriochrome Black- T indicator.

The solution turns wine red.

Titrate the hard water sample slowly with 0.01M EDTA until the colour

changes to blue (end point).

Note down the volume of EDTA used up at end point.

Determination of permanent hardness:

50ml hard water sample is boiled for about 15 to 20 minutes.

Then filtrate is diluted with distilled water to make 50 ml.

Add 5ml of buffer solution to increase the pH to about 10.

Add 3-4 drops of Eriochrome Black-T indicator.

The solution turns wine red.

Titrate the boiled hard water sample slowly with 0.01M EDTA until the

colour changes to blue (end point).

Note down the volume of EDTA used up at end point.

Using the above data, total and permanent hardness can be calculated.

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Q. What is meant by Alkalinity? Give any two chemicals (substances)

responsible for it. Give importance (significance) of alkalinity

Ans: Alkalinity in water arises due to the substances that can cause the formation

of hydroxy1 ions & in turn can react with strong acid.

Substances that cause the alkalinity in water are of three types.

Hydroxides ( NaOH , Ca(OH)2 )

Carbonates (Na2CO3, CaCO3)

Bicarbonates ( NaHCO3, Ca (HCO3)2 )

Importance of alkalinity: Highly alkaline water are usually disagreeable

and upper limits to phenolphthalein alkalinity and total alkalinity are required

to specified. Alkaline water used in boilers for steam generation may cause to

precipitate of sludges, deposition of scale and causes caustic embrittlement. A

knowledge of the kinds of alkalinity present in water and their magnitude is

important in calculating the amounts of lime [Ca(OH)2] and soda [Na2(CO)3]

needed for water softening. Use of different fertilizers in agriculture is

dictated by alkalinity of water

Q. Explain the method of determining the Alkalinity in water

Ans: Principle: Alkalinity is determined by titrating a known volume of water

sample with indicator against a strong acid.

Two types of alkalinity can be evaluated based on the indicator used.

Alkalinity when methyl orange is used.

When methyl orange is used as indicator, only after all the three reactions,

the color change observed & that indicate the end point.

25

Total alkalinity = Alkalinity due to hydroxyls + Alkalinity due to Carbonates

+ Alkalinity due to bicarbonates.

When phenolphthalein is used, only after the two reactions (I&II) before the

III reaction occur, the color change observed & that indicate the end point.

Alkalinity with phenolphthalein = Alkalinity due to hydroxyls + ½

Alkalinity due to Carbonates.

Procedure:

Part – I

Pipette out 100ml water sample into a clean conical flask.

Add two drops of Methyl Orange indicatorin it.

Titrate against standard (say 0.02N) HCl till the color of the solution

changes sharply from yellow to orange. Let the volume of HCl consumed be

Xml.

Part - II

To another 100ml sample of water, add two drops of phenolphthalein.

Titrate against standard (say 0.02N) HCl till the color of the solution

changes sharply from pink to colorless.

Let the volume of HCl consumed be Yml.

Calculations

a) Alkalinity due to methyl orange.

1000ml of 1N HCl is equivalent to 50 g Of CaCO3 (50 being the

equivalent weight of CaCO3).

1ml of 1 N HCl is equivalent to 50/1000 g of CaCO3

Xml of 0.02 N HCl is equivalent to 50X x 0.02/1000 g CaCO3

26

10 6ml of water sample contains 50X x 0. 02 x 10

6/1000 x100 g of

CaCO3 = 10X g of CaCO3

i.e. Alkalinity of methyl orange = 10X ppm of CaCO3 equivalent

b) Alkalinity due to Phenolphthalein.

This is also in similar way that is

Alkalinity of Phenolphthalein is 50 x Y x 0.0 2 x 106 / 1000 x 100

= 10Y ppm CaCO3

Q. Explain Mohr‘s method of determining the Chloride content in water

Ans : Procedure: Transfer 100cm3 of water sample into a clean conical flask.

Add about 1 cm3 of K2CrO4 indicator solution &titrate against standard (say

0.02N) AgNO3 solution until a reddish brown color persists in the white

precipitate. Record the volume of AgNO3 consumed (Let „a‟ cm3). Perform a

blank titration taking 100 cm3

of distilled water. The volume of AgNO3

consumed Let „b‟ cm3.

Calculation:

Volume of AgNO3 required for chlorine estimation = (a - b) cm3 = V

1000 ml of 1 N AgNO3 = 35.45g/𝐶𝑙−

1 ml of 1N AgNO3 = 0.03545 g/𝐶𝑙−

V ml of 0.02 N AgNO3 = 0.03545X V X 0.02 g/𝐶𝑙−

𝐶𝑙− content in the sample = 0.03545 ×𝑉×0.02

100𝑔𝑟𝑎𝑚𝑠/𝐶𝑙−

𝐶𝑙−content in the sample =0.03545 ×𝑉×0.02 ×1000

100𝑚𝑔/𝐶𝑙−

27

Q. Explain Electrodialysis method for purification of brackish water.

OR

What is brackish water? How is it purified by electrodialysis?

Ans : Brackish Water : The water containing dissolved salts with a peculiar salty

taste, is called as brackish water.

Principle: Electrodialysis is a method in which the +ve and –ve ions are

pulled out of the salt water through an ion selective membrane by passing

direct current.

Method: Sea water is taken in a three chambered vessel where the end

compartments function as the cathodic and anodic compartments. On

passing a direct current, + ve sodium ions start moving toward the cathode

and the - vely charged chloride ions begin to move towards the anode

through the membrane. Hence the concentration of NaCl decreases in the

central compartment while the concentration of ions increases in the two

side compartments. Thus the water in the central compartment becomes

desalinated and can be removed periodically. The concentrated water in the

side compartments is also replaced periodically with fresh water.

28

INSTRUMENTAL METHODS OF ANALYSIS

Q. What are Instrumental methods of analysis ?

Ans : It is one of the quantitative analysis methods of a compound. An instruments

is used for chemical analysis, converts the property of substance which is

under investigation in to form that can be readily measured. The measured

quantity is related to the quantity or quality of the sample.

Q. What are the Advantages of Instrumental Methods?

Ans : Advantages of Instrumental Methods :

1. Even complex samples can be handled easily.

2. These methods are faster than chemical methods.

3. These methods requires only small quantities of the sample.

4. Easy when a large number of samples have to be analyzed.

5. These methods are accurate

6. The analytical process can be automated.

7. High sensitivity is obtained.

Limitations of Instrumental Methods:

1. The equipments are generally expensive.

2. Specialized training is required to operate the instruments.

3. An initial or continuous calibration and standardization is required.

4. The concentration range is limited.

5. Sizable space is required.

29

Q. What is the principle of PH -Metry? Write advantages, disadvantages

and applications of PH-metry.

Principal: PH is a measure of the hydrogen ion activity of a solution, which

defines the degree of acidity or alkalinity of the solution.

Advantages:

Accuracy- It measures more accurately than test strip or ther method of

pH measurement.

Ease of use – Using pH indicator is messier that pH meter.

Precision-pH meters are more precise and can measure down the 0.01th

of pH unit. Accuracy of strip is less.

Disadvantages:

PH meter need to be calibrated at some frequency.

More expensive than pH paper.

Probe has to be cleaned well after ever use to get accurate reading next

time.

Applications:

Used to test water for its level of acidity versus base or alkalinity.

In pharmaceutical industries, PH

meters are designed to cater the

requirement of analytical labs. Used to test the level of concentration of

acids, alkalines and unwanted particles in medicinal fluids of liquids.

It is used in agriculture to tell the alkalinity of soil.

Used in food industries to test butter and yogurt.

Used in wine industries.

30

Q. What is principle of conductometry? Write advantages, disadvantages

and applications of conductometry

Ans : Principle: Conductivity is a parameter used to measure the ionic

concentration and activity of solution.

Advantages:

They are useful incase of coloured solutions.

They give more accurate equivalence point.

It is also useful for dilute solutions.

In this method in no special care is necessary near the end point as it is

determined graphically.

Disadvantages:

It is less satisfactory and less accurate with increasing total electrolyte

concentration.

This method is applicable to all types of volumetric applications but for

oxidation reduction system it is limited.

Applications:

To test the conductivity of aluminium copper and other non- ferrous

magnetic metal in processing industry.

In aerospace and automotive industry to monitor the process of heat

treatment strength and hardness of aluminium alloy to test the purity

grade of materials.

It is useful for determination of atmospheric SO2.

It is used in measuring the salinity of sea water in oceanographic work.

To determine basicity of organic acids ionic product of water

31

Q. What is principle of colorimetry? Write advantages, disadvantages and

applications of colorimetry?

Principal: It is instrument used for measuring absorption in visible region

and to characterize coloured sample.

Advantages:

It is simple instrument and requires little maintains.

Sample testing in laboratory can minute or hours whereas calorimeter can

take minutes or even seconds to tests.

Material cost is low even if material is costly it is frequency possible to

use dilution in solvent such as water

Disadvantages:

Cost of colorimeter is high

Unable to measure transparent samples.

Cannot differentiate between colour and appearance.

Applications:

For determination of structure of organic compounds,inorganic

compounds and inorganic complexes.

In Biology colorimeter is used to monitor the growth of bacterial or

yeast culture. As culture grows, the medium in which it is growing

becomes increasingly cloudy and absorbs more light.

Used to test concentration of plant.

Used to test concentration of plant nutrients in soil or to test hemoglobin

of blood

32

Used to indentify substandard and counter drugs.

Used in food industry and in manufacture of points and textiles.

Q. What is principle of potentiometry? Write advantages, disadvantages

and applications of potentiometry

Ans : Principal :A titration in which the equivalence or end point of a reaction is

determined with the help of the measurements of the potentials of the

reaction mixture is known as the potentiometric titrations.

. Advantages:

The method can be used with coloured solutions (Turbid, flurocent).

The method can be used for the analysis of dilute solution with high

degree of accuracy.

The method can be used for titration weak acid against weak bases

Different titration is possible.

There is no need of indicator in Redox titrations.

Disadvantages:

It is laboures, involves lot of time and large number of observation are

required to detect the equivalent point.

Applications:

In case of Acid titration all the types of titration can be carried

potentiometrically.

The system can be used for individual mono basic acid, weak and

strong versus base.

Preciptation titration can be carried out with the help of potentiometer.

33

CHAPTER –II

CHEMICAL ENERGY SOURCES

Q. Define fuel. Give the classification of fuel with example. OR How fuels

are classified?

Ans: “A fuel can be defined as any combustible substance which during

combustion gives large amount of heat energy.”

E.G. Wood, coal, kerosene, diesel, Petrol, coal gas etc.

The fuels are classified into two types:

1. Depending on their occurance

2. Based on their physical state

According to the first classification; the fuels classified into two classes

A) Natural (primary) fuel

B) Artificial (secondary) fuel

A) Natural (primary) fuel:

The fuel which are found naturally as wood, coal, petroleum & natural

gas are called as natural (primary) fuel.

B) Artificial (secondary) fuel:

The fuel which are prepared from natural (primary) fuels, like coke,

charcoal; petrol, diesel L.P.G, producer gas are called as artificial

(secondary) fuel

According to second classification fuels are classified into

1. Solid fuel Ex. Wood ,coal, peat, anthracite

2. Liquid fuel Ex. Crude oil

3. Gaseous fuels. Ex. Natural gas (Marsh gas)

34

Q. Define ignition temperature

Ans: “The minimum temperature at which active combustion of fuel takes place

when the firing is once started is called as ignition temperature”. In other

words, Ignition temperature is the temperature at which fuel starts burning. It

is also known as ignition point.

Q. Define calorific value.

Ans: “It is defined as the total amount of heat produced by the complete

combustion of unit mass of solid fuel or liquid fuel or unit volume of gaseous

fuel in presence of air or oxygen.” OR

“It is also defined as the amount of heat liberated when a unit mass of fuel is

burnt completely in presence of air or oxygen.”

It is the most important property of a fuel which decides the quality of a fuel

Q. Mention the SI units of calorific value

Ans: In SI system the units of calorific value for solid fuels are expressed in J/Kg

and for gaseous and liquid fules are expressed in J/m3.

Q. Define types of Calorific value

Ans : There are two types of calorific value

1. Higher calorific value. (HCV) or gross calorific value . (GCV)

2. Lower calorific value. (LCV) or Net calorific value (NCV)

1. HCV: It is the amount of heat liberated when a unit mass of fuels burnt

completely in the presence of air or oxygen and the products of

combustion are cooled to room temperature. Here it includes the heat

liberated during combustion and the latent heat of steam. Hence its value

is always higher than lower calorific value.

2. LCV: It is amount of heat liberated when a unit mass of fuel is burnt

completely in the presence of air or oxygen and the product of

combustion are let off completely into air. It does not include the latent

heat of steam. Therefore it is always lesser than HCV.

35

Q. Give relation between HCV and LCV

Ans : Relation between HCV and LCV

LCV = HCV – Latent heat of steam

LCV = HCV – mass of hydrogen x 9 x latent heat of steam

Q. Gross calorific value is higher than net calorific value. Give reason

Ans: Gross calorific value includes the heat liberated during combustion and the

latent heat of steam but net calorific value does not include the latent heat of

steam. Therefore GCV is higher than NCV

Q. Mention the units of calorific value

Ans: The units of calorific value for solid fuels and liquid fuels are expressed in

Kcal/Kg and for gaseous fuel in Kcal/m3

Q. Write the characteristics (Properties) of good fuel.

Ans: A good fuel has following characteristics

1. It should have moderate ignition temperature

2. It should have high calorific value

3. It should posses moderate velocity of combustion

4. Its moisture content should be low

5. It should have low content of non combustible matter

6. It should be available in bulk at low cost

7. It should be easy to store & transport

8. It should be burn in air with efficiency

9. It should not undergo spontaneous combustion

10. It‟s product of combustion should not be harmful

36

Q. State the advantages & disadvantages of solid fuels.

Ans: Advantages of solid fuel are as follow

1. They are easy to transport

2. They are convenient (easy) to store without any risk of burning

3. They are having moderate ignition temperature

4. Their cost of production is low

Disadvantages of solid fuel are as follow

1. A large amount of ash is formed during burning

2. Their thermal efficiency is low

E.g. A large amount of heat is wasted during combustion

3. Their cost of handling is high

4. Their calorific value is lower than liquid or gaseous fuel

Q. State the advantages & disadvantages of liquid fuel.

Ans: Advantages of liquid fuel are as follow

1. They have high calorific value than solid fuel

2. They burn without forming ash & clinkers

3. They have moderate ignition temperature

4. They are easy to transport through pipes

5. They have better thermal efficiency

Disadvantage of liquid fuel are as follow

1. The cost of liquid fuel is relatively higher than solid fuels

2. Liquid fuels require costly special storage tanks for storages

3. They give bad odour while burning

4. A specially designed burners are required for liquid fuels

5. As they have low ignition temperature care should be taken while storing

& transport. E.g. there is a greater risk of fire hazard in case of petrol

37

Q. State the advantages & disadvantages of gaseous fuels.

Ans: The advantages of gaseous fuel are as follow

1. They have higher calorific value as compared to solid & liquid fuels

2. They are clean in use of economic in labour

3. Their combustion can be easily controlled by the use of regulator

4. They burn without smoke & are ash less

5. They have high thermal efficiency

Disadvantages of gaseous fuel are as follow

1. They are more costly as compared to solid & liquid fuels

2. They have very low ignition temperature & therefore more dangerous in

storing & transporting

3. They require large storage tanks, hence storage become costly

4. They are highly inflammable, so the chances of fire hazards are very high

Q. What is proximate analysis of coal? Describe proximate analysis of coal

for

1) Moisture ( % of moisture)

2) Volatile matter (% of volatile matter)

3) Ash (% of ash)

4) Fixed carbon (% of fixed carbon)

Ans: Proximate analysis:

“The analysis of coal sample in which the moisture, volatile matter, ash

& fixed carbon content are found is known as proximate analysis.”

1. Determination of moisture ( % of moisture)

It involves following steps

1. Firstly about 1gm of fine powdered air-dried coal sample is weighed in a

crucible

2. Then the crucible is placed in an electric hot oven for 1 hr at 1050C

3. The crucible is taken out from the oven & cooled in desiccators &

weighed (w1 gm)

Then the loss in weight (w-w1) is reported as moisture

38

Percentage (%)

of moisture =

Loss in weight (w-w1) X 100

Weight of coal

Sample (w)

2. Determination of volatile matter (% of volatile matter)

It involves following steps

1. The dried sample of coal which is left in the crucible is covered with a lid

2. The crucible is then placed in an electric furnace at 9250C for 7 minutes

3. Then the crucible is taken out from electric furnace (muffle furnace) &

then it is cooled in desiccator & weighed ( without lid)

4. From the known weight of volatile matter removed from the coal, its

percentage can be calculated

Percentage (%) =

of volatile matter

Loss in weight X 100

Weight of coal sample

3. Determination of Ash ( % of ash)

It involves following steps

1. The coal sample which is free from moisture & volatile matter is heated

without lid at 7500C in an electric furnace (muffle furnace) for half an

hour

2. Due to this the coal in the crucible gets burnt

3. The ash left in the crucible is then cooled & weighed

4. Cooling & weighing is repeated till a constant weight of ash is obtained

% of ash = Weight of ash X 100

Weight of coal sample

4. Fixed Carbon: the fixed carbon in coal is determined by using the

following equation

Fixed carbon = 100 - (% of moisture + % of volatile matter + % of ash)

39

Q. Write the significance (importance) of proximate analysis. OR Give

significance of moisture, volatile matter, ash & fixed carbon.

Ans:

A) Significance of moisture:

1. Moisture gets evaporated during combustion of coal by taking away

some heat in the form of latent heat of evaporation. Therefore, moisture

reduces the effective calorific value of coal

2. It increases the weight of the coal and as well as its transportation

charges. Hence, lesser the moisture content, betters the quality of coal as

a fuel

B) Significance volatile matter:

1. A high volatile matter containing coal burns with a long and smoky flame

and has low calorific value. So higher volatile matter content in coal is

undesirable

2. Hence lesser the volatile matter, better the quality of the coal as a fuel

C) Significance of ash:

1. Ash is non-combustible, useless matter which reduces the calorific value

of coal

2. It increases the cost involved in ash disposal

3. It causes the difficulties to the flow of air required for burning, thereby

decreasing the efficiency

4. Hence, lower the ash content, better the quality of coal

D) Significance of fixed carbon:

1. Carbon in the coal is the burning matter and produces heat

2. Higher the percentage of fixed carbon, greater is the calorific value

40

Q. Differentiate between Solid Fuel, Liquid Fuel and Gaseous Fuel

Ans :

Characteristic

property

Solid fuel Liquid fuel Gaseous fuel

1. Example Coal Crude oil Natural gas, coal

gas

2. Cost Cheap Costlier than solid fuel Costly

3. Storage Easy to store Closed container

should be used

Storage space

required is huge

and should be

lead proof

4. Fire

hazards

Less More Very high, since

these fuels are

highly

inflammable

5. Combustion

rate

Slow process Fast process Very rapid and

efficient

6. Combustion

control

(flame)

Cannot be controlled Can be controlled or

stopped when

necessary

Controlled by

regulating the

supply of air

7. Handling

cost

High, since labor is

required during

storage and

transportation

Low, since the fuel can

be transported through

pipes

Low, since the

fuel can be

transported

through pipes

8. Ash Ash is produced and

their disposals also

possess problems

No problem of ash No problem of

ash

9. Thermal

efficiency

Least High Highest

10. Calorific

value

Least High Highest

11. Use in IC

engine

Can‟t be used Can be used Can be used

41

Q. Give the classification of coal/solid fuel

Ans : Coal has been classified in several ways. The most common method

of classification is on the basis of rank.

Peat: It is the first stage of formation of coal from wood. It is brown, fibrous

jelly-like mass. It contains 80-90% moisture. The composition of peat is

C = 57 %; H = 6 %; O = 35 % Ash = 2.5 %. The calorific value of peat is

5400kcal/kg. it is a low- grade fuel due to high water content. It is used as a

fertilizer and packing material.

Lignite: Lignite is immature form of coal. It contains 20 - 60% moisture.

Air-dried lignite contains C = 60-70 % O = 20%. It burns with a long smoky

flame. The calorific vale of lignite is 6500 - 7100 kcal/kg.

Bituminous coal: It is a high quality fuel. Its moisture content is 4%. Its

composition is C = 83% O = 10% H = 5% and N = 2%. Its calorific value is

8500 kcal/kg.

Anthracite Coal: These coals have very low volatile matter, ash & moisture

it is the superior form (Highest Rank) of coal. It contains C = 92-98%, O =

3%, H = 3% and N = 0.7%. It burns without smoke. It‟s calorific value is

8700/kcal/kg.

Q. Whate is ultimate analysins of coal? Explain the determination of the

following constituents present in coal.

1. Carbon & Hydrogen 2. Nitrogen 3. sulphur 4. Oxygen

Ans : Ultimate analysis : This is the elemental analysis and often called as

qualitative analysis of coal. This analysis involves the determination of

carbon and hydrogen, nitrogen sulhur and oxygen.

1. Carbon and Hydrogen : About 1 to 2 gam of accurately weighed coal

sample is burnt in a current of oxygen in a combustion apparatus. C and

H of the coal are converted into CO2 and H2O respectivley. The gaseous

products fo combustion ae absorbed respectively in KOH and CaCl2

tubes of known weights. The increases in weights of these are then

determined

42

C + O2 CO2

2KOH + CO2 K2CO3 + H2O

H2 + ½ O2 H2O

CaCl2 + 7H2O CaCl2.7H2O

𝑃𝑒𝑟𝑐𝑒𝑛𝑡𝑎𝑔𝑒 𝑜𝑓 𝐶 =𝑖𝑛𝑐𝑟𝑒𝑎𝑠𝑒 𝑖𝑛 𝑤𝑒𝑖𝑔𝑕𝑡 𝑜𝑓 𝐾𝑂𝐻 𝑡𝑢𝑏𝑒 × 12 × 100

𝑊𝑒𝑖𝑔𝑕𝑡 𝑜𝑓 𝐶𝑜𝑎𝑙 𝑠𝑎𝑚𝑝𝑙𝑒 𝑡𝑎𝑘𝑒𝑛 × 44

𝑎𝑛𝑑 𝑃𝑒𝑟𝑐𝑒𝑛𝑡𝑎𝑔𝑒 𝑜𝑓 𝐻 =𝑖𝑛𝑐𝑟𝑒𝑎𝑠𝑒 𝑖𝑛 𝑤𝑒𝑖𝑔 𝑕𝑡 𝑜𝑓 𝐶𝑎𝐶𝑙2 𝑡𝑢𝑏𝑒 ×2×100

𝑊𝑒𝑖𝑔𝑕𝑡 𝑜𝑓 𝐶𝑜𝑎𝑙 𝑠𝑎𝑚𝑝𝑙𝑒 𝑡𝑎𝑘𝑒𝑛 ×18

2. Nitrogen: About 1 gram of accurately weighed powdered coal is heated

with concentrated H2SO4 along with K2SO4 (catalyst) in a long necked

Kjeldahl‟s flask. After the solution becomes clear, it is treated with

excess of KOH and the liberated ammonia is distilled over and absorbed

in a known volume of standard acid solution. The unused acid is then

determined by back titration with standard NaOH solution. From the

volume of acid used by ammonia liberated, the percentage of N in coal is

calculated as follows

𝑃𝑒𝑟𝑐𝑒𝑛𝑡𝑎𝑔𝑒 𝑜𝑓 𝑁 =𝑉𝑜𝑙𝑢𝑚𝑒 𝑎𝑐𝑖𝑑 × 𝑁𝑜𝑟𝑚𝑎𝑙𝑖𝑡𝑦 𝑜𝑓 𝑎𝑐𝑖𝑑 × 1.4

𝑤𝑒𝑖𝑔𝑕𝑡 𝑜𝑓 𝑐𝑜𝑎𝑙 𝑡𝑎𝑘𝑒𝑛

3. Sulphur : Sulphur is determined from the washings obtained from the

known mass of coal, used in bomb calorimeter for determination of a

calorific value. During this determination, S is converted in to Sulphate.

The washings ae treated with Barium chloride solution, when Barium

sulphate is precipitated. This precipitate is filtrated, washed and heated to

constant weight.

43

𝑃𝑒𝑟𝑐𝑒𝑛𝑡𝑎𝑔𝑒 𝑜𝑓 𝑆𝑢𝑙𝑝𝑕𝑢𝑟 =𝑊𝑒𝑖𝑔𝑕𝑡 𝑜𝑓 𝐵𝑎𝑆𝑂4 𝑜𝑏𝑡𝑎𝑖𝑛𝑒𝑑 ×32×100

𝑤𝑒𝑖𝑔 𝑕𝑡 𝑜𝑓 𝑐𝑜𝑎𝑙 𝑠𝑎𝑚𝑝𝑙𝑒 𝑡𝑎𝑘𝑒𝑛 𝑖𝑛 𝑏𝑜𝑚𝑏 ×233

4. Ash : the residual coal taken in the crucible and then heated without lid

in a muffle furnace at 700 +- 50oC for ½ hour. The crucible is then taken

out, cooled first in air, then in desiccators and weighed. Hearing, cooling

and weighing is repeated, till a constant weight is obtained. The residue is

reported as ash on percentage basis.

𝑃𝑒𝑟𝑐𝑒𝑛𝑡𝑎𝑔𝑒 𝑜𝑓 𝑎𝑠𝑕 =𝑊𝑒𝑖𝑔𝑕𝑡 𝑜𝑓 𝑎𝑠𝑕 𝑙𝑒𝑓𝑡 × 100

𝑊𝑒𝑖𝑔𝑕𝑡 𝑜𝑓 𝐶𝑜𝑎𝑙 𝑡𝑎𝑘𝑒𝑛

5. Oxygen : It is determined indirectly by deducting the combined

percentage of carbon, hydrogen, nitrogen, sulphur and ash from 100.

Percentage of oxygen = 100 – percentage of (C + H + S + N + Ash)

Q. Give the significance of the following constituents present in coal.

A. Carbon & Hydrogen B. Nitrogen C. sulphur D. Oxygen

Ans:

A. Significance of carbon & hydrogen : Greater the percentage of carbon

and hydrogen better is the coal in quality and calorific value. However,

hydrogen is mostly associated with the volatile mater and hence, it

affects the use to which the coal is put.

B. Significance of Nitrogen: Nitrogen has no calorific value and hence, its

presence in coal is undesirable. Thus, a good quality coal should have

very little Nitrogen content.

C. Significance of sulphur : Sulphur, although contributes to the heating

value of coal, yet on combustion produces acids like SO2, SO3, which

have harmful effects of coroding the equipments and also cause

atmospheric pollution. Sulphur is, usually, present to the extent of 0.5 to

0.3% and derived from ores like iron, pyrites, gypsum, etc., mines along

with the coal. Presence of sulphur is highly undesirable in coal to be

used for making coke for iron industry. Since it is transferred to the iron

44

metal and badly affects the quality and properties of steel. Moveover,

oxides of sulphur pollute the atmosphere and leads to corrosion.

D. Significance of Ash: Ash is a useless, non-combustible mater, which

reduces the calorific value of coal. Moreover, ash causes the hindrance

to the flow of air and heat, thereby lowering the temperature. Hence,

lower the ash content better the quality of coal. The presence of ash also

increases transporting, handling and storage costs. It also involves

additional cost in ash disposal. The presence of ash also causes early

wear of furnace walls, burning of apparatus and feeding mechanism.

E. Significance of Oxygen: Oxygen content decreases the calorific value

of coal. High oxygen content coals are characterized by high inherent

moisture, low calorific value, and low coking power. Moreover, oxygen

is a combined form with hydrogen in coal and thus, hydrogen available

for combustion in lesser than actual one. An increase in 1% oxygen

content decreases the calorific value by about 1.7% and hence, oxygen is

undesirable. Thus, a good quality coal should have low percentage of

oxygen.

Q. Write composition of petroleum. Describe process of Refining of

petroleum

Ans : Composition of petroleum

Carbon 80-87 %

Hydrogen 11-15 %

Sulphur 0.1-3.5 %

Oxygen 0.1-0.9 %

Nitrogen 0.4-0.9 %

Crude oil obtained from the mine is not fit to be market. It contains a lot of

soluble and insoluble impurities which must be removed.

Refining of petroleum can be defined as the process of purification and

seperation of various fractions present in petroleum by fractional distillation

45

Refining of petroleum is done in different stages

a. Removal of solid impurities: The crude oil is a mixture of solid, liquid

and gaseous substances. This is allowed to stand undisturbed for some

time, when the heavy solid particles settle down and gases evaporate.

The supernant liquid is then centrifuged where in the solids get removed.

b. Removal of water (Cottrell‘s process) : the crude oil obtained from the

earth‟s crust is in the form of stable emulsion of oil and brine. This

mixture when passed between two highly charged electrodes will

destroy the emulsion films and the colloidal water droplets coalesce into

bigger drops and get separated out from the oil.

c. Removal of harmful impurities: In order to remove sulphur

compounds in the crude oil. It is treated with copper oxide. The sulphur

compounds get converted to insoluble copper sulphide, which can be

removed by filtration. Substances like NaCl and MgCl2 it present will

corrode the refining equipment and result in scale formation. These can

be removed by technique like electrical desalting and dehydration.

d. Sweetening of Petrol: Refining of petrol or gasoline by treating it with

an alkaline solution of sodium plumbite with controlled addition of

sulphur, is called sweetening of petrol. By doing so, harmful sulphur

compounds are removed as lead sulphied.

Q. Define octane number

Ans : Defination : Octane number of a fuel is defined as the percentage by

volume of isooctane in a mixture of isooctane and n-Heptane blend, which

has the same knocking characteristic as the gasoline under test.

Knocking capacity of a fuel is measured in terms of octane number.

Branched chain compounds produce low knocking while straight chain

compounds produce high knocking. Isooctane, which has an excellent

combustion characteristics and very little tendency to knocking is given an

octane number 100. While n-Heptane this has poor combustion

characteristics and knocks badly, is given octance number zero.

46

Thus if the octane number of a gasoline is 70 it means that its knocking

characteristics are similar to that of the knocking characteristics for a

mixture of 70% isooctane and 30% n-Heptane.

Q. Define Cetane Number

Ans : Defination : Cetane number is defined as the percentage of n-Cetane in a

mixture of n-Cetane and 𝛼 − 𝑀𝑒𝑡𝑕𝑦𝑙𝑛𝑎𝑝𝑡𝑕𝑎𝑙𝑒𝑛𝑒 that has the same ignition

characteristics as the diesel fuel under test.

The Cetane number is a measure of the ease with which the given diesel fuel

will undergo compression ignition.

𝛼 -Methylnapthalene and n-Cetane are specified as standards, since n-Cetane

has low ignition lag, its cetane number is fixed as 100, while 𝛼-

Methylnapthalene has long ignition lag and its cetane number is fixed as

zero

C10H7CH3 CH3 – (CH2)14 – CH3

𝛼 − 𝑀𝑒𝑡𝑕𝑦𝑙𝑛𝑎𝑝𝑡𝑕𝑎𝑙𝑒𝑛𝑒 n-Cetane

Cetane number = 0 Cetane number = 100

Q. Distinguish between Octane number and Cetane number

Octane number Cetane number

It is the percentage of iso-octane in a

mixture of isooctane and n-heptane that

matches the fuel under test in knocking

characteristics

It is the percentage of hexadecane in a

mixture of hexadecane and 𝛼- Methyl

napthalene which have the same

knockig characteristis as the diesel fuel.

It is used to find the suitability of

gasoline or any other internal

combustion engine fuel

It is used to find the suitability of a

diesel fuel

The octane number of internal

combustion fuels can be increased by

the addition of tetraethyl lead (TEL),

(C2H5)4 Pb and diethyl telluride,

(C2H5)2Te

The cetane number of diesel fuel can be

inceased by the addition of „pe ignition

dopes‟ such as ethyl nitrite, isoamyl

nitrite, acetone.

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Q. What is natural gas? Write preperation, compostion, properties, uses

and advantages of Natural Gas

Ans : Natural gas : The natural gas is obtained from the wells dug in the earth

during mining of petroleum. It is mainly composed of methane and small

quantities of ethane along with other hydrocarbons. If the lower

hydrocarbons are present the gas is called dry gas or lean gas, but if the

hydrocarbons having the higher molecular weights are present the gas is

known as rich gas or wet gas. It is also known by the name of marsh gas as a

major portion of it is contributed by methane.

Composition of Natural gas:

Methane (CH4) – 88.5%, Ehane (C2H6) – 5.5%, Propane (C3H8) – 3.7%,

Butane (C4H10) – 1.8%., Pentane, H2, CO, CO2 and higher hydrocarbons, -

0.5%.

The calorific value of natural gas varies from 8000 – 14000 k.cal/m3.

Natural gas is subjected to various treatments before it reaches the

consumer. For example sour natural gas contains appreciable quantities of

H2S which can be removed by scrubbing with monoethanolamine.

H2S + 2HO – CH2 – CH2 – NH2 [HO-CH2-CH2-NH2]2.H2S

On heating, H2S is liberated

Uses : Natural gas is an excellent domestic fuel which can carry to long

distances in pipelines as town gas in U.S., U.K. and Mumbai highway and

also as an industrial fuel. It is also used for manufacturing a number of

chemicals like carbon black, methanol, and formaldehyde etc. methane on

microbiological fermentation give synthetic proteins which are used as

animal feed. It is also used for generation of electricity in fuel cells. Natural

gas is also used as a source of H2. Hence ammonia can be made by reacting

N2 with H2 obtained from natural gas.

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Advantages :

Is more environemnt friendly than oil or coal it is largely because of the fact

that it has only one carbon and hence, produces less emission. It is a known

fact that for the same amount of heat it emits 30% less carbon dioxide than

burning oil, and 45% less carbon dioxide than burning coal, thereby

improving the quality of air.

Q. Write preparation, advantages, disadvantages of CNG (Compressed

Natural Gas)

Ans : Natural gas contains mainly CH4

When natural gas is compressed at high pressue (1000 atm) or cooled to –

1600C it is converted into CNG. It is stored in cylinder made of steel. It is

now replacing gasoline as it releases fewer pollutants during its combustion

Advantages

Due to higher temperature of ignition, CNG is better than petrol and

diesel.

Operating cost of CNG is less

Cost of production is also less

It can be easily stored

It releases least pollutants like CO and unburnt hydrocarbons.

Spark plug of CNG engines is not carbonified.

It undergoes regular combustion

No anti-knocking agents are required as it has high octane number.

CNG run engines have long life

Disadvantages:

Response to blending is poor

Faint odour, leakages cannot be detected easily

A CNG tank requires a large tank space

Refueling network for CNG is very expensive

49

Q. Write composition, properties & applications of compressed natural gas

(C.N.G.).

Ans: Composition of C.N.G.

Methane (CH4) = 88.5%

Ethane (C2 H6) = 5.5%

Propane (C3 H8) = 3.7%

Butane (C4H10) = 1.8%

H2, Co2, H2S = Rest gases

Properties:

It is highly inflammable

It is cheaper than petrol or diesel

It has high ignition temperature (5400C)

It is odourless ,colourless & non- corrosive

It undergoes complete combustion

Its calorific value is very high

Applications/uses:

It is used as domestic & industrial fuel

It is the source of carbon black & hydrogen gas

It is used in traditional petrol I.C. engine cars

It is also used in locomotive generator to generate electricity that drives

the motor of the train

It is used as alternative fuel to petrol & diesel in metropolitan cities

Q. Describe Origin (Theory) of petroleum OR Give an account on origin of

petroleum

Ans :

Carbide theory: (Mendeleev‘s inorganic Theory) : According to this first

the carbides are formed by the reaction of metals and carbon under high

pressure and at elevated temperatures, e.g.

Ca + 3C → CaC3 calcium carbide

Mg + 3C → MgC3 magnesium carbide

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4Al + 3C → Al4C3 aluminium carbide

These carbides are then acted upon by hot water or steam to give the gases

like acetylene and methane

CaC2 + 3H2O → Ca(OH)2 + C2H2 acetylene

MgC2 + 3H2O → Mg (OH)2 + C2H2

Al4C3 + 13 H2O → 4Al (OH)3 + 3 CH4 methane

These hydro carbon gases further undergo various types of reactions like

reduction, cyclisation, polymerisation etc. to give different hydrocarbons.

𝐶2𝐻2 𝐻2 𝐶2𝐻4

𝐻2 𝐶2𝐻6

Acetylene ethene ethane

3𝐶2𝐻3 → 𝐶6𝐻6 𝑏𝑒𝑛𝑧𝑒𝑛𝑒

3𝐶2𝐻4 → 𝐶6𝐻13

Ethene hexene

3𝐶2𝐻4 → 𝐶𝐻3 − 𝐶𝐻 = 𝐶𝐻 − 𝐶𝐻3

𝑏𝑢𝑡𝑎𝑛𝑒

Toluene, methyl substituted cyclopentane and cyclohexane are formed by

different reactions.

The theory explains the formation of hydrocarbons satisfactorily but it fails

to explain

a. Presence of optically active compounds.

b. Presence of S, N, 0, compounds.

c. And presence of chlorophyll and radioactive materials. To overcome

this second theory was put forward.

Modern theory : According to this theory petroleum is formed by the

partial decomposition of marine animals and vegetable matter of prehistoric

forests. Changes in the earth (like earthquake, volcanoes) has buried these

materials underground, where they were subjected to the action of heat,

51

pressure, absence of air presence of bacteria and radioactive materials which

resulted in the decomposition of these materials into petroleum.

Q. Describe fractional distillation method of crude petroleum with the help

of labelled diagram

Ans: Fractional distillation: “The process by which petroleum is separated into

different fractions having different boiling points is called „Refining of

petroleum‟ or fractional distillation of petroleum”

Crude oil is obtained from the mines is not fit for use. It contains a lot of

impurities which must be removed. For this purpose, it is separated into a

number of useful fractions by fractional distillation.

Procedure:

1. The crude oil is heated to about 4000C in an iron retort. The hot vapours

coming out of the retort are passed through a tall vertical tower called

fractionating tower

2. The tower is fitted with a large number of horizontal trays at short

distance as shown in the fig. Each tray is provided with small chimneys

which are covered with loose caps

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3. As the vapour go up, they become gradually cooled and fractional

condensation takes place at different heights of column

4. High boiling point fractions condense first and comparatively low B.P.

fractions condense turn by turn

5. The residue left in the retort above 4000C is a black and tarry mass called

“asphalt or pitch”. It is used for making paints and as a preservative for

wood and metals. It is also used for metalling of roads

6. The different fractions of petroleum obtained after fractional distillation

are uncondensed gases, petroleum ether, gasoline (petrol), naptha,

kerosene, diesel oil, heavy oil like lubricating oil, petroleum jelly,

greases, paraffin wax, residue (asphalt)

7. All the above fractions of petroleum are collected separately and then

subjected to further purification in order to make it suitable for specific

purposes

Q. What is Petroleum oil? Illustrate various fractions obtained during

refining of crude petroleum OR Whate are the products (fractions)

obtained in refining (distillation) of petroleum oil at various

temperature range?

Ans: Petroleum oil : Petroleum or crude oil is a dark brown, viscous oil found

deep in earth crust

.

Fractions Chemical Formula Boiling range

Uncondensed gases CH4 – C4H10 Below 300C

Gasoline (petrol) C5H12 - C7 H16 30-700C

Kerosene C10 H22 - C16 H34 180-2000C

Diesel oil C12 H26 - C18 H38 250-3200C

Fuel oil C5H12 - C7 H16 320-4000C

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Lubricating oil, paraffin

wax, Asphalt

C30H62 and above Above 4000C

Q. Describe the method for determination of the gross calorific value by

using Bomb calorimeter.

Ans: Bomb calorimeter is used to find out the calorific value of solid and liquid

non-volatile fuels.

Construction of Bomb calorimeter:

A Bomb calorimeter consist of

1. Bomb pot (Cylindrical Bomb)

2. Copper calorimeter

3. Water and air jacket

4. Oxygen cylinder, battery, Pellet press

The Bomb pot is made up of stainless steel & it has a lid which is provided

with stainless steel electrodes

The Bomb is placed in a copper calorimeter which is surrounded by air

jacket & water jacket

The calorimeter is provided with an electrically operated stirrer &

Beckmann‟s thermometer

54

Working:

1. A small quantity of a fuel is weighed accurately (M Kg) and is placed in

the Bomb pot

2. Then the Bomb pot is placed in known amount water taken in a copper

calorimeter

3. Then the initial temp of water is noted as t10C with the help of

thermometer

4. After that oxygen gas is pumped under pressure 20 to 25 atm. through

the O2 valve provided

5. Then the fuel is ignited by passing electric current through the wires

provided.

6. As the fuel undergoes combustion and liberates heat, which is absorbed

by surrounding water

7. Then the water is stirred continuously to distribute the heat uniformly and

the final temp attained by water is noted t20C. The gross calorific value

of the fuel is calculated as follows:

Calculation:

Mass of the fuel = M Kg.

Initial temp of the water = t10C

Final temp of the water = t20C

Change in temp ∆ t = ( t2 – t1)0C

Specific heat of water = S

Water equivalent of calorimeter = W Kg

Gross calorific value:

GCV = W x S x t J/Kg

M

55

Chapter III

HIGH POLYMERS

Q. Define. 1) Plastic

2) Polymer

3) Polymerization

Ans:

1. Plastic: Plastic are synthetic organic materials having high molecular

weight which can be moulded into any desired shape when subjected to

heat & pressure in presence of catalyst.

2. Polymer: Polymer is a substance obtained from large number of small

molecules having low molecular weight.

3. Polymerization: It is the process of uniting (linking) together a large

numbers of small molecules (monomers) to form large molecule

(polymer) under specific conditions of temperature, pressure & catalyst

is known as polymerization.

Q. State the types of plastic. Give two example of each type.

Ans: There are two types of plastic

1) Thermosoftening plastic (Thermoplastic)

Ex: PVC,Polythene, PTFE etc

2) Thermosetting plastic Ex: Bakelite,Nylon 6:6 etc.

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Q. State the types of polymerization. Explain the types with example

Ans: Types of polymerisation

1. Addition polymerization

2. Condensation polymerisation

Ans: Additition polymerisatrion: It is the process in which monomer which

contain at least one C=C bond undergo repeated addition, resulting in the

formation of long chain polymer without elimination of simple molecules

like H2O, HCl, NH3

Example: Formation of polyethylene from ethylene

n(CH2=CH2) Polymerisation (-CH2-CH2)n

Ethylene heat,pressure, polythylene

catalyst

Condensation polymerisation

“It is the process in which the monomers of different types are joined

together by condensation forming a large polymer with the elimination of

simple molecule like H2O,HCl, and CH3OH etc.

Nylon 6:6 is obtained by condensation polymerisation of hexamethylene

diamine and adipic acid with the elimination of two water molecules.

57

Q. Thermosetting plastics are not regenerated whereas thermo softening

plastics are generated. Explain.

Ans: PVC is thermo softening plastic i.e. the plastic which can be softened on

heating & return to its original property on cooling whereas Bakelite is

thermosetting plastic i.e. the plastic which once can hardened cannot be

made soft again .

Q. Why thermosetting plastic cannot reshape and reused?

Ans: Thermosetting plastic is formed by condensation polymerization. This

plastic is hard and rigid material. It cannot be softened on heating. If it is

heated intensively, the bonds between monomers are permanently broken

and cannot reset after cooling. Therefore this plastic cannot be reshaped and

reused.

Q. Write the constituents present in plastic.

Ans: a) Resins (Binder) b) Fillers c) Pigments d) Plasticizers e) Accelerator

Q. Define Natural rubber.

Ans: Natural rubber is high molecular weight linear hydrocarbon polymer which

exhibit elasticity & other rubber like properties.

Q. Which organic compound present in the natural rubber.

Ans: Isoprene (C5H8)n is the organic compound present in the natural rubber.

Q. Define synthetic rubber .Give examples of synthetic rubber

Ans: The rubber like material prepared by chemical reaction called as synthetic

rubber.

Examples: 1) Buna-S 2) Buna-N 3) Neoprene 4)Thiokol 5)Butyl

rubber.

58

Q. What are polymers? Explain the classification of polymers with

examples

Ans : Polymers are the high molecular weight compounds obtained by repeated

union of simple molecules. (Monomers).

Ex. Starch, Polyvinyl chloride, polyethylene, Nylon 6, 6 and etc

Classification of polymers

I. Based on their sources they are classified into

1. Natural polymer: The polymers, which are obtained from natural

sources such as plants and animals, are called natural polymers.

Eg. Wood, cellulose, Jute, Cotton, Wool, Silk, Proteins, Natural rubber,

etc.

2. Synthetic Polymer : The polymers, which are synthesized from simple

molecules, are called synthetic polymers.

Eg. Nylon 66, PVC, Polystyrene, Teflon, Plexiglass, Polyesters,

Polyethylene etc.

II. Based on their thermal behaviour they are classified into

1. Thermoplastic polymer : eg : PVC, Polyethylene etc.

2. Thermosetting polymers : eg.: Bakelite, urea-formaldehyde etc.

III. Based on their mechanism of polymerization they are classified

into

1. Addition polymers : eg : PVC, Polyethylene etc.

2. Condensation polymers : eg : Nylon66, Polyester etc

IV. Based on their properties they are classified into

1. Elastomers eg : Natural rubber

2. Fibres : eg : Jute, Wood, Silk etc

3. Resins eg : urea – Formaldehyde, Epoxy resins, Phenol fomaldehyde

etc.

4. Plastics : egs: Plexiglass, PVC, Teflon etc

59

Q. What is degree of polymerization?

Ans : Degree of polymerization is a number, which indicates the number of

repetitive units (monomers) present in the polymer. By knowing the value of

DP, the molecular weight of the polymer can be calculated.

[Molecular wt of the polymer] = DP x Molecular wt of each monomer.

DP is repesented as „n‟.

Ex. (CH2 – CH2)n

Polythene

i. Calculate the molecular weight of the polythene polymer given DP is

100

Molecular weight of the polythene = DP x Molecular weight of

Polethene

= 100 x 28

= 2800

Q. Explain the free rdical mechanism addition polymerization of ethylene

Ans : The free radical mechanism polymerization of ethylene involves the

following thee steps

Initiation

Propagation

Termination

Initiation : When the initiators are heated or exposed to sunlight, they

undergo hemolytic decomposition forming highly reactive species

known as free radicals. The free radical attacks the double bond of the

monomer and initiates the chain reactions.

Examples : When dibenzoyl peroxide initiators are heated or exposed t

sunlight, they produces phenyl free radicals, which attacks the ethylene

60

monomer and converts it into reactive monomer. The reactive monomer

again reacts with another monomer and chain growth is initiated.

(C6H5COO)2 2 C6H5* + 2CO2

Dibenzyl peroxide Phenyl free radical

CH2 = CH2 + C6H5* C6H5 – CH5 – CH2*

Ethylene monomer Reactive monomer

Propagation : The active monomer again reacts with another

unsaturated monomer and converts it into monomer and growth of the

polymer chain continues

C6H5 –CH2 –CH2* + CH2=CH2

C6H5-CH2-CH2-CH2-CH2*

Reactive monomer Ethylene growing polymer chain

Termination: Termination growing polymer chain occurs by any one

of the following reaction.

Coupling of two growing polymer chain

When two growing polymer chains react with each other termination

occurs due to the formation of a dead polymer chain

C6H5-CH2-CH2-CH2-CH2* + *CH2 – CH2 – CH2 – CH2 –C6H5

Growing polymer chain Growing polymer chain

C6H5-CH2-CH2-CH2-CH2-CH2 – CH2 – CH2 – CH2 –C6H5

Dead polymer chain

b. Coupling of one growing polymer chain with free radical

When one growing polymer chains react with a free radical termination

occurs due to the formation of a dead polymer chain.

C6H5- CH2- CH2- CH2- CH2* + C6H5* C6H5- CH2- CH2- CH2- CH2- C6H5

Growing polymer chain dead polymer chain

61

Q. Explain addition polymerization with suitable example

Ans: Definition: It is the process in which monomer which contain at least one

C=C bond undergo repeated addition, resulting in the formation of long

chain polymer without elimination of simple molecules like H2O,HCl, NH3

Example: Formation of polyethylene from ethylene

In addition polymerization, monomers which are taking part in

polymerization must contain at least one double bond.

Ethylene (C2H4) is unsaturated hydrocarbon contain one C=C double

bond.

When ethylene is heated in the range 1500C to 250

0C and at the pressure

above 300 atmospheric pressure.

Then number of ethylene molecules gets united to form a long chain of

polyethylene.

During this process one of the double bonds between the carbon atoms of

ethylene (CH2=CH2) is open up and forming an unstable molecule of

ethylene. The unstable molecule (monomer) to form dimmer and the

process continues to form large molecule of polyethylene.

62

Q. Explain condensation polymerization with suitable example

Ans: Definition: “It is the process in which the monomers of different types are

joined together by condensation forming a large polymer with the

elimination of simple molecule like H2O,HCl, and CH3OH etc.

Example:“Bakelite” can be prepared by condensation of phenol with

formaldehyde in presence of acidic /alkaline catalyst.

During the reaction oxygen atom of carbonyl group of formaldehyde and

two hydrogen atoms of benzene ring of phenol are eliminated in the form of

H2O molecule.

Q. What is PTFE? Give synthesis (preparation), Properties and

Application of Teflon (PTFE – Polytetrafluroethylene)

Ans : PTFE is synthetic fluropolymer of tetrafluroethylene

Synthesis (Preparation) : Teflon is prepared by emulsion polymerization of

tetrafluroethylene (TFE). Using ammonium persulfate as initiators/ benzoyl

peroxide as catalyst under pressure

n.CF2=CF2 Persulfate intiator (-CF2-CF2)n

Tetrafluroethylene Polymerisation Teflon

Poperties

1. It has high density about 2.3 gm/cm3.

2. It has high melting point 3200C.

3. It has high degree of crystalinity.

4. It has high density.

63

5. It is insoluble is any solvent.

6. It is highly resistance to corrosive chemicals, oxidizing and reducing

agents.

7. It has high thermal stability good mechanical strength.

Applications (uses)

1. It is used for insulating material for motors, transformers, cables wires,

capacitors, generator, coils.

2. It is used for making gaskets, belt pump, valve packing, tank lining, and

chemical carrying pipes.

3. It is used as dry lubricant.

4. It is used for nonstick cooking utensils.

Q. What is PMMA? Give synthesis (preparation), Properties and

Application of Polymethyl methacrylate (PMMA) OR Plexi glass (lucite)

Ans: PMMA is transparent thermoplastic used as light weight or shatter

resistant alternative to glass.

Synthesis (Preparation) :

It is prepared by emulsion polymerization of methyl methacrylate using

hydrogen peroxide as initiator

Properties

1. It is a white transparent linear thermoplastic.

2. It has excellent optical properties.

3. It is highly resistance to heat, chemicals and water.

4. It readily allows UV – rays to pass through it

64

Applications (uses)

1. It is in air craft windows, instruments dentures (set of artificial teeth)

2. It is sued for making lenses for automobiles, artificial eyes, light fixtures

3. It is used in attractive sign boards.

4. It is used for manufacturing of transparent moulded articles and tubes.

5. It also finds uses as points and adhesives

Q. Give synthesis (preparation), Properties and Application of

Polyurethanes

Ans: Peparation : Polyurethanes are prepared by the polymerisation of

disocyanate and diol or triol.

Properties

1. They are obtained in the form of foam, fibres, elastomers etc.

2. They are less stable than polyamides at elevated temperature.

3. They are characterized by excellent resistance to abrasion and

solvents.

Application (Uses)

1. It is used as surface coating film, foams and adhesives

2. They are used for cushions in automobiles and furniture.

3. They are used to case to produce gaskets and seals.

4. These are used to coat gymnasium floor and dance floor.

5. It is used in light weight garments and swim suits.

Q. What is Bakelite? Give synthesis (preparation), Properties and

Application of Phenol formaldehyde resin (Bakelite)

Ans; It is early form of brittle (thermosetting) plastic typically brown, made

from phenol & formaldehyde.

65

Preparation: Bakelite” can be prepared by condensation of phenol with

formaldehyde in presence of acidic /alkaline catalyst.

During the reaction oxygen atom of carbonyl group of formaldehyde and

two hydrogen atoms of benzene ring of phenol are eliminated in the form of

H2O molecule.

Properties

1. They are hard, rigid and strong materials.

2. They are resistant to heat, moisture, chemicals, fires.

3. They have good abrasion resistance.

4. They have excellent electrical insulation properties.

Application

1. It is used for making electric insulator part like switches, plugs switch

boards, heater. Hands and socket for light bulb and in wire insulation .

2. It is used for making moulded articles like telephone parts, cabinets for

radio and telvision.

3. It is used as adhesive for grinding wheels and bake lining.

4. It is used in varnishes and paints.

Q. What are Elastomers?

Ans : Elastomers high polymers that undergo very long elongation (500 – 1000%)

under stress, yet regain original size fully on released of stress.

The property of elastomers is known as elasticity. This arises due to the

coiled structure of elastomers.

66

Characteristics of Elastomers

Elastomers have linear but highly coiled structure.

Inter chain cohesive forces are negligible because these are

hydrocarbons.

They have high degree of elasticity.

They can retract rapidly.

Q. Describe structure of elastomer (rubber)

Ans: Rubbers (also known as elastomers) are high polymers, which have elastic

properties in excess of 30 percent. Thus a rubber- band can be stretched to 4

to10 times its original length and as soon as the stretching force is released,

it returns to its original length. The elastic deformation in an elastomer arises

from the fact that in the unstressed condition, an elastomer molecule is not

straight chained( as in the case of plastic fibres like nylon, polyethene, etc.)

but in the form of a coil and consequently, it can be stretched like a spring

(see fig.) the unstreched rubber is amorphous. As stretching is done, the

macromolecules get partially aligned with respect to another, thereby

causing crystallization and consequent, stiffening of material (due to

increased attractive forces between these molecules). On releasing the

deforming stress, the chains get reverted back to their original coiled state

and the material again becomes amorphous.

67

Q. What are the drawbacks (deficiencies) of natural rubber? OR Why it is

necessary to vulcanize rubber? OR Vulcanization of rubber is done

before industrial use OR Natural rubber is not useful in permanent

application where elastomeric is used. Why?

Ans: The drawbacks of natural rubber are as follows:

1. During summer, the raw rubber becomes soft and sticky & in winter stiff

(hard) and brittle.

2. It has low tensile strength.

3. It is too weak to be used in heavy duty operation.

4. It has a large water absorbing capacity.

5. On stretching, it undergoes permanent deformation.

6. It is affected by the organic solvents like benzene, CCl4 etc.

Therefore, to remove the drawbacks and improve the properties, it is

necessary to vulcanize rubber.

Q. Explain Vulcanization of rubber with chemical reaction OR Describe

the process of Vulcanization of rubber .Write advantages of

vulcanization. OR Name and explain the process which increases the

stiffness of rubber OR which treatment is used to make useful the

natural rubber?

Ans: Vulcanization is the process that increases the stiffness of rubber.

Natural rubber is compounded with some substances like Sulphur, SF6, and

H2S etc.

“When natural rubber is compounded (heated) with sulphur at 100-1400

C,

the process is called as vulcanization of rubber and sulphur is called as

vulcanizing agent.”

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Process: In this process crude (raw) rubber is heated with sulphur at high

temperature. The sulphur combines chemically at the double bonds in the

rubber molecule of different rubber springs. This prevents the

intermolecular movement or sliding of rubber springs making the rubber

stiff. The stiffness depends upon amount of sulphur added.

Example:

1. A rubber tyre contains 3-5% sulphur

2. A battery case contains 30% of sulphur

3. Ebonite contain 50% of sulphur

Thus vulcanization makes the rubber tough, strong, abrasion resistance,

chemically resistant, stiff hence it is necessary to vulcanize rubber.

Advantages of vulcanization

The tensile strength increase.

Vulcanized rubber has excellent resilience.

It has broader useful temperature range (-40 to 1000C).

It has better resistance to moisture, oxidation and abrasion.

It is resistance to organic solvents like CCl4, Benzene petrol etc.

It has low elasticity.

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Q. Mention the advantages of synthetic Rubbers over natural rubber

Ans : Advantages of synthetic rubber

These are more resistance to heat and cold (nitrile rubber).

These are not easily attacked by sunlight and air (neoprene and nitrile

rubber).

These have high abrasion and high tensile strength.

Rubber property is retained at high temperatures (ex: silicon rubbers

900 - 316

0c)

Do not age easily (ex: polyurethane rubber)

Do not swell and can hold organic solvent better than natural rubber

(ex: polysulphide rubber)

Hold moist air and water at high pressure (ex: butyl rubber)

Q. Give the types of substances used in compounding of plastic

Ans: The types of substances used in compounding of plastic are fillers, resin,

plasticizers, accelerators and pigments.

Q. What is compounding of Plastic? Explain compounding of plastic. OR

What are different substances added during compounding of plastic?

Give functions of each

Ans: “The plastic are in short of some properties required for engineering

application therefore to improve the required properties some substances

like fillers, resin, plasticizers, accelerators and pigments are added into it

during polymerization. This process of addition is known as compounding

of plastic.

Fillers: These are the substances added to the plastics to improve hardness,

tensile strength, finish, workability & opacity Ex. Wood, mica, Quartz,

Asbestos

70

Resin: It is the substance which are used to bind (hold) various constituents

of plastics together also called as binder Ex. Polythene, PVC, Polyesters

Plasticizers: These are added into plastic to improve plasticity & flexibility

Ex. Camphor, Tributyl phosphate

Accelerators: It is used as catalyst which speed up polymerization process

Ex. Zncl2 , H2O2 , Calcium oxide

Pigments: Different dyes & colored pigments are added to plastic to provide

desired colour or shade. The pigment should resistant to sunlight Ex. Cobalt

blue, Chrome green, Red lead.

Q. Differentiate between Natural rubber and Synthetic rubber.

Ans:

Natural Rubber Synthetic Rubber

It is an elastic material obtained

naturally from „latex‟ of rubber plant

It is rubber like product obtained by

some chemical reaction Ex. Buna-S,

Buna-N, Thiokol,

It is an polymer of isoprene (C5H8 )n

molecule.

It is polymer of substance having

unsaturated nature

It is non resistant to oxidation It is highly resistant to oxidation

It is weak so that cannot be used in

heavy duty operation

It is strong so can be used in heavy

duty operation

It becomes soft & sticky at higher

temperature

It does not becomes soft & sticky at

higher temperature

It is plastic in nature It is elastic in nature

It is soluble in organic solvent It is insoluble in organic solvent

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Q. Differentiate between thermo softening plastic and thermosetting

Plastic. OR Write characteristics of thermosoftening and thermosetting

plastic

Ans:

Thermosoftening plastic

(Thermoplastic

Thermosetting plastic

They are prepared by addition

polymerization

They are prepared by condensation

polymerization

They have linear chain structure They have network chain structure

They have smaller molecular weight They have higher molecular weight

They can be reshaped & reused They cannot be reshaped & reused

They are soft, weak & less brittle They are hard, strong & more brittle

They are soluble in organic solvent They are insoluble in organic solvent

They can be reclaimed from waste They cannot be reclaimed from waste

They are linked by weak covalent bond They are linked by strong covalent

bond

Ex: Polyethylene,PVC Ex: Bakelite,Polyster.

Q. State properties of plastics.

Ans: Properties of plastic

1. They are light in weight and have specific gravity from 1 to 2.4

2. They have low thermal and electrical conductivity.

3. They are highly resistant to corrosion and machined.

4. They can readily mould, drilled and machined.

5. They have low melting point.

6. They are not attacked by fungi, insects etc.

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7. They have low coefficient of thermal expansion.

8. They have good tensile strength (5500 kg/cm2).

9. Plastics are good mechanical shock absorbers.

10. Their shades or colours do not fade easily.

11. They are highly resistant to the attack of light, oil, acids and moisture.

Q. Differentiate between addition polymerization and condensation

polymerization

Ans:

Addition polymerization

Condensation polymerization

It is the process in which monomers

undergo repeated addition resulting in

the formation long chain polymer

without elimination of simple

molecules like H2O, HCl, and NH3

It is the process in which monomers

of different types are joined together

by condensation forming a large

polymer with the elimination of

simple molecule like H2O, HCl,

CH3OH

Unsaturated monomers undergo this

reaction

Functional monomers undergo this

reaction

For this low pressure &temperature is

required

For this high pressure &

temperature is required

Thermo softening plastic are prepared

by this method

Thermosetting plastic are prepared

by this method

Linear or chain structure is formed in

Polymer

Three dimensional structure is

formed in polymer

It is fast reaction It is slow reaction

Reaction gives only main product Reaction gives main product &

subsidary product

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Q. Write applications of plastic based on its properties.

Ans: Applications of plastic

Due to “low density and high tensile strength” plastic are used in aircraft,

motor cars and in structural industries.

Due to low “electrical conductivity they are used in electronic industry

for electrical insulation of PCB, cabinets of TV, computer.

Due to “low thermal conductivity” they are used for making handles of

electric irons, soldering gun, pressure cookers etc.

It is used as thermal insulator in refrigerator, air conditioners, cold

storage etc.

Due to “corrosion resistant and chemical resistance” they are used in

chemical industry in manufacturing of tanks, tubes, pipes, absorption

towers etc.

Due to their “high shock absorbing capacity” they are used for making

parts of machinery to reduce noise and vibration.

Due to “optical clarity” they are used for making glass fiber and wind

screens for automobile and aircraft.

As plastic is „water resistant‟ used in manufacturing of polythene bags,

containers, bottles, pipes floor covering, rain coats etc.

As „light in weight‟ and “strong” it is used in furniture like chairs , tables,

stools, decorative items like clocks, toys, panels sheet, mirror case etc.

Q. Explain the structure of thermosoftening and thermosetting plastic

Ans: Structure of thermosoftening plastic: This plastic is formed by addition

polymerization. It has long chain linear polymer with negligible cross links. Its

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monomer has atleast two active valencies. Under suitable conditions these

valencies links with other similar monomers forming linear chain as shown below

If M is monomer

Structure of thermosetting plastic: This plastic is formed by condensation

polymerization. It has three dimensional network chain structure. Its

monomer has at least three active valencies. Under suitable condition these

valencies link with other type of monomers forming network chain structure

as shown below

If M is monomer

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Q. Explain the following properties of synthetic rubbers.

1. Elasticity 2. Tack 3. Abrasion resistant

4. Tensile strength 5.Hardness 6.Rebound

Ans: Properties of synthetic rubber

1. Elasticity: Elasticity is the property by virtue of which a material undergoes

deformation under stress and regains its original shape on removal of the

stress. Ex: rubber bands, automobile tubes.

2. Tack: Tack is the special characteristic of rubber by virtue of which two or

more surface can stick to each other.Ex: In manufacturing of rubber tyres.

3. Abrasion resistance: Abrasion resistance is process of wearing away the

surface of rubber by friction.Ex: Automobile tyres, shoe soles.

4. Tensile strength (stress and strain): When a dumbbell shaped piece of

rubber is taken and placed in the machine and further it is stretched until it

breaks. The load at which it breaks is its tensile strength

Ex. V belts and conveyor belts.

5. Hardness: Hardness is ability of rubber to with stand wear, abrasion and

resists penetration. Ex: shock absorber, gaskets etc

6. Rebound: It is the ability to absorb energy and return without permanent

deformation of a synthetic rubber.Ex: Rubber ball will bounce when

dropped used in shock absorbers.

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Q. Write any four applications of rubber (elastomers) with their related

engineering properties. OR Give applications of synthetic (vulcanized)

rubber.

Ans: Applications of rubber(elastomer)

Properties Based application

Elasticity, toughness, tensile strength

For making rubber bands, tubes of

vehicles, sports goods, telephone

reciever, ball etc.

Abrasion resistant

Used in tyres of vehicles, shoe heels

and Soles, V-belt, conveyor belt, floor

tiles, Rubber mats, etc.

Bad conductor of electricity

Used for insulation wires and cables,

switch board panels, plug, sockets, and

battery cases.

Hardness

Rubber gaskets are used for sealing

refrigerator, cabinet doors, cookers,

autoclave etc.

Chemical resistance

Rubber is used for lining in chemical

tank, as gaskets, rubber seals, pumps

etc.

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Q. Write preparation, properties and application of Buna-S or Styrene

Rubber

Ans : Buna – S ruber is probably the most important type of synthetic rubber,

which is produced by copolymerization of butadiene (about 75% by weight)

and styrene (25% by weight)

nCH2=CH-CH=CH2 + nCH2=CH-Ph -(-H2C-CH=CH-CH—CH2-CH-Ph-)n-

1,3-butadiene (75%) Styrene (25%)

Properties: Styrene rubber resembles natural rubber in processing

characteristics as well as quality of finished products

It possesses high abrasion resistance, high load bearing capacity and

resilience.

It gets readily oxidized, especially in presence of traces of ozone

presents in the atmosphere.

It swells in oils and solvents.

It can be vulcanized in the same way as natural rubber either by sulphur

or sulphur monochloride.

It requires less sulphur, but more accelerators for vulcanization

Applications (Uses)

1. It is mainly used for the manufacture of motor tyres.

2. It is used for floor tiles, shoe soles, gaskets, foot-wear components,

wire-cable insulations, carpet backing, adhesives, tank-linings

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Q. Write prepation, Properties and applications of Butyl Rubber (G-I or

Polyisobutylene)

Ans :

Preparation :Butyl rubber is prepared by the aluminium chloride initiated

cationic co-polymerization of isobutene with small amount (0.5 to 2.5%) of

isoprene.

Properties : Butyl rubber has following characteristics

Under nomal conditions it is amorphous but it crystallizes on stretching.

It is quite resistant to oxidation due to low degree of unsaturation.

Due to very low unsaturation, it can be vulcanized but it cannot be

hardened much.

It can be degraded by heat or light to sticky low molecular weight

products so stabilization is must.

Butyl rubber is soluble in benzene but has excellent resistance to polar

solvents like alcohol, acetone.

Compared to natural rubber it possesses outstanding low permeability to

ai and other gases.

Application : Butyl rubber used for

Insulation of high voltage wires and cables

Inner tubes of automobiles tyres.

Conveyor belts for food and other materials.

Lining of tanks and Hoses.

79

Chapter IV

CORROSION SCIENCE

Q. Define corrosion.

Ans: “Any process of chemical or electrochemical decay (destruction) of a metal

due to the action of its surrounding medium is called as corrosion”.

Example: Rusting of Iron

Q. State the types of corrosion.

Ans: There are two main types of corrosion namely,

1. Atmospheric corrosion or Dry corrosion/Direct chemical corrosion

2. Electro chemical/Wet/Immersed corrosion

Q. Define Atmospheric corrosion/Dry corrosion. Give two examples

Ans: The corrosion which is brought out by atmospheric condition is called as

atmospheric corrosion or

The corrosion which is caused by direct chemical action of gases like O2,

halogens, SO2, H2S with metal surface is called as atmospheric

corrosion/dry corrosion

Example: 1. Rusting of Iron.

2 Formation of green film of basic carbonate on the surface of copper

Q. State the factors affecting rate of atmospheric corrosion.

Ans: Factors affecting atmospheric corrosion are

1. The impurities present in the atmosphere.

2 . Moisture in the atmosphere

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Q. Define Electrochemical/Wet corrosion/Immersed corrosion

Ans: “The corrosion of metal which take place in presence of liquid (Solution)

through ionic reaction when two dissimilar (different) metals are in contact

with each other is called as electrochemical/wet/immersed corrosion.”

Q. Give two examples of electrochemical corrosion.

Ans: a) Steel pipe connected to copper plumbing

. b) Copper sheets joined by iron nails.

c) Corrosion at rivetted joints

Q. State the factors affecting rate of electrochemical/immersed /wet

corrosion.

Ans: 1. PH value of solution

2. Purity of metal

3. Position of metal in electrochemical series

4. Solubility of the corrosion product

5. Area of cathode and anode

6. Nature of metal surface

Q. State the necessary condition for electrochemical corrosion to take

place.

Ans: a) Formation of anodic and cathodic area

b) Presence of conducting medium which acts as electrolyte

c) Electrical contact between anode and cathode for conduction of electron

Q. Why protection from corrosion is necessary? OR Give disadvantages of

corrosion

Ans: Corrosion causes many effects as

1. It reduces the life span of machine

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2. It weakens the metallic structure and machinery which may causes

injuries to worker

3. It causes loss of cost of extraction of metal from their ores, cost of

fabrication of metal etc. Due to above reasons protection from corrosion

is necessary.

Q. Name different methods of applying metal (protective) coating OR List

different methods used for the prevention of corrosion.

Ans: Methods used for protective coating

1. Hot dipping : a) Galvanising b) Tinning

2. Metal spraying

3. Electroplating

4. Metal cladding

5. Cementation : a) Colorizing b) Chromizing c) Sheradizing

Q. What is cathodic protection? Give one example.

Ans: Cathodic protection is a method in which the base metal to be protected from

corrosion is made to acts as cathodic by attaching more active anodic metal

to it. e.g.: Protection of underground pipelines

Q. Why Galvanized containers are not useful for storing food and food

stuff (material).

Ans: Galvanized containers are not useful for storing or preparation of food stuff

because galvanized containers have a coating of zinc. This zinc metal reacts

with the acids present in food stuff and forms highly poisonous compounds

which are harmful for human consumption.

82

Q. Which property of tin makes useful for tinning? Why?

OR Tinned articles are used for storing food stuff. Why? OR Tin coated

utensils are mostly preferred to zinc coated utensils for the storage of

food stuff. Explain

Ans: In tinning base metal iron is coated with thin layer of tin (Sn). Tin (Sn) is

less electropositive than iron, hence it is more resistant to chemical attack

and thus protects the base metal. Due to its non-toxic nature and resistance

to chemical attack tinned articles are used for storing food stuff.

Q. Explain mechanism of Dry/ atmospheric/chemical (oxidation) corrosion

OR

Explain mechanism of corrosion due to action of oxygen

Ans: “Oxidation corrosion” is brought about by direct chemical action of oxygen

on metals or by forming “oxide film”.

2M + O 2 2MO

Metal Metal oxide

1. When metallic surface comes in contact with atmospheric oxygen then

metallic ion is formed.

2. Then the electrons from metal are transferred to oxygen and oxide ion is

formed.

3. Then the metallic ion and oxide ion combine together to form metal

oxide.

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4. The mechanism of oxide film formation can be represented by the

following equation,

M M++

+ 2e – (oxidation – loss of e

-)

+ O + 2e-

O - - (Reduction – gain of e-)

M + O M++

+ O- -

MO (Metal oxide)

Metal Oxygen Metallic Oxide

ion ion

Q. Explain the factors which affect the rate of atmospheric corrosion.

Ans: The factors which affect the rate of atmospheric corrosion are

1. Impurities in the atmosphere

2. Moisture in the atmosphere

1. Impurities in the atmosphere :

In industrial area the air contains the corrosive gases like CO2, H2S, SO2

along with acidic impurities such as H2SO4, HNO3 and HCl etc. In all of

these SO2 is most corrosive factor. In the presence of such acidic

impurities the corrosion of metals becomes faster.

2. Moisture in the atmosphere:

The rate of corrosion increases in the presence of moisture. The

atmospheric gases or chemical vapours are dissolved in the moisture. The

reaction between such dissolved gases with metallic surface becomes

faster. Therefore moisture acts as conducting medium and increases the

corrosion.

Ex. Rusting of iron increases in presence of moisture.

84

Q. Explain mechanism of electrochemical/chemical/wet/immersed

corrosion by using Daniel cell (Galvanic cell action).

Ans: The mechanism of electrochemical corrosion can be explained by using

Daniel cell

Construction:

Daniel cell consist of Zn and Cu electrodes which are dipped in ZnSO4 and

CuSO4 solution respectively. These two solutions are separated by a porous

partition to prevent mixing of two solutions. Zinc and copper electrodes are

connected by a metallic conductor.

Working: The EMF is developed due to two separate reactions taking place

at the two electrodes.

a. Zinc metals is higher in the electrochemical series acts as anode

and goes into the solution as Zn++

ions with liberation of electrons

At anode:

Zn(s) Zn++

(aq) + 2e- (oxidation)

85

b. The liberated electrons move along metallic conductor and are accepted

by copper which acts cathode.

At cathode:

Cu++

(aq)+ 2e- Cu(s) (reduction)

Thus, zinc goes into the solution (get dissolved) and corroded, while copper

is deposited at cathode and get protected.

Q. Explain the factors which affect the rate of

electrochemical/wet/immersed corrosion.( Any four ) OR How nature of

metal and environment responsible for corrosion?

Ans: Following are the main factors which affect the rate of electrochemical

corrosion.

A . Nature of metal

1. Position of metal in electrochemical series: In electrochemical series,

elements are arranged in the order of their decreasing activity. Therefore

top elements are more active than that of bottom element. So top

elements are easily oxidized and get corroded easily.

2. Purity of metal: The impurity present in metals form minute

electrochemical cell and the anodic part get corroded. Hence, rate of

corrosion also increases with increase in impurities present in the metal

3. Area of anode and cathode: If the cathode area is large in comparison

of anode then corrosion increases and vice-versa because there is more

demand for electrons by larger catholic area

4. Nature of oxide film: If the oxide film is non porous then the metal

protects itself from corrosion. But if the oxide film is porous then the

corrosion by the gas continues

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B. Nature of environment

1. PH value of the solution:

PH value of solution indicates the acidity or alkalinity of solution. Acidic

solutions are more corrosive to metals than neutral or alkaline solution;

hence solution with PH value less than 7 causes more corrosion.

2. Temperature: An increase in temperature results in an increase in

conductance of aqueous medium and rate of corrosion increases and

vice-versa

3. Humidity: Humidity air is directly related to the rate of corrosion. In

humid condition atmospheric gases easily form electrochemical cell by

which corrosion occurs to great extent

Q. Describe mechanism of electrochemical corrosion with evolution of

Hydrogen gas

Ans: The hydrogen evolution mechanism of electrochemical corrosion takes place

in acidic environment like industrial waste.

Mechanism: Consider a steel (Fe) tank which contains acidic solution

(waste) and a small piece of copper. As copper and iron come in contact

87

and surrounded by acidic solution, then galvanic cell is formed. Then large

steel tank (Fe) becomes anode and small copper becomes cathode.

Working:

1. At anode: Electrons flow through the metal from anode to cathode

Fe Fe++

+ 2e- (oxidation)

2. At cathode: At cathode, H+ ion present in acidic solution are eliminated

as hydrogen gas

2H+

+ 2e- H2 (reduction)

Net reaction: Fe + 2H+

Fe++

+ H2

Thus, iron (steel) gets corroded in acidic reaction.

Q. Describe mechanism of electrochemical corrosion with absorption of

oxygen gas

Ans: This type of corrosion takes place in neutral or alkaline medium

Example: Consider “Rusting of iron” take place in presence of neutral or

alkaline medium.

88

Mechanism:

Consider a steel (Fe) surface exposed to atmosphere, after a course of time

iron oxide layer is formed on the surface of steel (Fe) plate. If there is a

small crack developed in iron oxide layer and a drop of water (moisture) is

collected in crack, then

a. Water acts as electrolyte

b. Small crack acts as anode

c. Iron oxide covered steel surface acts as cathode.

Working:

At anode: The liberated electrons flow through anodic area to cathodic area.

2Fe 2Fe ++

+ 4e- (oxidation)

At cathode: The dissolved oxygen present in moisture (water) .The

electrons are reacting with water and dissolved O2

2H2 O + O2 + 4e- 4OH

- (reduction)

The net reaction:

2Fe + 2H2O + O2 2Fe++

+ 4OH- 2Fe (OH) 2 brown rust

If enough O2 is present Fe (OH) 2 oxidised to Fe (OH)3 which is called as

yellow rust

4Fe (OH)2 + 2H2O + O2 4Fe (OH) 3 yellow rust

89

Q. What is sacrificial anodic (Galvanic) protection? Explain sacrificial

anodic protection method of prevention of corrosion. OR How

sacrificial anodic protection can be done?

Ans: Sacrificial anodic protection: In this method the metallic structure to be

protected from corrosion is connected to the anodic metal (active) by an

insulating wire is known as sacrificial anodic protection.

Method: The more active metal like Zn, Mg, and Al (acts as anode) are

connected to the metal structure to be protected so that the chemical

reactions are taking place at the more reactive metal surface and thus saving

the metal structure from corrosion as shown in fig. and gets corroded, hence

it is known as sacrificial anode.

For the purpose of increasing electrical contact, the active metal is placed in

back fill (Coal + NaCl). The sacrificial anode has to be replaced time to time

after complete corrosion..

Example: Several hundred kilometers long zinc wire is buried along oil pipe

line in Alaska

Applications:

1. It is used for protection of ships and boats

2. It is used for protection of underground pipeline, cables from soil

corrosion

90

Q. Explain impressed current cathodic protection method of prevention of

corrosion. Write its applications.

Ans: In this method the corroding metal is converted from anode to cathode by

applying impressed current to the metal to be protected and is itself used as

cathode.. This can be done by applying amount of direct current from D-C

source to an anode

Method: In this method

1. The negative terminal of battery is connected to the metal

2. The positive terminal of battery is connected to an inert anode

3. The inert anode used is graphite platinized titanium

4. Then the anode is buried in a “back fill” to provide electrical contact.

5. Then oxidation reaction is taking place at the cathode electrode and

electrons are liberated, which are repelled by the cathode electrode.

6. As result, the anode electrode destruct and has to replaced time to time

7. Thus cathode electrode protected from corrosion

Applications: This method is applicable to protection of Open water box

coolers, Water tank, Buried water or gas pipeline, Condensers, Transmission

line tower, Ships

91

Q. Explain Galvanising method. OR Describe the process of protecting

steel articles from corrosion by coating of zinc over it. OR How

galvanizing is done?

Ans: Galvanising:“The process of coating of zinc on the surface of iron (steel)

by hot dipping method to prevent it from corrosion is called as galvanising”

The method involves following steps:

1. The iron (steel) sheet to be galvanised is first cleaned by dil. H2SO4 to

remove rust, dirt and oxide layer on the surface of iron

2. Then it is washed with water to remove acid completely and dried

3. Then the sheet is dipped in bath of molten zinc at 425oC to 460

oC

temperature. Then it is passed through ammonium chloride and zinc

chloride flux to prevent oxidation of zinc

4. Then the metal sheet is passed through a series of rollers & to get

uniform coating.

5. Finally galvanized sheet is annealed at a temperature 6500C

Applications:

This method is used for roofing sheets, water pipes, bars, rods, fencing wires

etc.

92

Q. Explain Tinning method. OR Describe the process of protecting steel

articles from corrosion by coating of tin over it. OR How tinning is

done?

Ans: Tinning: “It is the process of coating of tin metal on the surface of iron

(steel) by hot dipping method to prevent it from corrosion is called as

tinning.”

The method involves following steps:

1. The iron (steel) sheet to be tinned is first cleaned by dil. H2SO4 to

remove rust, dirt and oxide layer on the surface of iron

2. Then it is washed with water to remove acid completely and dried

3. Then the sheet dipped in bath containing ammonium chloride and zinc

chloride flux and then it is dipped in molten tin

4. Finally it is dipped in palm oil to prevent oxidation of tin

5. Then the metal sheet is passed through a series of rollers to remove

excess of tin & to get uniform coating

Applications: Tinning is used for coating steel used for manufacturing of

containers for storing food stuff, oil, ghee, pickles etc.

93

Q. Distinguish between galvanizing and tinning.

Galvanizing Tinning

1. The process of coating a base

metal like iron or steel with

zinc by hot dipping method is

called as galvanizing.

2. If a scratch or gap is produced

on a galvanized surface, zinc

will corrode and iron will be

protected.

3. In the above case, corrosion of

zinc will not take place very

fast because anodic area (Zn) is

large.

4. Galvanized articles cannot be

used for storing food stuff but

galvanized sheets are mostly

used for manufacture of roofing

sheets, buckets etc.

5. Zinc protects the iron from

corrosion because zinc is more

electropositive than iron.

1. The process of coating a base

metal like iron, steel or copper

with tin by hot dipping method

is called as tinning.

2. If a scratch or gap is produced

on a tinned surface, tin will not

be corroded, instead iron starts

corroding.

3. In the above case, corrosion of

anode (iron) takes place very

fast because anodic area is

small.

4. Tinned articles are mostly used

for storing and preparing food

Stuff.

5. Tin protects the iron from

corrosion because tin is less

electropositive than iron.

94

Q. Explain Differential metal corrosion?

Ans: Differential metal corrosion:

This type corrosion occurs when two different metals are in contact with

each other due to the formation of galvanic cell. The metal having less

standard reduction potential value under goes oxidation and liberates

electrons, which migrates to the cathode. The other metal having high

standard reduction potential (SRP) value acts as cathode and reduction

reaction takes places on its surface forming OH- ions or any one kind of

reduction reactions. The rate of corrosion depends on the potential difference

between the two metals. If the difference is more corrosion occurs faster and

vice versa. The anodic metal undergoes corrosion and cathodic metal is

unaffected. The reactions that occurs are

At anode M → Mn+

+ ne-

At cathode depending on the nature of corrosion environment the cathodic

reaction are as follows

2H+ + 2e

- → H2 (in acidic environment)

H2O + O2 + 4e- → OH

- (in neutral environment)

2H2O + 2e- → 2OH

- + H2 (in alkaline environemnt)

Example : Iron metal in contact with Copper metal, Brass tap in contact

with Iron pipe etc.

95

Q. What is differential aeration corrosion? Explain waterline corrosion

and pitting corrosion

Ans : Differential aeration corrosion: This type of corrosion occurs when

a metal is exposed to different concentrations of oxygen. The part of metal

which is more exposed to air acts as cathode and unaffected. The other part

of the metal, which is less exposed to air act as anode and undergoes

corrosion

Water line corrosion:

It is differential aeration type of corrosion .Corrosion observed in water

tanks, storage tanks and marine structures are called as water line corrosion.

When water is stored in an iron tank, it is found that maximum corrosion

occurs along a line just below the water level. The area above the H2O line

is highly oxygenated and acts as cathode while the area just below the H2O

line is less oxygenated and acts as anode and undergoes corrosion.

At anode Fe Fe++

+ 2e -

At cathode 2Fe++

+ 4OH - 2Fe (OH) 2

2Fe (OH)2 + O2 + 2H2O 2(Fe2O3. 3H2O) rust.

96

Pitting corrosion: Pitting corrosion occurs when small particle like dust,

mud etc get deposited on metal surface.

This gives rise to the formation of small anodic and cathodic areas. The

portion of metal covered by the dust or other particles is less aerated and act

as anode. The other portion of the metal exposed to more oxygen of the

environment acts as cathodic region. Corrosion takes place at the portion

below dust and a small pit is formed. Then the rate of corrosion increases

due to small area and large cathodic area.

Q. Explain the Anodic Protection method. OR How metal protected by

anodizing?

Ans: Anodic protection method

97

Method: In this method, the metal to be protected from corrosion is made

more anodic by passing external impressed current to make it more anodic

and it forms a thin oxide film which then protects the metal from further

corrosion. The metal part is connected to potentiostat for maintaining

constant potential having a reference electrode the auxiliary electrode acts as

cathode and base metal acts an anode after passing current the metal from a

passive layer which prevents further corrosion.

The advantage of the method is that it requires small current.

A drawback of this method is that is cannot be applied to the metals which

do not passivate.

Q. Explain the process of Phosphating (Phosphate coating). OR How metal

protected by phosphating?

Ans: Phosphate coating is a process of converting the surface atoms of the base

metal into their phosphates by chemical or electrochemical reaction between

base metal and certain metal phosphates in aqueous solution of phosphoric

acid.

Phosphate coating is generally obtaining on steel. Al, and Zn.

It involves following steps

The metal to be coated (base metal) is degreased, polished washed and

dried

It is dipped in a solution containing mixture of phosphoric acid, metal

phosphates such as Fe/Mn/Zn phosphates.

98

Accelerators such as copper salts. H2O2, nitrate etc.

pH of the bath is maintained about 350 C.

The metal ions dissolve and react with phosphate ions forming metal

phosphate.

The metal phosphates deposits on the surface of base metal.

Uses:- Phosphate coated metal widely used in automobile industry, bolts,

nuts, and refrigerators, washing machining, cars bodies etc.

99

LUBRICANTS

Q. Define lubricant. State the types of lubricant.

Ans: - Definition: The substance which is used to reduce the frictional resistance

between two moving (sliding) surfaces is known as lubricant.

There are mainly three types of lubricant namely,

1. Solid lubricant – graphite, soap

2. Liquid lubricant- palm oil, whale oil

3. Semisolid lubricant – grease, waxes

Q. Define lubrication. State the types of lubrication

Ans: Definition: The process of reducing the frictional resistance (force)

between two moving (sliding) surfaces by the introduction of lubricants

between them is known as lubrication.

There are three types of lubrication namely,

a. Fluid (thick) film lubrication

b. Thin (boundary) film lubrication

c. Extreme pressure lubrication

Q. Define viscosity & viscosity index. Give their significance.

Ans: Viscosity: It is defined as the force in dynes required to move 1cm square

of liquid over another surface with velocity of 1 cm/sec. It is expressed in

poise.

Significance of viscosity: It determines the main oprating characteristics of

the lubricant

Depending on the load conditions in lubrication oil of different viscosities

are selected. For e.g. for low load condition, an oil of lower viscosity is

required while for high load conditions, oil should have higher viscosity.

Viscosity index

Definition: “The rate of change of viscosity of lubricating oil with

temperature is called viscosity index”

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Significance:

A good lubricant should have minimum variation of viscosity with

temperature i.e. viscosity index.

For e.g. Butter has low viscosity index hence it cannot be used in

machines where temperature change is rapid.

Q. Define oiliness. Give its significance

Ans: “It is defined as the power of an lubricant (oil) to maintain a continuous

film under pressure”.

Significance:

1. Oiliness is important in extreme pressure lubrication

2. Oil with poor oiliness have tendency to be squeezed out of the machine

parts under high pressure

3. A good lubricant should have sufficient oiliness under working condition

Q. Define flash point & fire point. Give their significance

Ans: Flash point: Flash point is the lowest temperature at which the oil lubricant

gives of enough vapours that gives momentary flash of ligh when a small

flame is applied to it.

Fire point: Fire point is the lowest temperature at which the oil lubricant

gives of enough vapours which catches the fire & burn continuously at

least for 5 second when a small flame is applied to it.

Significance:

A good lubricant should have high flash point and fire point.

The knowledge of flash point of lubricant aids in precautionary measures

against fire hazards.

Oil of high flash point is supposed to offer more resistance to spontaneous

combustion

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Q. Define cloud point & pour point. Give their significance.

Ans: Cloud point: When oil is cooled slowly, the temperature at which it

becomes cloudy or hazy in appearance is called as its cloud point.

Significance:

1. A good lubricating oil should have low cloud point 1.

2. The cloud point indicates the suitability of lubricant in cold condition

Pour point: When oil is cooled slowly, the oil ceases (stops) to flow is called

as its pour point.

Significance:

1. Pour point determines suitability of lubricant for low temperature

condition

2. Lubricant used in the machine working at low temperature should posses

low pour point

3. It indicates the dissolved wax concentration in given sample of oil & also

determine the temperature below which oil cannot be used as lubricant in

the engine

Q. Define

1. Acid value [Neutralization number]

2. Saponification value

3. Emulsification.

4. Aniline point

1. Acid value [Neutralization number]

It is defined as number of milligrams of KOH required to neutralize free

acid in 1gm of oil.

Significance

a. A good lubricant should have low acid value less than 0.1 because free

acid present in lubricant causes corrosion of machine parts and value

greater than 0.1 shows that oil has been oxidised

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b. A lubrication oil should posses acid value less than oil

Determination of Acid Value:

Procedure:

1. Take 10-20 gms of oil in a conical flask and add 50 cc of water, 50 cc

alcohol and few drops of phenolphthalein indicator

2. Titrate the solution with N/10 KOH solution til pink colour is obtained

at the end point

Neutralization number = (No. of cc of N/10 KOH ×5.6)

(weight of oil taken)

2. Saponification value

It is defined as number of milligrams of KOH required to saponify 1gm of

lubricating oil.

Significance

With the help of saponification value we can know whether the oil is

vegetable, animal or mineral

A good lubricating oil should have moderate (high) saponification value.

3. Emulsification

It is defined as “the tendency of lubricating oil to mix with water to form

a stable emulsion i.e. homogeneous mixture of oil & water”.

Significance

The emulsion have tendency to catch the dust and other particles from its

surrounding which causes failure of lubrication system. Therefore a

good lubricant should have low emulsification number.

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4. Aniline point: Aniline point of oil is defined as the minimum

equilibrium solution temperature for equal volumes of aniline and oil

sample.

Significance: Aniline point gives an indication of the possible

deterioration of oil in contact with rubber, sealing packing etc.

A high aniline point of lubricant indicates that it contains higher % of

paraffinic hydrocarbons and lower % of aromatic hydrocarbons

Determination of aniline point:

Aniline point is determined by mixing; mechanically equal volumes

of the oil sample and aniline in a test tube.

The mixture is heated, till homogenous solution obtained.

Then the test tube is allowed to cool at a control rate.

The temperature at which the two phases (oil and aniline) separate out

is recorded as the aniline point.

Q. Lubricant is added along with fuel in IC engine. Justify.

Ans: Lubricant is added with fuel in IC engine because it reduces the power loss

in internal combustion engine. Because in internal combustion engine, the

lubricant acts as a seal between the piston & cylinder wall hence it prevents

the leakage of gases at high temperature.

Q. Wites the characteristics (properties) &uses of graphite.

Ans: Characteristics (Properties)

1. It is stable at high temperature

2. It is non-inflammable

3. It is very soft

4. It is not oxidized in air below 3750 c

5. It is used up to very high temperature in the absence of air

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Uses: It is used as lubricant in air compressors, lathes, food stuff industry,

railway track-joints, open gears, chains, cast iron, bearings, I.C. engine tube

drawing, forging etc.

Q. Write the characteristic & uses of molybdenum disulphide (MoS2)

Ans: Characteristics:

1. It is used in fine powder form

2. It is stable at high temperature & pressure

3. It adheres well to the metal surfaces

4. It has low coefficient of friction

Uses:

1. It is used for lubricating machine which are subjected to high temperature

2. It is also used as grease additive under required conditions which is used

in automotive & truck chasis

3. It can be used in vacuum & therefore can be used in space craft

Q. Write the characteristics & uses of grease (plastic lubricant)

Ans: “Greases are the mixture of petroleum oil & soaps”.

Characteristics:

1. Its structure is like a gel

2. They have higher frictional resistance than oil

3. It supports much heavier load at lower speeds

4. They are more convenient in use

Uses: They are widely used as

1. Where gears & bearing works at high temperature

2. Where bearing needs to be sealed against entry of dust, dirt, moisture

3. Where oil cannot remain in place of machine parts

Ex- Rail axle boxes

4. Where oil gives splashes (dripping)

Ex- textile, edible articles, machines, preparing paper

105

Q. Writes the characteristics & uses of silicone oil (fluid)

Ans: Characteristics:

1. They have high viscosity index

2. They have good oxidation resistance

3. They are chemically inert

4. They are non-inflammable

5. They have high flash point

6. They are water & corrosion resistant

Uses:

1. They are useful for rubber & plastic surfaces including moving picture

film, slide roles, gears bushing, bearing

2. It is used as moisture repellent

3. It is used as dielectric lubricant for clocks time & other electronic devices

Q. What are the functions of Lubricants?

OR

Write any four functions of Lubricants.

Ans : The functions of lubricants are as follows

1. It reduces wear & tear & surface deformation by avoiding direct contact

between the rubbing surface

2. It reduces the loss of energy in the form of heat by acting as a coolant.

3. It reduces the expansion of metal by local frictional heat

4. It reduces the maintaince & running cost of machine

5. It increases the efficiency of the machine by reducing the waste of energy

6. It reduces the power loss in internal combustion engine

Q. State the types of lubricants with example. OR Classify lubricants with

example

Ans: There are mainly three types of lubricants namely,

1. Solid Lubricant

2. Liquid Lubricant

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3. Semi – Solid Lubricant

1) Solid lubricant

Ex. Graphite, molybdenum disulphide, soap, wax, talc, mica, chalks etc

2) Liquid lubricant

Ex. a) Vegetable oils – Palm oil, Castor oil

b) Animal oils – Whale oil, Tallow oil,

c) Mineral oil- Paraffin, Naphthalene

d) Blended oil – Mineral oil + animal oil, Mineral oil + vegetable oil

e) Synthetic oil – Polymerized hydrocarbon, polyglycols, organic amines

3) Semi Solid lubricants

Ex.Greases and Vaseline

Q. How lubricants are selected?

Ans: The selection of lubricant is depends upon on following points,

1. It requires the study of working condition such as speed, pressure

temperature and heat produced.

2. A selected lubricant should neither be very thick nor be very thin.

3. A selected lubricant should form a continuous film between the moving

parts of machine

4. A selected lubricant should not adhere to moving parts & thus prevents

the movement of it

The selection of lubricant depends on operating condition

Operating condition Types of lubricant

1. High speed and heavy load Extreme pressure lubricant

2. Low speed heavy load High oiliness boundry film

lubricant

3. Less load and high speed Oil with low viscosity

4. Low temperature High fluidity

5. High temperature Oxidation resistance and less

viscosity

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Q. With reason, suggest proper lubricants for sewing machine rollers,

delicate instruments gears, cutting tool, and internal combustion engine,

transformer

Ans: For Sewing machine: It is delicate instrument which is not exposed to high

temperature, heavy loads or to water so that mineral oil, silicones, thin

vegetables and palm oil like palm oil, neat foot oil are used as lubricant

Road rollers: It is machinery in which extreme pressure and low speeds are

employed where thick oil film cannot be maintained so that solid lubricants

like graphite, Soap-stone, mica, molybdenum disulphide are most commonly

used

For Delicate instrument (equipments):

Delicate instruments like watches, clocks, scientific instruments, sewing

machine are not exposed to high temperature, pressure load and heavy load

or there is heavy friction between the rubbing parts. Therefore lubrication oil

like thin vegetable oil, palm oil neat foot oil are used as lubricants.

For Gears: Lubricants in gears are under very high pressure or load so the

lubricants must have good adhesive properties i.e. must remain stick to the

gear teeth and must not be removed by centrifugal force a rotating gears.

The lubricant should have

1. Good oiliness

2. Have high load carrying capacity thus thick mineral lubricating oil

containing extreme pressure additive such as organic compound of

chlorine sulphur and phosphorous are used for where lubricants.

For cutting tools

Cutting includes turning, grinding, machining etc. of metals. In this process

the cutting tool is continuously exposed to the fresh underline metal. This

causes high rubbing resulting in generation of large amount of heat. The

liberated heat may over heat the tool and may damage it, cause imperfect

108

cut, and also increase. The power consumption (because of friction).

Therefore the main functions of cutting fluids are to cool the tool. For light

cutting oil emulsion are used and for heavy cutting, cutting oils essentially,

minerals oil of low viscosities with some additives like fatty oils, chlorinated

compounds and sulphurized fatty oils are added.

For Internal combustion engines

In internal combustion engine, the lubricant is to be exposed to high

temperatures. Therefore, the lubricant, should posses high viscosity index

and high thermal stability. It should not evaporate or decompose at the

operating high temperatures. The petroleum oils containing additives, which

impart high viscosity index and oxidation stability to them, are used as

lubricants for internal combustion engines.

For transformer

The function of a lubricating oil in an an electrical transformer is to insulate

the windings and to remove heat generated, when the transformer is

subjected to on load. The lubricant used for these transformer should posses

low viscosity and good dielectric properties. When transformer oil exposed

to air,high temperature,electrical stress and catalytic influence of copper

cause various chemical changes in the oil causing to formation of acid as

well as sludge. To remove the formation of acids and sludge, highly refined

mineral oil having high insulating properties, optimum oxidation resistance

and high chemical stability are used .

Q. Explain fluid film (thick film) lubrication

OR Explain hydrodynamic lubrication.

Ans: Fluid film lubrication: This type of lubrication is used in machines

working at low pressure and high speed

In this type of lubrication, the moving or sliding surfaces are separated from

each other by a thick film of fluid (10000A thick), so that surface to surface

contact and welding of junctions rarely occurs

109

1. In this method the liquid lubricant is introduced in between the moving

surfaces.

2. The lubrication film covers or fills the irregularities of moving or sliding

surfaces and forms thin layer in between them

3. This thin layer avoids metal to metal contact and reduces the friction

4. The resistance in the movement of two moving surfaces is due to internal

resistance of the lubricant particles moving each other. Thus lubricant

should have minimum viscosity

Uses: This type of lubrication is provided in case of delicate instrument and

light machines like watches, clocks, guns, sewing machines, scientific

instruments.

Q. Explains thin film (boundary) lubrication.

OR

Explain the lubrication, which is present in heavy machineries which

are having low speed & high pressure on it.

Ans: This type of lubrication is used

110

a. When continuous fluid film of lubricant cannot persist i.e. viscosity of oil

lubricant is very low & direct metal to metal contact is possible

b. The machine parts work under low speed & heavy load

c. A shaft moving from rest

In this type of lubrication:

1. A thin layer of lubricant is adsorbed by physical or chemical forces on

both the metallic surfaces

2. These absorbed layer cannot be removed easily & avoid direct metal to

metal contact

3. For boundary lubrication the lubricant molecule should have long

hydrocarbon chains, lateral attraction between the chains, high viscosity

index, good oiliness resistance to heat and oxidation

4. In this type of lubrication graphite, molybdenum disulphide with oil ,

vegetable oil, animal oil and their soaps are used

5. This type of lubrication is used for tractor, rollers, lathe machine etc.

111

Q. Explain extreme pressure lubrication

Ans: This type of lubrication is used when the moving parts of machine work

under very heavy load or high pressure & high speed, due to this the

lubricant may decompose.

1. For these conditions, some additives are added to lubricants. These additives

are called as “extreme pressure additives”

2. The additives are reactive compounds of phosphorous, sulphur etc

3. At a very high temperature, they as react with metal & convert as sulphide or

phosphates

4. These lubricants have very high melting points & acts under extreme

pressure lubrication conditions

5. In this type of lubrication sulphurised oil, chlorinated wax are used

This type of lubrication is used for gears, cutting tools, wire drawing of

titanium etc

112

Q. Differentiate between fluid film lubrication and boundary lubrication

Ans :

Fluid film lubriacation Boundary lubrication

1. Lubricants having low viscosity are

used in fluid lubrication

1. Lubricants having high viscosity are

used

2. Thickness of oil film is more than

10000C

2. Thickness of oil film is less than

10000A

3. These are used in the machines

working under high load and high

speed

3. These are used in the machines

working under heavy load and low

speed

4. These are sued as such. No metallic

surface is required for adsorption

4. The thin lubricating oil is adsorbed

by physical or chemical forces

5. Watches, clocks, guns, sewing

machines require fluid film

lubrication

5. Gears, rollers, tractors, etc. require

thin film lubrication

113

Chapter - V

ENVIRONMENTAL CHEMISTRY

Q. Define air pollution

Ans : Air pollution is defined as an undesirable change in physical, chemical or

biological characteristics of atmosphere causing harmful effect to human,

plants and animal life.

Q. Define Pollutant (air pollutant)

Ans The solid, liquid or gaseous substance present in such a large concentration

that are hazardous to the environment and harmful to life

OR

A pollutant defined as an unwanted/undesirable foreign matter added to the

environment which causes pollution

Q. Define water pollution

Ans : Water pollution is defined as any change in the physical, chemical and

biological properties of water as well as contamination with foreign

substances which decreases the utility of water.

Q. Describe the various sources of air pollutant and discuss their

effects.OR Give sources, effect of oxides of sulphur, carbon, nitrogen,

dust, smoke, smog, lead dust, asbestos dust.

On the basis of physical state the air pollutants are classified

A. Gases

Gases are freely mincible with air, without setting down.

Following are the gaseous air pollutants

B. Particulates

Particulates include dust, smoke, smog, asbestos dust , lead dust etc.

114

Pollutant Sources Effects

i. Sulphur

dioxide

(SO2)

Thermal power plants

Petroleum industry

Oil refineries,

Sulphuric acid plants

Sulphide ore roasting

plants

It cause cardiac (heart)

respiratory disorders like

asthma, bronchitis etc

Also causes eye irritation,

thorat troubles

Causes damage to agriculture

Corrosion of metals

Affects photynthesis of plants

ii. Sulphur

trioxide

(SO3)

Obtained by oxidation

of sulphur dioxide

under sunlight

In presence of water

SO2 and SO3 are

converted in to H2SO3

and H2SO4 and causes

acid rain

It causes irritation of

respiratory trac.

Destructive to vegetation

Acid rains affects various

materials, causes corrosion of

marble, iron and steel.

Desructive to lung tissues

It may cause heart failure

iii. Carbon

monoxide

(CO)

Obtained by partial

combustion of fuel in

automobiles, industries

and oil refineries,

smoke from cigarette,

bidi

It causes headache, visual

difficulty, paralysis and even

death in the human beings

It reduces oxygen carrying

capacity of blood due to

formation of

carboxyhaemoglobin

It also leads to llaziness,

exhaustionof body. Headache,

and serious effects on

cardiovascular system

iv. Carbon

dioxide

(CO2)

Obtained by burning of

fuels such as coal,

wood etc, respiration of

plants, animals and by

deforestation

Increase in CO2

It is non poisonous, non

corrosive and too much in

atmosphere causes pollution,

Respiratory disorders and

suffocation

115

percentage by 10-15%

in air causes rise in

temperatur by 0.50C

v. Nitrogen

oxiden (NO,

NO2)

Produed from

combustionof fueld

(Coal, disel, petrol)

acid manufacture

explosive industry,

acid pickline plants

It causes respiratory illness

among children , leads to

irritation of eyes and even

lungs congestio.

It combines with

hydrocarbons to form smog

which

i. Limits visibility of roads

and may cause accidants.

ii. Causes eye irritation

iii. Difficulty in breathing

asthma, and bronchitis

C. Particulates

Particulates include dust, smoke, smog, asbestos dust , lead dust etc.

Particulates Sources Effects

i. Dust From mines, quarries,

furnaces, power, houses,

vehicular, traffics, house

cleaning dust, pottery and

ceramics factory stacks,

agriculture, combustion

operations etc

It causes allergy and

respiratory diseases

If dust contain silica it

causes silicosis

It also causes corrosion

and soil erosion

ii. Smoke Obtaied by incomplete

combustion of fuels or

from chemical reactions

Major sources are roads

locomotives, diesel

engines, automobile petrol

Loss of calorific value due

to incomplete combustion

Possibility of cancer

disease

Spoiling of clothing, rags,

exterior finish of

116

engines, furnaces hearths

etc

buildings

iii. Smog It is the combination of

smoke and fog

It is a natural phenomenon

in which liquid particles

remain suspended in air

Smog has same effects as

smoke, but some what

prolonged one

iv. Lead dust The main source in lead

mining and smelting

works, lead batteries, lead

base alloys, automobile

exhausts

It causes lead poisoning as

it settles down on plants

and food stuffs

v. Asbestos

dust

The main sources are mining,

processing and manufacture

of asbestos sheets and ropes

used in

automobiles,buildingsflooring

and insulating materials

It causes asbestosis

disease (lungs disease),

cancer etc.

Q. Write in brief, various methods of controlling air pollution

Ans: The best way, „to control air pollution is to prevent or reduce the formation of

pollutants at the source itself.

Automobile emission can be minimized by using catalyst. Which

helps in cleaning the exhaust gases

Tall chimneys reduce the concentration of air pollutants at ground

level

Dust: Following methods are used to remove dust

a. Extraction ventilation is applied for removal of dust

In this air stream carrying suspended dust particles is first maintained at a

sufficient velocity to keep the dust particles in suspension, thereafter, the

117

rate is reduced suddenly, so that the dust paticles settle down in a setting

chamber.

b. Cyclone collector

Gas containing particulates is allowed to flow into a tight circular spiral

fitted chamber. The centrifugal force, forces particulates to move towards

the walls of chamber from where they start settling down due to force of

gravity. The particulates collected at the bottom of the chamber are removed

periodically from the bottom.

Smoke

Smoke is a colloidal solution of negatively charged carbon particles in air.

Smoke when passed through cottrell electrostatic precipitator which is

provided with a knowb maintained to a very high voltage for + 30,000

volts. The negative charges of carbon particles from smoke are rubbed off

and they are precipitated out at bottom and only hot dust free gases go out

through the upper outlet towards chimmney.

Smoke can also be reduced by

a. Correct firing method

b. Admitting correct quantities of air.

c. Maintaining high temperature during combustion. At low temperature

combustion is incomplete and smoke is produced.

d. Feeding the fuel continuously

Sulphur dioxide (SO2) pollutant can be removed by chemical

treatment

a. Lime water wash The gases containing SO2 are passed through lime

water as a result SO2 will removed as sillicate

b. By liquid ammonia SO2 gas is passed through ammonia, when

ammonium sulphite is obtained.

Cairox methodThe oxidation of SO2 takes place when SO2 is mixed with

alkaline KMnO4 solution through spray.

118

The use of wood and coal as a fuel should be gradually reduced and

modern energy sources like electricity, tidal power and solar power

should be used for domestic as well as for industrial purposes..

Acids and chemical fumes

By passing gases/vapours through a tower filled with coke and by

passing the counter current of water in the reverse direction.

Zoning: Proper industrial zoning can reduce air pollution. It should

have buffer zone, which separates houses and industrial units.

Forestation : Due to deforestation the level of CO2 will reduce and

also problem of global warming

Q. What is meant by deforestation? What are the causes, effects of

deforestation. Write control (preventive) measures.

Ans : The destruction of forest due to indiscriminate cutting of trees and causing

deterioration of environment is called as deforestation

Following are the causes of deforestation

Population explosion: A tremendous increase in population increased

the demand for forest products like fire wood, timber etc. and also

cleared the fire wood and for human settlement Ex. : agriculture, housing,

roads, factories, railway tracks etc.

Forest fires due to natural calamities and some human activities.

Forest pests, insects destroy trees by eating up leaves etc.s

Some natural forces floods, storms, snow etc. damages forests

Excessive grazing of animals

The effects of deforestation are as follows

Destruction of wild habitat

Increase in soil erosion

Decrease in oxygen level

Decrease in availability of forest products

It reduces water level and may increase the frequency of droughts

Also causes global warming, as CO2 level increases

119

The following measures should be taken for conservation of forest

Instead of fire wood, some alternate sources of energy such as

biogas, solar energy should be used as a fuel.

Over grazing and deforestation should be prohibited

Plantation of trees i.e. afforestation should be done on deforested

areas.

Pest and forest fire should be controlled by modern techniques

Forestry can be improved by using modern techniques like use of

fertilizers, irrigation, weed control, tissue culture etc.

Q. What is ozone Layer depletion? Write its causes, effects and preventive

(control) measures.

Ans : Ozone is produced in the upper layer of atmosphere above 20 km from the

earth surface. Oxygen from air is converted to ozone due to action of U.V.

rays

3𝑂2

𝑢𝑣 𝑙𝑖𝑔 𝑕𝑡 2𝑂3

Oxygen ozone

Importance of ozone layer

Ozone layer is a protective layer, which strongly absorbs U.V. radiations

from the sun and protects the life on earth from severe radiation damage.

Ozone layer is depleted then the harmful u.v. radiations from the sun would

reach the earth surface affecting the life of living beings

Following are the causes ozone depletion

i. Chlorofluro carbon (CFC) are used in air conditioners, refrigeraters,

propellants, in aerosol of sprays, in thermocole causes destruction of

ozone in the stratosphere.

CFC molecules escape into the atmosphere and undergo

decomposition under the influence of u.v. radiations, to give chlorine.

Each atom of chlorine so released reacts with ozone molecules and

converts ozone into oxygen.

120

Thus ozone depletion takes place gradually and u.v. rays absorption

capacity of ozone layer decreases slowly.

𝑂3

𝑕𝑟 𝑂2(𝑔) + 𝑂

𝐶𝑙 + 𝑂3(𝑔)

ClO + O2(g)

𝐶𝑙𝑂 + 𝑂 Cl + O2(g)

The chlorine atom produces above causes as a chain reaction

ii. Due to volcanic activity in the earth, the chlorine is released in the

atmosphere and due to reaction with nitric oxide, atomic oxygen,

reactive hydroxyl radical causes the ozone depletion

O3 + NO NO2 + O2

O3 + O O2 + O2

O3 + HO HO2 + O2

HOO- + O

HO

- + O2

The effects of ozone layer depletion are as follows

i. As the ozone layer is depleted, the weak ozone layer allows more

u.v. radiations to reach the earth. u.v. rays are harmful to living

things. They cause skin cancer, swelling of skin, sun burns, burning

sensation, skin ageing, leukemia, breast cancer cataracts of eyes,

edema, hemorrhage, lung diseases, visual impairment, premature

ageing, DNA, breakage etc.

ii. Ozone enters in plants which cause visible damage to leaves, reduce

photosynthetic rate, it reduces the yield of the plants and also

damages food production

iii. They affect the ecosystem badly

iv. They reduce the population of aquatic species

Following are the control measures of ozone layer depletion

i. Discourage the use of ozone depletion gases like CFCs, Nox,

halogens and other gases.

ii. In refrigeration, instead of freon other coolant, like helium should be

used

121

iii. Reforestation and forest preservation is necessary.

Q. What is sewage and sewage water? What are the main objectives of

sewage treatment? Describe sewage treatment.

Ans : Sewage: It is liquid waste, which contains human and household waste

water, industrial waste, ground wastes and storm water.

Sewage water: The water which contains organic matter, human excreta and

domestic waste, microbes, house hold waste is called sewage water.

Main objectives of sewage treatment

1. To render sewage in offensive so that it causes no odour or nuisance.

2. To reduce or eliminate danger to the public health by possible

contamination of water supplies (like river, canal etc.) and bathing areas

(e.g. pond, etc.).

3. To prevent the destruction of fish or other aquatic life in river, canal etc.

into which

4. Sewage discharge is generally made.

5. Sewage treatment is generally carried out using the artificial treatment

method.

The basic features of sewage treatment are

1. To reduce the solid contents of sewage

2. To remove all nuisance causing elements and

3. To change the character of the sewage so that it can safely be discharged

into the natural water course such as river or applied on land

The steps involved in sewage treatments are as follows

1. Preliminary process

2. Settlement process

3. Biological process

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Preliminary process Causes removal of large and coarse solid, inorganic

matter suspended or floating in the sewage. This involves in passing the

sewage through bar screens (to remove large suspended and floating matter)

and mesh screens (to remove coarse, solids, gravels, silt )

Settlement process

This process removes greater portion for suspended inorganic and organic

solids from the liquid sewages. For this continuous flow type‟ sedimentation

tanks are employed. Chemical treatment is „sometimes‟ given to sewage just

prior to sedimentation. This results more rapid and complete removal

suspended matter. The chemicals employed are alum, ferrous sulphate etc.

These produce large gelatinous flocks which entrap finely divided organic

matter and settles rapidly.

Al2 (SO4)3 + 6H2 O Al (OH)3 + 3H2SO4 at P

H 7.5

The chief virtue of adding chemical coagulant is its ability to remove

colloidal material.

Biological process

It is an essentially an „aerobic biochemical oxidation‟ or aeration. In this

process sewage water is filtered through specially designed sprinkling filters

so that aerobic conditions are maintained all the times. During this aerobic

oxidation process the carbon of the organic matter is converted into CO2, the

nitrogen into NH3 and finally into nitrites and nitrates. The dissolved bases

present in the sewage water then forms salts such as ammonium nitrate,

ammonium nitrite, calcium nitrate

NH2CONH2 𝑜𝑥𝑖𝑑𝑎𝑡𝑖𝑜𝑛 (𝑎𝑒𝑟𝑜𝑏𝑖𝑐 ) CO2 + 2NH3

NH3 𝑜𝑥𝑖𝑑𝑎𝑡𝑖𝑜𝑛 HNO3, HNO2 etc

HNO3, HNO2 +𝐵𝑎𝑠𝑒 NH4NO2, NH4NO3, Ca(NO2)2, Ca(NO3)2, KNO2 etc

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Q. Explain four major sources causing Air Pollution

Ans : Major sources causing Air pollution are

A. Gases

Sulphur dioxide (SO2) : Thermal power plants, Petroleum industry, Oil

refineries, Sulphuric acid plants, Sulphide ore roasting plants

Sulphur trioxide (SO3) : SO3 is formed by the oxidation of SO2 under the

influence of sunlight

Carbon Monoxide (CO) : Partial combustion of fuel in automobile,

industries and oil refineries, cigarette and bidi, smoke and domestic heat

appliances

Carbon dioxide (CO2) : It is released in the atmosphere in the form of

smoke by burning of fuels eg coal gases, It is also released into air by the

respiration, plants and animals, It also occurred by deforestation

B. Particulates

Dust: Mines and quarries, Furnaces, Power houses, Vehicular traffics, house

cleaning dust. Poultry and, Ceramic factory, Agricultural forest fires, Natural

winds, Earth movements, Rubber tyre abrasions

Smoke: Rail roads, Locomotives domestic wood, coal grates, industrial

power plant, open fires refuse, incinerators, diesel engines, automobile,

gasoline engines, furnaces, hearths etc

Smog: Due to the action of sunlight on hydrocarbons coming largely from

vegetable matter and the nitrogen oxides emitted by factories and car

exhaust along with CO2, CO, and unburnt hydrocarbon particles and also

SO2.

Lead dust: Automobile emissions, Lead smelters, Burning of coal or oil,

Lead arsenate particles, Lead batteries, and paints and manufacture of lead

based alloys.

C. Deforestation: Green plants use CO2 for the manufacture of food by

photosynthesis and give out O2 there by purifying the atmospheric air

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plants also control H2S, HNO3 and chlorine. Thus plants help in

controlling the air pollution. Excessive cutting of trees consequently

cuases indirectly air pollution.

D. Radioactive gases

The radio active elements which occur in rocks and soils are derivatives of

uranium (U) They (Th) and actinium (Ac) series.

They evolve radioactive gases which mainly consists of radon and threon.

These gases are harmful to human health

Q. What are causes (Sources) of water pollution?

Ans : Causes of Water Pollution are

1. Industrial waste: Water gets polluted by industrial effluents containing

acids, alkalis, soaps, detergents, pesticides, insecticides, fungicides and

metals like Cu, Zn, Pb, Hg etc. which are released from chemical

industries.

2. Domestic Sewage: It includes human and household waste waters,

municipal waste etc. directly mix into canals and rivers cause pollution of

river water. When sewage is discharged into a stream of water directly

into river lakes.

3. Suspended Particles

The surface water containing bacteria, algae, viruses make water unfit for

domestic and industrial purposes. High concentration fo organic and

inorganic solids, sand, precipitates, insects, ores, fine particles of soil are

added to river and cause water pollution.

4. Spilling of Oil : Pollution of oceans about one million tones of oil is

spilled into the ocean each from shipping and drilling operations. Oil

from oil mills and washing of automobiles pollute the rivers.

5. Drain from land and fields: Residual insecticides, pesticides and

fungicides are washed down into lakes, streams, rivers etc. and pollute

them.

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6. Fertilizer: Wastes from fertilizer plants containing nitrates, phosphates ,

ammonia etc. are released in water and causes pollution.

7. Atomic explosion: Atomic explosion and processing of radioactive

materials near the sources of water causes water pollution.

Q. What is green house effect? Name Green house gases? How is takes

place?

Ans : Definition: The green house effect may be defined as “ The progressive

warming up of the earth‟s surface due to blanketing effect of manmade CO2

in atmosphere”.

The four major green house gases which cause adverse effects are

carbondioxide (CO2), methane (CH4), nitrous oxide (N2O) and chlorofluoro

carbons (CFC‟s). The other gases like ozone, SO2 also cause the same global

warming.

The heat received from the sunlight heats up earth and some of it is radiated

back into space after absorption but certain gases present in the lower

atmosphere acting like a glass in a gren house allow radiations in the range

300-2500 nm. While filtering u.v. rays in the range <300 nm. It however

does not allow the earth to reradiate heat in to space. Thus a green house is

that body which allows the short wavelength incoming solar radiation to

come in but does not allow the long wave outgoing terrestrial infrared

radiations to escape. A part of the heat so trapped in these atmospheric gases

is re-emitted to the earth‟s surface.

The net result is the heating of earth‟s surface by this phenomenon called the

green house effect.

Q. What is global warming? Write consequences/impact/effect of green

house effect? Write Control and Remedial Measures of Green House

Effect. OR Global warming is warning for us. Justify the statement

Global Warming: The increase in the temperature of earth surface due to

the effect of greenhouse gases is called as global warming

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Consequences/impact/effect of green house effect (Global warming)

Due to rise in temperature of the earth, the oceans get warmed up

rising sea level and flooding low lying regions. Slight increase in sea

level makes considerable effects on habitation patterns because the

coastal cities and ports come under threat of floods.

There will be heavy increase in rain fall, causing the soil erosion

rapidly. This results in desertification and drought.

The tropics wetter and the sub tropics which are already dry will be

moe dried. In temperature regions the winter will be shorter and

warmer and the summer will be longer and hotter.

e.g. North America

Plants and animal life will also be affected resulting in disruption of

the whose ecosystem

The rise in temp may cause climatic change leading to more

cyclones and hurricanes and also melting of snow in mountains

causing more floods during monsoon

Global warming can affect the world‟s food production

Due to melting of ice at polar region the water level may rise and

may submerge the coastal area

Natural calamities like Cyclones, Hurricane, Typhoons and Tsunami

may occur frequently and strongly

Control and Remedial Measures of Green House Effect (global warming

1. Reducing the consumption of fossil fuels (coal and petroleum). This can

be achieved by depending more on non-conventional renewable sources

of energy like wind, solar, nuclear and bio-gas energy.

2. Deposing elsewhere the formed green house gases instead of releasing

in the atmosphere.

3. Enhancing forestation will reduce the CO2 level and thereby decreasing

green house effect.

4. International cooperation for reducing green house gases.

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Q. Explain air pollution due to IC engine (automobile). OR Explain how

I.C. engine responsible for pollution. Give the method of controlling to

Auto Emission

Ans : The internal combustion engine used for running motor car, buses, planes,

trucks, auto rickshaws, scooters etc. when fuel like kerosene, diesel, petrol is

burnt a lot of smoke is released into the atmosphere. A major cause of air

pollution is various type of auto vehicles. These fuels are all mixture of

hydrocarbons of different molecular masses and out of this octane

constituent major component of fuel. When it burns in IC engine reaction

takes place

2C8H18 + 25 O2

16 CO2 + 18H2O + Heat

Besides the pollutant CO2, CO, SO2, hydrocarbons acids, alcohols, NO2 etc.

enter the atmosphere. These gases effects on human being

Control of air pollution due to IC engine

1. By using engine with better design for higher efficiency. Due to this,

maximum fuel is burnt and less amount of unburnt fuel, carbon

monoxide, hydro-carbons etc. are released

2. By supplying sufficient amount of fuel and more amount of air (O2) so

that complete reaction takes place

3. By improving quality of gasoline by adding tetra-ethyl-lead (TEL). This

reduces the amount of smoke

4. By using suitable catalyst in the fuel so that complete oxidation of fuel

takes place controlling pollution

Q. Write any preventive (control) measure of water pollution OR How is

water treated?

Ans Preventive (control) measure of water pollution

1. Stabilization of the ecosystem: Ecosystem stabilization is the most

scientific method which involves reduction of waste at source, trapping

nutrients, fish management, aeration, harvesting and removal of biomass.

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2. Re-utilization and recycling of the waste: Waste water is given sort of

treatment before discharging into rivers, lakes, ponds etc. Such treated

water can be recycled and reused to generate cheaper fuel, gas and

electricity.

3. Oxidation method (or stabilization of ponds) : Waste water is stored in

large and shallow ponds. In presence of sunlight and organic nutrients in

waste, large number of bacteria grows very fast into harmless simple

compounds. This waste can be reused for irrigation of land without any

danger of pollution

4. Waste water reclamation: The sewage water is given treatment and

directly used for irrigation and fish farming.

5. Use of chemicals: Sewage on effective filtration followed by

chlorination provides water safe for drinking and domestic use.

6. Use of Bioreactors: Organic dirty sewage and factory waste is pumped

into the bioreactors which removes about 95% of impurities. Even

corrosive acids, alkalis, and industrial effluents can be purified using

bioreactors. They neither produces odorous smell nor toxic by products

during the reactions

7. By avoiding washing clothes, utensils, cattle and vehicles directly in

river/canal water.

Q. Give names of environmental segments. Describe in brief.

The environment consists of following four segments.

1) Lithosphere 2) Hydrosphere 3) Atmosphere 4) Biosphere

Lithosphere:

The mantle of rocks constituting the earth crust is called lithosphere.

For practical purpose the soil covering the rocks (which results from

physical, chemical & biological process during whethering). It is also

considered to be an important part of the lithosphere.

The soil mainly consists of complex mixture of organic, inorganic matter

and water.

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It consists of biologically active components such as polysaccharides,

nucleotide and organo sulphur compounds, sugar and humid materials,

The clay minerals and humus present in the soil possess a very high cation

exchange capacity and thus help in supplying essential trace metals to the

plants as nutrients.

Hydrosphere:

This includes all the surfaces and ground water resources i.e. ocean, seas,

rivers, streams, lakes, ground water and the water locked in rock cervices

and mineral lying deep below the earth crust.

Earth is called blue planet because 80% of its surface is covered by water

but however 97% of the earth water resource is locked up in the ocean and

seas, which is too saline to drink and for direct use for agricultural and

industrial purpose.

Water exhibits unusual properties, as compared to the hydrides of V1 group

elements, due to the presence of hydrogen bonding.

Without hydrogen bonding, water would have boiled at -1000C and in that

case life on earth would have been impossible.

Because of hydrogen bonding water is a liquid at room temperature, with

melting point 00C and boiling point at 100

0 C at atmospheric pressure.

Biosphere:

This is the region of the earth where life exists and includes a global girdle

extending from about 10,000 m below sea – level to 6,000 m above sea –

level.

Thus the biosphere covers the entire living organism and their interaction

with other segments of the environment namely the lithosphere, the

hydrosphere and atmosphere.

Atmosphere: The atmosphere comprises of a mixture of gases (N2,O2,CO2)

and it extends upto about 500km above the surface of the earth.

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Biosphere : Atmosphere : Hydrosphere

1 : 300 : 69,100

A constant exchange of matter takes place between the atmosphere,

biosphere and hydrosphere.

It plays a key role in maintaining heat balance of the earth.

As it absorb most of the cosmic rays from outer space and helps in

sustaining life on the earth.

The important gaseous constituents of the earth i.e. O2,N2 and CO2 play

important roles in sustaining life on the earth.

Oxygen support life on earth, nitrogen is an essential macro- nutrient for

plants and carbon dioxide is essential for photosynthetic activity of plants.

Q. Describe the structure of Atmosphere

Ans : The atmosphere which extends upto about 500 km, can be broadly divided

into four major regions, with widely varying temperature even within the

region.

1. Troposphere

2. Stratosphere

3. Mesosphere

4. Thermosphere

Troposphere

This region is nearest to the earth surface and contain 70% of mass of

the atmosphere.

The troposphere contains the major components such as nitrogen,

oxygen, carbon dioxide, water and particulate matter also.

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The troposphere is a turbulent region due to the global energy flow

arising from differential heating and cooling rates between equator and

poles.

The density of air in this region, decreases exponentially with increasing

altitude.

The troposphere contains most of the water cloud and particulate matter

of the atmosphere.

The temperature of air in the troposphere decreases fairly steadily with

increasing altitude from ground temperature to a temperature of about -

560C.

The temperature altitude curve then changes its slope rather suddenly in

a narrow transitional layer at the top of the troposphere known as the

tropause.

Stratosphere

The region above the tropopause is called the stratosphere.

In this region, the temperature altitude curve shows a warming trend

with increasing altitude.

The temperature in this stratospheric region continues to increase with

height, untill 50 kms where the temperature attains a maximum of -20C.

This warming up tendency in the stroposphere is due to the absorption of

solar U.V. radiation by ozone.

Ozone is the major chemical species in this region which absorbs

ultraviolet rays causing rise in temperature.

O2 + h𝜐 → O + O

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Thus by absorbing these rays stratosphere act as a protective shield for

life on earth.

If some impurity molecules are injected in stratosphere act as a

protective shield for life on earth.

If some impurity molecules are injected in stratosphere they can cause

long term global harzards.

The region immediately above the stratosphere is called “stratopause”.

Which is second transitional layer that is relatively warm.

Mesosphere

This is the region above the “stratopause” and extends upto 85 km

height.

In this region the temperature again decreases with height.

This is due to relatively low level of ozone and other species that can

absorb U.V. radiation from the sun.

The temperature at the top of the Mesosphere reaches about 920C.

Immediately above the Mesosphere is another transitional layer called

“Mesopause” which is the region of minimum or coldest temperature in

the atmosphere (i.e. about -1000C).

Thermosphere

This is the region immediately above the mesopause, where the

temperature rises very rapidly with increasing altitude.

The maximum temperature that is attained in this region is about

12000C.

This region is characterized by low pressures and low densities.

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The atmospheric gases present in this region absorb the solar radiations

in the far ultra-violet region and undergo ionisation.

The region above stratosphere, in the altitude range of 50km to 100 km

is called Ionosphere.

In this region positive ions e.g. O2+, O, NO

+, .and electrons exist at

significant levels.

Q. Give sources, causes, effect and control (preventive) measures of Acid

rain

Ans : Sources: Emission from volcanoes and form biological processes that occur

on the land. Industrial factories, power generating plants and vehicles.

Causes of acid rain: It is due to the dissolved oxides of sulphur and

nitrogen. The gases like SO2 and NO from industries dissolves in water and

form respective acids.

SO2 + H2O → H2SO3

2SO2 + O2 → 2SO3

SO3 + H2O → H2SO4

2NO2 + H2O → HNO3 + HNO2

Effects of acid rain:

1. Acid rain makes the soil more acidic thereby reduces the fertility of the

soil.

2. It affects the growth of crops, plants etc.

3. It affects the survival of fishes and reduces the population of aquatic

species.

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4. It badly makes damage to buildings, vehicles, structural materials etc.,

5. It affects human being‟s life systems and organs like skin, lungs and

hair.

6. It damages the memorable monuments, buildings etc., The famous „Taj

Mahal‟ is being affected severely.

7. Damage valuable ancient sculptures, carved from marble, limestone,

sand stone etc

Ex. In Greece and Italy valuable statue are damaged due to acid rain.

Preventive measure:

1. The only practical approach to counter the problem of acid rain is to

reduce SOx and NOx emission. The following three general options are

considered for this purpose.

2. Energy conservation- Resulting in reduced fuel consumption and hence

slower emissions of Sox and NOx conservation via more efficient fuel

use and through improved thermal insulation is also being studied.

3. Desulphurization and gentrification of fuels of stack gases and increased

use of fuels naturally low in sulphur content or use of technologies that

reduce the Sox and NOx emission desulphurization and use of low NOx

producing technologies are the only viable control option today and will

perhaps continue to be so for some more time.

Q. Define soil (land) pollution. Give causes (sources) and control measures

of soil pollution

Ans : Soil pollution is defined as the addition of some chemical substances in large

proportion to soil due to which fertility of soil get affected

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Sources (causes) of soil pollution

1. Industrial waste: it consist of waste from paper, chemical, sugar, textile

industry which in solid, liquid or gaseous forms and which contains

harmful chemicals.

2. Urban waste: This consists of waste like plastics glasses, metal cans,

and other discarded materials. All these materials cause soil pollution.

3. Agricultural pollutant: It includes chemical fertilizers which are carried

away by rain water and get concentrated in low region.

4. Biological pollutants: It includes large quantity of human and animal

waste. Particularly the pathogenic germs are absorbed by soil and may be

retained for longer period.

5. Chemicals like fertilizers, pesticides, bactericides applied to plant and

soils.

6. Radioactive wastes discharged from industrial and research centres.

7. Soil get polluted by the removal of it‟s upper fertile layer.

8. Improperly disposed human and animal waste.

9. Radioactive waste discharged from industrial and research centers.

10. Soil erosion due to deforestation over grazing, unplanned irrigation and

defective agricultural practice.

Control measure of soil pollution:

1. To avoid contamination of industrial waste with soil. It is necessary to

treat these wastes properly and reduce their chemical reactivity.

2. To control the use of chemical fertilizer and pesticides and replace them

by bio- fertilizer

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3. To cover the untreated biological waste materials with soil and provide

absorption sites for liquid waste after treatment.

4. Industrial and sewage waste should be properly treated beforedisposal

on land.

5. Using sanitary landfills.

6. By forestation.

7. Avoiding throwing away solid waste like garbage, ash, sludge, building

material empty bottle

Q. Give sources, effect and control measures of radioactive pollution OR

Explain pollution due to radioactive elements

Ans : Sources:

1. One of major source is nuclear explosions i.e. U235

or Pu239

etc. In

addition radioactive rays may be emitted due to in improper shielding.

2. Industrial, medical and research use of radio- active materials.

3. Radioactive ores processing industries may cause emission of

radioactive elements or rays due to natural radio- activity.

Effect (Disadvantages) of radioactive pollution:

1. The radio isotopes affect upon chromosomes and bring about genetic

disorder.

2. These cause mutations in genes which passes from one generation to

another leading to skin cancer.

3. This may produce permanent damage to living organisms which may

lead to death.

4. These radiations are penetrating which can cause breaking up of organic

molecules present in our body.

137

Preventive measure:

1. Steps should be taken to prevent the leakage of radioactive element from

nuclear reactors.

2. The radioactive waste should be stored at such places, where they

gradually decay to their final stable product.

3. Methods to be adopted for the safe handling and disposal of radioactive

materials.

Q. Define Noise pollution. Give sources (causes), effects (impact) and

control measures

Ans : Noise Pollution : It is an increased amount of sound which is painful to

listen and causes ill effect on life.

Noise level is expressed in decibel (dB)

Sound above 80decible is said to be noise.

Sources of Noise pollution:

1. Transportation:

Number of vehicles running on road like buses, trucks, tractors, cars

two wheelers and particularly the diesel engine vehicle causes noise

pollution

Noise pollution is due to air traffic depends upon type of air craft the

number of flights and flight paths.

Railway traffic causes noise due to vibration during operation which

increases with the speed.

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2. Industrial Noise:

Different machines operating on electricity diesel or coal produce

noise.

Electric motors, impact machines, compressors etc. produce higher

noise.

Heavy machine producing at high speed and greater load cause

greater noise pollution.

3. Neighborhood noise:

Use of loud speakers in public functions, religious processions

festivals etc is a common feature today.

Due to which Educational institutions, hospitals, offices are disturbed

to a great extent due to such noise.

4. Noise in buildings:

Apartment is often annoyed by noise in their homes, especially when

the building is not well designed and constructed.

In this case internal building noise from plumbing, boilers, generators,

air-conditioners and fans can be audible and annoying

5. Construction Noise:

The noise from construction of highways, city streets and buildings is

a major contributor to the urban scene. Construction noise source

includes pneumatic hammers, air compressors, bulldozers, Loader,

dump trucks.

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Effect of noise pollution:

1. Physiological effects: The physiological features like breathing

amplitude, blood pressure, heart-beat rate, pulse rat, blood cholesterol

are affected.

2. Loss of hearing: Long exposure to high sound levels cause loss of

hearing. This is mostly unnoticed, but has an adverse impact on

hearing function.

3. Human performance: The working performance of workers/human

will be affected as they will be losing their concentration.

4. Nervous system: It causes pain, ringing in the ears, feeling of

tiredness, thereby effecting the functioning of human system.

5. Sleeplessness: it affects the sleeping thereby inducing the people to

become restless and lose concentration and presence of mind during

their activities.

6. Damage to material: The buildings and materials may get damaged

by exposure to infrasonic/ultrasonic waves and even get collapsed.

Control of Noise pollution:

1. Reducing the noise levels from domestic sectors: The domestic

noise coming from radio, tape recorders, television sets, mixers,

washing machines, cooking operations can be minimized by their

selective and judicious operation.

2. Maintenance of automobiles: Regular servicing and tuning of

vehicles will reduces the noise levels. Fixing of silencers to

automobiles, two wheelers etc., will reduces the noise levels.

140

3. Control over vibrations: The vibrations of materials may be

controlled using proper foundations, rubber padding etc. to reduce the

noise levels caused by vibrations.

4. Low voice speaking: Speaking at low voices enough for

communication reduces the excess noise levels.

5. For controlling sound pollution, in buildings absorptive materials such

as porous bricks, acoustic tiles etc can be used.

6. Installing noisy machines in sound proof chambers.

7. Covering noise – producing machine parts with sound absorbing

materials to check noise production.

8. Planting green trees and shrubs along roads, hospitals, educational

institutions etc help in noise reduction to a considerable extent

9. Prohibition on usage of loud speakers in the habitant zones except for

important meetings/functions.

10. Proper lubrication and maintenance of machines, vehicle etc. will

reduce noise levels.

11. Setting industries away from the residential area

12. Using cotton plugs or ear muffs

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Chapter VI

ELECTROCHEMICAL ENERGY SYSTEM

Q. Explain basic concept in battery technology

Ans:

1) Cell: “A cell is a device in which either electrical energy is converted to

chemical energy or chemical energy is converted to into electrical energy.”

2) Battery:“Battery is a device in which many cells are connected in

series.”

3) Charge (Charging):“This is the operation of a cell when an external

source of current reverses the electrochemical reaction of the cell to restore

the battery to its original state.”

4) Discharge (Discharging): “This is the operation of a cell when current

flows spontaneously from the battery into the external circuit.”

5) Anode: It is the negative electrode of a primary cell. It is always

associated with oxidation or the release of electrons into the external circuit.

In a rechargeable cell, the anode acts as negative pole during discharge and

as positive pole during charge.

6) Cathode: It is positive electrode of a primary cell and is always

associated with reduction or taking of electrons from the external circuit. In

a rechargeable cell, the cathode is the positive pole during discharge and the

negative pole during charge.

142

7) Electrochemical Couple: It is the combination of the electrode reactions

of the anode and cathode to form the complete galvanic cell. The number of

electrons given up by the anode to the external circuit must be identical with

the number of electrons withdrawn from he external circuit by the cathode.

8) Impedance or Internal resistance: The impedance or internal resistance

of the battery is the resistance to the flow of current, which operates in

addition to the resistance of the external load.

9) Open Circuit voltage: This is the voltage measured across the terminals

of the cell or battery when no external current is flowing. When measured

on a single cell, it is usually close to the thermodynamic electro-motive force

10) Separator: It is a physical barrier between the positive and negative

electrodes to prevent direct shorting of the electrodes. Separators must be

permeable to ions, but must not conduct electrons. They must be inert in the

total environment.

11) Electrolyte:

“A substance which in aqueous solution or in molten (or fused) state

liberates ions and allows electric current to pass through it, resulting in its

chemical decomposition is called as electrolyte. e.g. acids, bases and

electrovalent salt.”

Q. Define electrolytic cell and electrochemical cell.

Ans: Electrolytic cell: “It is the device in which electrical energy is converted

into chemical energy.” These cells are also known as voltameters. Due to

passage of electric current non spontaneous chemical reaction take place.

Electrochemical cell: “It is the device in which chemical energy is

converted into electrical energy.” In this type of cell the electricity can be

generated by “spontaneous redox reaction”.

143

Q. Differentiate between Metallic conduction (conduction through solid)

and Electrolytic conduction (conduction through liquid)

Ans:Metallic conduction Electrolytic conduction

It involves flow of electrons in a

conductor

It involves movement of ions in a

solution

There is no change in the chemical

properties of conductor.

The chemical reactions take place at the

electrodes with the decomposition of

the electrolyte.

It does not involves any transfer of

matter

It involves transfer of electrolyte in the

form of ions.

It shows the increase in resistance as

the temperature is increased

It shows the decrease in resistance as

the temperature is increased

Q. Give the classification of batteries. OR How batteries are classified?

Ans: Batteries are classified into

1. Primary battery:“The type of battery in which cell reaction is not

reversible is called as primary battery.” These are not rechargeable. If

these are discharged then discarded. e.g. Dry cell, Daniel cell

2. Secondary battery: “The type of battery in which cell reaction is

reversible is called as secondary battery.” These are rechargeable. e.g.

Lead acid storage cell, Ni- Cd-cell.

3. Reserve battery: “It is a battery in which active material are kept

separated by special arrangements.” Such a battery is designed for long

storage before use. e.g. Gordon-magnesium battery, Silver chloride

cell.

144

Q. Write advantages, disadvantages and applications of primary batteries

Ans : Advantages :

Inexpensive

Convenient

Light weight

Good shelf life

High energy density at low/moderate discharges

Disadvantages:

Can only be used once

Leads to large amount of waste batteries to be recycled

Batteries put into landfill sites have severe environmental impact

Life cycle energy efficiency < 2%

Applications:

Portable devices

Lighting

Toys

Memory back-up

Watches/clocks

Hearing aids

Radios

Medical implants

Defense related systems such as missiles

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Q. Write advantages, disadvantages and applications of secondary

batteries

Ans : Advantages:

High power density

High discharge rate

Good low temperature performance

Disadvantages:

Lower energy density

Poorer charge retention

Safety issues

Lack standards

High initial costs

Applications:

Car battery used to start engine

Aircraft systems

Standby power resources

Emergency no fail systems

Electric vehicles

Mobile phones

Power tools

Toys portable computers

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Q. Differentiate between Primary cell and Secondary cell OR How

electrochemical cells are classified?

Ans: Electrochemical cells are classified into primary cell and secondary cell

Primary Cell Secondary Cell

The type of cell in which net cell

reactions cannot be reversed on

applying higher e.m.f. is called as

primary cell

The type of cell in which net cell

reactions can be reversed on applying

higher e.m.f. is called as secondary

cell

Its cost is low Its cost is high

It is light in weight It is heavier

It‟s life is short Its life is longer

It cannot recharge once discharged

E.g. Dry cell, Daniel cell.

It can be recharged number of times.

E.g. Lead acid storage cell, Ni- Cd cell

Q. State Ohms law with mathematical equation and meaning of each

symbol used in it

Ans: Statement:

The strength of current flowing through a conductor is directly proportional

to the potential difference applied across the conductor and inversely

proportional to the resistance of the conductor.

i.e. I = E / R

Where, I = current

E = potential difference

R = Resistance

147

Q. State the types of conductance (conductivity)

Ans : Specific conductivity , equivalent conductivity, Molar Conductivity are the

types of conductance

Q. Define Specific conductivity and equivalent conductivity. State their

units. State the relation between equivalent conductivity and specific

conductivity

Ans: Specific conductivity (conductance) is the reciprocal of specific resistance.

OR It is also defined as the conductance of 1cm cube of solution

It is denoted by (K) kappa.

The unit is ohm-1

cm-1

Equivalent conductivity (conductance) is defined as the conductivity of a

solution containing 1gm equivalent of the electrolyte”

It is denoted by „λ‘

The unit is ohm-1

cm2 eqvt

-1

λ = KV

Where, V is volume of solution containing 1gm equivalent of an electrolyte.

But V = 100/ C

Where, C is concentration in gram equivalent/ litre

λ = K × 1000

C

This is the relation between equivalent conductivity and specific

conductivity

148

Q. Define Molar Conductivity (λm) :

Ans : Molar conductivity of a solution is defined as the conductance of all the ions

present in one mole of electrolyte in the solution

If M is the molar concentration in moles/litre

𝜆𝑚 =1000

𝑀× 𝑘

Units : Molar conductivity is measured in ohm-1

cm2mol

-1

Q. Define conductance. Explain the method of determination

(Measurement) of Conductance in laboratory

Ans : Conductance : The reciprocal of resistance is called as conductance

Unit : ohm-1

or mhos

Procedure:

1. A solution whose conductance to be determined is taken in the

conductivity cell. Since the conductivity varies with temperature, it is

necessary to keep temperature of solution constant. The copper wires of

the circuit dip in mercury placed in glass tubes to complete the circuit.

2. Conductivity cell is connected to a resistance box R on one side and to a

long thin wire AB stretched along a scale of Wheatstone bridge on the

other side.

149

3. Some known resistance „R‟ is taken out of the resistance box. An

alternating current of about 1000-4000 cycles per second is passed

through solution with the help of an induction coil. The sliding contact

„d‟ is moved on the wire AB so that no sound (or minimum sound) is

heard in the head phone. It gives the null point

𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 𝑖𝑛 𝑐𝑒𝑙𝑙(𝑋)

𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑜𝑓 𝑟𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑏𝑜𝑥 (𝑅)=

𝑎

𝑏

∴ 𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 𝑖𝑛 𝑐𝑒𝑙𝑙 𝑋 = 𝑅𝑎

𝑏

∴ 𝑐𝑜𝑛𝑑𝑢𝑐𝑡𝑖𝑣𝑖𝑡𝑦 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 𝑖𝑛 𝑐𝑒𝑙𝑙 =1

𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 𝑖𝑛 𝑐𝑒𝑙𝑙 (𝑋)

= Observed conductance

Where „a‟ and „b‟ are the lengths of wire between movable contact and the

ends of the bridge wire

Q. Define cell constant. How Cell constant is determined?

Ans : Cell constant: The ratio of distance between two electrodes and area of

electrode is called as cell constant

∴ 𝑐𝑒𝑙𝑙 𝑐𝑜𝑛𝑠𝑡𝑛𝑎𝑡 =𝑠𝑝𝑒𝑐𝑖𝑓𝑖𝑐 𝑐𝑜𝑛𝑑𝑢𝑐𝑡𝑎𝑛𝑐𝑒

𝑜𝑏𝑠𝑒𝑟𝑣𝑒𝑑 𝑐𝑜𝑛𝑑𝑢𝑐𝑡𝑎𝑛𝑐𝑒=

0.002765

𝑜𝑏𝑠𝑒𝑟𝑣𝑒𝑑 𝑐𝑜𝑛𝑑𝑢𝑐𝑡𝑎𝑛𝑐𝑒

𝑇𝑕𝑒 𝑢𝑛𝑖𝑡 𝑐𝑒𝑙𝑙 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡 𝑖𝑠 𝑐𝑚−1

Determination of cell constant

Cell constant (1/A) can be determined by measuring the distance between

the two electrodes (l) and their surface aea (A) but, electrodes of

ordinary cell are not exactly 1cm apart and may not possess the surface

area of 1cm2.

150

Therefore, the reciprocal of resistance of cell does not give exact value of

specific conductivity but its value is proportional to it

Therefore the cell constant is determined by substituting the value of

specific conductance of standard N/50 KCl solution at given temperature

250C which accurately determined by Kohlrausch (0.002765).

As we know that , 𝑅 =1

𝑘.𝑙

𝐴

𝑠𝑝𝑒𝑐𝑖𝑓𝑖𝑐 𝑐𝑜𝑛𝑑𝑢𝑐𝑡𝑎𝑛𝑐𝑒 = 𝑘 =1

𝑅

𝑙

𝐴

𝑘 =1

𝑅. x

∴ 𝑋 = 𝑘𝑅 =𝑙

𝐴

𝐹𝑟𝑜𝑚 𝑒𝑞𝑢𝑎𝑡𝑖𝑜𝑛 1 𝑠𝑝𝑒𝑐𝑖𝑓𝑖𝑐 𝑐𝑜𝑛𝑑𝑢𝑐𝑡𝑎𝑛𝑐𝑒 = 𝑜𝑏𝑠𝑒𝑟𝑣𝑒𝑑 𝑐𝑜𝑛𝑑𝑢𝑐𝑡𝑎𝑛𝑐𝑒 x 𝑙

𝐴

= observed conductance x X

= observed conductance x cell constnat

Q. Explain variation of Specific conductance, equivalent conductance,

molar conductance with dilution

Ans : Specific conductivity (k) depends upon

1. The number of ions in the solution

2. The amount of water (solvent) present in soltion. Therefore, as the

dilution increases (amount of water in electrolyte increases) the

conducting power of 1 cm3 of the electrolytic solution decreases. In fact

there are lesser number of ions and more water molecules present in 1

cm3 of solution.

Variation of Equivalent Conductance with dilution

As the degree of dissociation of an electrolytic solution increases with

increase in dilution. Therefore the conducting power of an electrolyte is

due to the ions formed in it, increases with increasing dilution.

151

In other words, the equivalent (or molar) conductivity increases as the

number of ions present in a solution containinng 1 equivalent (or 1

mole) of electrolyte increases with dilution.

Molar conductance increases with increase in dilution

Q. State Kohlrausch‘s law .Give applications of Kohlrausch‘s law

Ans : Statement : The equivalent conductance of an electrolyte at infinite dilution

is equal to the sum of the equivalent conductance of the component ions

The law can be expressed mathematically as

Λ𝜶 = λ a + λ c

Where Λ𝜶 = equivalnet conductivity of electrocyte at infinite dilution

λa = equivalent conductance of anion

λc = equivalent conductance of cation

Application of Kohlrausch law

1. Determination of equivalent conductivity of weak electrolyte

Kohlrausch law has provided a method for determining the Λ0 for weak

electrolyte from λ0 measurements of strong electrolyte. Suppose we want to

calculate Λ0 value for acetic acid, then its value is obtained from λ0 values of

HCl, NaCl and CH3COONa.

According to Kohlrausch law

𝜆0𝐶𝐻3𝐶𝑂𝑂− + 𝜆0𝐻+ = 𝜆0𝐶𝑙

− + 𝜆0𝐶𝐻3𝐶𝑂𝑂− + 𝜆0𝑁𝑎+ − 𝜆0𝑁𝑎+ + 𝜆0𝐶𝑙−

i.e. Λ0CH3COOH = Λ0HCl + Λ0CH3COONa – Λ0NaCl

152

2. Determination of equivalent conductance for sparingly soluble salt

(AgCl) :

The equivalent conductance of sparingly soluble salt (AgCl) also can be

obtained by the similar method.

Λ0AgCl = Λ0NH4Cl + Λ0AgNO3 – Λ0NH4NO3

3. Determination of the solubility of sparingly soluble salt :

The solubility of the sparingly soluble salts like Gal, BaSO4 can calculate

by using the following relation

Λ0 =1000k

S

S = Solubility in gm eq lit

K is determined by using Wheatstone bridge, Λ0 is calculated using

Kohlrausch‟s law,

Λ0(salt) = Λ0+ + Λ0

-

4. Determination of degree of dissociation

Degree of dissociation (𝛼 ) is the fraction of the molecules ionized into ions

𝛼 =𝑁𝑜. 𝑜𝑓 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑎𝑟 𝑖𝑜𝑛𝑖𝑧𝑒𝑑 𝑖𝑛𝑡𝑜 𝑖𝑜𝑛𝑠

𝑡𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒𝑠 𝑡𝑎𝑘𝑒𝑛

This equation may be written as

Λ = 𝜶 = 𝑵𝒐.𝒐𝒇 𝒎𝒐𝒍𝒆𝒄𝒖𝒍𝒆𝒔 𝒊𝒐𝒏𝒊𝒛𝒆𝒅 𝒊𝒏𝒕𝒐 𝒊𝒐𝒏𝒔 𝒂𝒕 𝒂 𝒑𝒂𝒓𝒕𝒊𝒄𝒖𝒍𝒂𝒓 𝒅𝒊𝒍𝒖𝒕𝒊𝒐𝒏

𝒕𝒐𝒕𝒂𝒍 𝒏𝒐.𝒐𝒇 𝒎𝒐𝒍𝒆𝒄𝒖𝒍𝒆𝒔 𝒕𝒂𝒌𝒆𝒏

Λ, can be obtained from conductivity measurements, Λ0 can calculated using

Kohlrausch law

153

Q. Explain construction and working of Lead acid storage cell (Lead

accumulator). Write charging and discharging reactions.

Ans: It is secondary cell it is reversible cell and can be charged.

Construction:

1. Lead acid storage cell consist of lead plate which acts as anode and lead

plate coated with lead oxide (PbO2) which acts as cathode.

2. Several such an anode and cathode pairs are connected in parallel and are

dipped in 20% of H2SO4 solution with specific gravity 1.25g/cm3.

3. The battery is encased in plastic or glass container.

4. Each pairs of anode and cathode produces a voltage of 2 Volt.

Working:

Due to the formation of water in the cell the acid get diluted. When its

specific gravity falls below 1.25gm/cm3 the battery needs charging.

154

The following discharging and charging reactions take place.

Discharging

At anode: Pb + SO4--

PbSO4 + 2e-

Charging

Discharging

At cathode: PbO2 + SO4--

+ 4H++2e

- PbSO4 + 2H2O

Charging

_________________________________________________________

Net cell reaction:

Discharging

Pb +PbO2 + 4H++2SO4

-- 2PbSO4 + 2H2O

Charging

During charging lead & lead oxide is again deposited on anode & cathode

respectively & charging reaction is

Discharging

2PbSO4 + 2H2O Pb + PbO2 + 2H2SO4

Charging

Applications:

1. Lead acid battery used in starting motor and power station

2. It is used in UPS system & research centers

3. It is used in marketing area, railway signaling in mines, laboratories and

hospitals

4. It is used in security alarms system, cars, buses and trucks.

Advantages

1. It is made easily

2. It reduces very high current.

3. The self discharging rate is low

4. It work, effectively even at two temperature.

155

Q. What is fuel cell? Explain construction & working of Hydrogen-Oxygen

(H2O2) fuel cell. Write applications of H2O2 fuel cell.

Ans: Fuel cell: “A fuel cell is an electrochemical cell which can convert the

chemical energy of fuel directly into electrical energy by an electrochemical

process, in which the fuel is oxidized at the anode.”

Construction:

1. It consists of two inert porous graphite electrodes coated with an electro

catalyst such as finely divided Pt- Co –Ru.

2. Aqueous KOH or NaOH is used as electrolyte.

3. A wick is placed to maintain water balance.

Working:

1. Hydrogen gas and oxygen gas are continuously supplied to anode and

cathode respectively under a pressure of about 50 atmospheres.

2. Then the hydrogen undergoes combustion generating electric current.

The emf of cell is 1.23 V

156

The following electrode reactions take place

At anode:

2H2(g) 4H+

+ 4e-

At cathode:

O2 + 4e- 2O

--

Net cell reaction: 2H2 + O2 2H2O

Applications:

It is used in space vehicles, space aircrafts, mobile power system and

submarine military vehicles.

Q. Write the advantages & limitation of Hydrogen-Oxygen fuel cell (Fuel

cell)

Ans: Advantages:

1. There is no emission of gases & pollutant

2. It required low maintenance cost.

3. It can be operated at room temperature

4. It saves fossil fuels

5. There is low noise pollution by using this cell

6. Its efficiency is very high

7. Modular and hence parts are exchangeable

Limitations (Disadvantages):

1. It require high initial cost

2. It require large weight & volume for gas-storage system

157

3. It require high cost of pure hydrogen

4. There is lack of infrastructure for distributing hydrogen

5. The life spans of the cell is not accurately known

Q. Explain the construction and working of Nickel – metal hydride battery

Ans : Construction: Nickel Metal hydride battery is made up of anode

containing metal hydride such as ZrH2, VH2 and TiH2 with hydrogen storage

metal alloy such as La Ni5 or TiNi. Cathodes consisting of nickel oxy

hydroxide both the compartments are separated by polypropylene. KOH

used as electrolyte.

Working: Then cell reactions are as follows

At anode: MH + OH-

M + H2O + e-

At cathode: NiO [OH] + e- + H2O Ni (OH)2 + OH

-

NCR : MH + NiO (OH) M + Ni (OH)2

Applications: Used in electric vehicles, laptops, and cellular phones and

designed for electrically run automobiles.

158

Advantages:

Resistance to chemical oxidation

High energy storage capacity

Long cycle life and shelf life

No maintaince required

Q. What are Lithium cells? Explain the construction and working of

Lithium MnO2 battery? Mention the advantages

Ans : Lithium cells

Lithium cells are most popularly used cells, which are available in various

configurations such as button type, bobbin type, spiral wound prescematic,

rectangle etc configuration.

Construction:

Lithium manganese dioxide cell consisting of anode containing lithium and

the cathode can containing of specially heat-treated manganese dioxide

(MnO2). Both anode and cathode are separated by a separator made up of

polypropylene impregnated with the electrolyte. (Metal salt such as LiCl,

LiBr, LiAlCl4 which are mixed in a organic solvent such as 1,2 dimethoxy

ethane, and propylene carbonate).

The cell delivers an emf of 3V.

159

Working: The cell reactions are as follows

At anode: Li Li+ + e

-

At cathode: Li+ + MnO2 + e

- [Li] MnO2

NCR : Li + MnO2

[Li] MnO2

During the all reactions Mn IV stage reduced to Mn III stage.

Uses: Li – MnO2 cells are used in Safety and Security Devices, Calculator,

watches, automatic camera, memory batteries, cellular phones etc.

Advantages:

These are light in weight

High energy density

More cycle life

Q. Explain the construction and working of Methanol – Oxygen fuel cell

Ans : Construction: It consist of two electrodes made up of platinum in between

the electrodes H2SO4 is placed as a electrolyte. Methanol and H2SO4 is

placed as a electrolyte.

160

Working: Methanol and H2SO4 is supplied at the anode and pure oxygen

gas is supplied at the cathode. The methanol is oxidized to CO2 and H2O

with the liberation of electrical energy. The cell delivers an emf of 1.20 V.

The cell reactions are as follows

At anode : CH3OH + H2O CO2 + 6H

+ + 6e

-

At cathode : 3/2 O2 + 6H + + 6e

-

3H2O

NCR : CH3OH + 3/2 O2 CO2 + 2H2O

Application:

1. It is used in space craft continues power supply.

2. It is used in military for large scale power production.

Q. Explain the Classification of fuel cells based on the electrolyte

Ans : Fuel cells are classified into the following types based on the type of

electrolyte used

1. Alkaline fuel cells

2. Phosphoric acid fuel cell.

3. Molten carbonate fuel cell.

4. Solid oxide fuel cell

5. Solid polymer electrolyte fuel cell.

1. Alkaline fuel cells: These fuel cells containing alkali such as KOH or

NaOH as electrolyte. Hydrogen is used as fuel and oxygen gas is used as

an oxidant. The cell operates at a temp of 800C.

Uses: These are used in emergency lights and portable power

generations, space applications, military applications etc.,

2. Phosphoric acid fuel cells: These fuels cells consisting of 98%

phosphoric acid, 2% water as electrolyte, O2 is used as oxidant

161

Hydrogen LPG, NPG etc are used as fuels. These operate at a temp 190

to 2000C. Platinum alloys such as platinum cobalt chromium, are used as

electro catalyst.

Uses: These cells are used to provide light and heat in large buildings

3. Molten carbonate fuel cells: These fuel cells consisting of molten

carbonates such as lithium carbonate 26.2% and potassium carbonate

(K2CO3) 23% and lithium. Aluminium carbonate as electrolyte. The

anode is made up of nickel and cathode made up of nickel oxide.

Operating temperature is 6500C.

Uses: These are used in chemical industries such as aluminium

chloroalkali industries

4. Solid oxide fuel cells: These contains ZrO2, Y2O3 are solid electrolytes.

Cathode is made up of porous strontium doped with LaMnO3 or In2O3

and SnO2. Anode is made up of cobalt, nickel, or ZrO2. Operating

temperature is 10000C.

Uses : These cells are used in KW power plants, water heating etc.

5. Solid polymer Electrolyte: These contain ion exchange membrane as

solid electrolyte for ionic conduction “nafion – R” membranes which are

chemically and electrochemically stable at 2000C are used. Operating

temperature of the cell is 800C. The electrodes are made up of platinum

and noble metals are used as electro catalysts.

Uses: Used in the manned Gemini terrestrial orbital missions

Q. Give the classifications of Fuel cells based on temperature

Ans : Fuel cells are the galvanic cells in which chemical energy of fuel is directly

converted into electrical energy

162

Classification of Fuel cells

These are classified into three types as follows

1. Low temp fuel cells: This operates at the temp range about 750C and

contains water base electrolytes.

2. Moderate temp fuel cells: Which operates at the temp range about

6000C and contains salt electrolyte

3. High temp fuel cells: This operates at the temp range about 10000C and

contains ceramics as electrolyte.

Q. Give applications of fuel cells

Ans: Application of fuel cells

Alkaline fuel cells: These are used in emergency lights and portable power

generations, space applications, military applications etc.,

Phosphoric acid fuel cells: These cells are used to provide light and heat in

large buildings

Molten carbonate fuel cells: These are used in chemical industries such as

aluminium chloroalkali industries

Solid oxide fuel cells: These cells are used in KW power plants, water

heating etc.

Solid polymer Electrolyte: Used in the manned Gemini terrestrial orbital

missions

163

References

Engineering Chemistry – Jain and Jain, S. S. Dara, Shashi Chawla,

Industrial Chemistry – B.K. Sharma

Polymer Science – V.R. Gowariker

Instrumental Methods of Chemical Analysis – B.K. Sharma

Environmental Chemistry – B.K. Sharma, A.K. De, S. S. Dara

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Prof. Atul B. Waghmare [9527202189, 9657824223]

[ M. Sc. Analytical Chemistry ]

E-mail – abwaghmare28@gmail.com

Shri Yogeshwari Polytechnic College, Ambejogai

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