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Engineering Chemistry 18CHE12/22

Dept of Chemistry/SVCE

Module – 1

MODULE- I: Electrochemistry and Energy storage systems

Use of free energy in chemical equilibria: Thermodynamic functions: Definitions of free energy and entropy. Cell potential, derivation of Nernst equation for single electrode potential, numerical problems on E, E0, and Ecell. Electrochemical Systems: Reference electrodes: Introduction, construction, working and applications of Calomel electrode. Ion-selective electrode – Definition, construction and principle of Glass electrode, and determination of pH using glass electrode. Electrolyte concentration cells, numerical problems. Energy storage systems: Introduction, classification - primary, secondary and reserve batteries. Construction, working and applications of Ni-MH and Li-ion batteries. (RBT Levels: L3)

ELECTROCHEMISTRY & ENERGY STORAGE SYSTEMS

Introduction:

A part of a total energy of a system is converted in to work and the rest is unavailable. Any kind of work which is converted into useful work is called as available energy. Energy which cannot be converted into useful work is known as unavailable energy which is represented as Entropy function. Isothermally available energy of a system is known as free energy (Gibb‘s Free energy) Entropy, the measure of a system‘s thermal energy per unit temperature that is unavailable for doing useful work.

OR The amount of entropy is also a measure of the molecular disorder, or randomness, of a system. (Because work is obtained from ordered molecular motion)

dS=dQ/T

dS= Change in entropy, dQ=change in energy & T is the temperature.

∆S= 0 for reversible process

∆S>0 for irreversible process

Entropy change depends on system and surrounding. To study the above system a new thermodynamic function is introduced- which is free energy. Free energy is a point function.

https://www.britannica.com/science/energy

https://www.britannica.com/science/energy

https://www.britannica.com/science/temperature

https://www.britannica.com/science/work-physics

https://www.merriam-webster.com/dictionary/entropy

https://www.britannica.com/science/molecule

https://www.britannica.com/science/motion-mechanics



Free energy is a composite function that balances the influence of energy vs. entropy.

The Gibbs free energy G: G = H – TS ------------------1

Where G= Gibbs free energy, H= Enthalpy, T= Constant Temp, S= Entropy

Consider a change A B

GA, HA, and SA are Gibb‘s free energy, Enthalpy and Entropy of reactant A respectively.

GB, HB, and SB are Gibb‘s free energy, Enthalpy and Entropy of product B respectively.

Calculation of change in free energy during a chemical change is given as follows:

∆G= GB-GA = (HB-HA) – T(SB-SA)

∆G=∆H-T∆S

Above change continue till equilibrium is attained. At equilibrium, the second Law states that

dQ= TdS

Under Constant temperature and pressure dH= TdS

For a finite change ∆H=T∆S

At Equilibrium ∆G=∆H-T∆S=0

Significance of Free Energy

∆G= 0 Reaction at equilibrium

∆G= -ve spontaneous reaction

∆G= +ve non-spontaneous reaction

∆G= -nEF for work done in a redox reaction at a given temp

∆G˚= -nE˚F for work done in a redox reaction at 298˚ K



ELECTROCHEMISTRY

On passing electric current through an electrolytic solution causes chemical reaction to take

place. The reverse is also true i.e,.generation of electric current takes place by chemical reaction.

Depending up on these two types of electrochemical processes there are two types of cells such

as

1) Electrolytic cell: is the cell that converts electrical energy into chemical energy.

2) Galvanic cell or Electrochemical Cell: is the cell that converts chemical energy into electrical

energy.

Red-ox (Reduction-Oxidation) reactions are the basis for electrochemical cells. An

electrochemical cell consists of two electrodes; each electrode is referred as ‘Half Cell’ or

‘Single Electrode’ connected by a metallic wire and electric current flows of as a result

spontaneous red-ox reaction.

Difference between an electrolytic cell and a galvanic cell

Electrochemical cell or Galvanic Cell Electrolytic cell

A Galvanic cell converts chemical energy into

electrical energy.

An electrolytic cell converts electrical

energy into chemical energy.

The redox reaction is spontaneous and is

responsible for the production of electrical energy.

The redox reaction is non spontaneous and

electrical energy has to be supplied to initiate

the reaction.

The two half-cells are set up in different containers

being connected through the salt bridge or porous

partition.

Both the electrodes are placed in a same

container in the solution of molten

electrolyte.

The anode is negative and cathode is the positive

electrode.

The anode is positive and cathode is the

negative electrode.

The electrons are supplied by the species being

oxidized. They move from anode to the cathode in

the external circuit.

The external battery supplies the electrons.

They enter through the cathode and come out

through the anode.

The electrodes are of different metal. The electrodes may be of same metal or

different metal.

ELECTROCHEMICAL CONVENSIONS 1.Representation of Electrode:

It oxidation reaction takes place at anode,then the electrode is represented as M/Mn+

It reduction reaction takes place at the cathode then the electrode is represented as Mn+

/M The vertical lines indicated the contact between metal electrodes and metalions.



2.Representation of Cell:

The following points have to be noted to represent an electrochemical cell

a>Anode is always written to LHS.

b>Cathode of the cell is written to RHS of the anode.

c>The two vertical lines denotes the salt bridge and interface between the two electrodes.

Cell notation is given by M / Mn+

// Mn+

/ M

Ex.Zn(s) / Zn+2

//Cu+2

/Cu(s) 3.Calculation of emf of the cell:

According to electro chemical application

Ecell = Ecathode – Eanode.

If the EMF value is + ve then the reaction is spontaneous & if It is –ve the reaction is

nonspontaeous.

SINGLE ELECTRODE POTENTIAL(E)

Single electrode potential is defined as the potential developed at the interface between the metal and electrolytic solution,when it is contact with solution of its own ions.

STANDARD ELECTRODE POTENTIAL(E0)

It is the potential measured, when the electrode is in contact with solution of unit concentration

at 298K.If the electrode involves gas,then gas is at1atmpressure.

EMF OF THECELL(Ecell)

The potential difference between the two electrodes of the galvanic cell which causes the flow

of current from one electrode (higher potential) to the other (lower potential) is know as EMF

of the cell.

EMF = E0

Cathode - E0

Anode

‘



Nernst Equation:

Nernst derived a equation to establish relationship between electrode potential and concentration

of metal ion.

The decrease in free energy represents maximum amount of work.

i.e. –Δg = Wmax (1)

Wmax for an electrochemical cell is given by the equation

Wmax = nFE (2)

On comparing eqn (1) & (2) we have

-ΔG = nFE OR ΔG = -nFE

Under standard conditions the free energy ΔG is given by the equation

ΔG° = -nFE°

E° is a constant called standard reduction potential.

Consider a reduction reaction:

Mn+ + ne- M

For spontaneous reaction, the change in the free energy depends on the concentration of reacting

species.

ΔG = ΔG° + RT lnKc (3)

Where Kc = [Products]

[Reactants]

Substituting for Kc in (3) we get

ΔG = ΔG° + RT ln [Product]

[Reactant]

ΔG = ΔG° + RT ln [M] (4)

[Mn+]

Substitute for ΔG and ΔG° in eqn (4)

-nFE = -nFE° + RT ln [M] – ln [Mn+]

Under standard conditions [M] = 1

Hence, -nFE = -nFE° – ln [Mn+] (5)

Dividing eq-(5) by –nF we get

E = E° + RTln [Mn+]

nF



Converting ln to log we get

E = E° + 2.303RT log [Mn+] (6)

nF

Substituting for RT and F in eqn (6) we get

E = E° + 0.05918 log [Mn+] (7) (For reduction reaction)

n

E = E° - 0.05918 log [Mn+] (7) (For oxidation reaction)

n

Nernst equation can also be applied for the calculation of emf of a chemical cell by using the

following equations:

1) E = E° + 0.05918 log [species at cathode]

n [species at anode]

2) E = E° + 0.05918 log [Product]

n [Reactant]

Reference electrode:

Reference electrode is the electrodes whose potentials are known and are used for

determination of potentials of other electrodes.

Types of reference electrodes:

1) Primary reference electrode

2) Secondary reference electrode

Primary reference electrode: Standard hydrogen electrode (SHE) is used as primary electrode.

SHE – whose potential is arbitrarily taken as zero at all temperatures.

Limitations of SHE:

1) Difficulty in setting up of the electrode

2) It is difficult to maintain the pressure of hydrogen gas at 1atm uniformly.

3) It is difficult to maintain one atm pressure of H2 gas uniformly for a long time.

4) Platinum foil gets poisoned easily by the adsorption of impurity in the solution.

5) The equilibrium between H+ ions and hydrogen gas gets disturbed due to adsorption of

impurities.

6) The hydrogen electrode cannot be used in the presence of oxidizing agents. (As H2 gas a

reducing agent and it reacts with oxidizing agent)

Secondary reference electrode: Whose potential with respect to SHE are known. Secondary

reference electrodes have several advantages over SHE. These electrodes are commonly used for

determining the electrode potentials.

The two commonly used secondary reference electrodes are calomel electrode and silver-

silver electrode.



KCl solution

Hg2Cl2 Hg

Pt

Calomel Electrode:

It is very convenient secondary reference electrode. The Calomel

electrode consists of solid mercury in contact with a sparingly soluble

Hg2Cl2 and dipped in KCl solution.

Calomel electrode consists of solid mercury placed at the bottom of the

tube, which is covered with the paste of calomel (Hg2Cl2), over which the

potassium chloride solution is introduced. A platinum wire dipped into

the mercury gives external electrical contact. The electrode is represented

as: Cl- / Hg2Cl2 /Hg

The potential of a calomel electrode depends on the concentration of KCl used.

The Potential developed for:

- 0.1 M KCl solution is +0.334 V.

- 1 M KCl solution it is +0.281 V

- Saturated KCL solution it is +0.242 V

Calomel electrode behaves as anode or cathode depending upon the nature of other electrode.

The net cell reaction when it acts as an anode is

When it acts as anode, the electrode reaction is,

2Hg Hg22+

+ 2e-

Hg22+

+ 2Cl-

Hg2Cl2

2Hg + 2Cl-

Hg2Cl2 + 2e-

When it acts as cathode, the electrode reaction is,

Hg22+

+ 2e- 2Hg

Hg2Cl2 Hg22+

+ 2Cl-

Hg2Cl2 + 2e- 2Hg + 2Cl

-

The net cell reversible electrode reaction is,

The net cell reaction when it acts as a cathode is

Hg2Cl2(s) + 2e-2Hg(l) + 2Cl-

The Nernst equation is given by,



Uses: is used as a secondary reference electrode in the measurement of single electrode potential.

Advantages:

1) Easy to constructed

2) Highly reproducible

3) Stable for long period

4) Temperature invariant

Applications:

1.It is used as secondary reference electrode in the measurement of single electrode. 2. It is used as reference electrode in all potentiometer determinations 3. It is used as a secondary reference electrode in place of calomel electrode / glass electrode / ion selective electrodes. 4. Used in determining whether the potential distribution is uniform or not in ship hulls and old pipelines protected by cathodic protection.

5. As a portable reference electrode for measuring the different depths of oil rigs anplatforms, submerged oil pipelines etc. usually such probe is powered by Ni – Cd battery and can operate up to a depth of 300-400m with precision of ±1mv.

Ion-selective electrodes:

The electrode, which responds to a specific ion in a mixture by ignoring other ion, known

as ion selective electrode. It consists of a thin membrane in contact with ion solution. It has the

ability to respond to a specific ion and develop a potential on membrane. In ion selective

electrode, the membrane will be in contact with an analyte solution on one side and internal

reference solution on the other side and internal reference electrode dipped in internal reference

solution, schematically represented as

Membrane

Solution to be Internal Internal

analysed (C1) Standard Solution (C2) Reference Electrode

The potential developed across the membrane is due to the difference in concentration of analyte

solution and internal standard solution. By convention

Ecell= RT log C2 - RT log C1

nF nF

Ecell= RT log C2

nF C1

Uses:

1)used in the determination of cations such as H+, Li+, K+, etc and anions such as CN-, NO3-, F-,

etc.

2) used in determination of pH by using H+ ion selective electrode.

3) Used to determine the concentration of gas in presence of gas-sensing electrode.



Glass Electrode:

Ag-AgCl electrode

Ag/AgCl

0.1 M HCl [H+]=C2

H+ ion [H+]=C1

Cell representation: Ag / AgCl / HCl (0.1M) / Glass.

Glass membrane selectively responses to hydrogen ions.

This electrode works on the principle that when a thin and low resistivity glass membrane is in

contact with a solution containing H+ ions, a potential develops between the membrane and the

solution. Potential developed depends on the concentration of hydrogen ions in the solution.

When the concentration of hydrogen ions is different on either side of the glass membrane, the

potential develops across the membrane.

Construction:

A long glass tube with a thin walled glass bulb (sense H+ ions up to pH-9) contains 0.1 M HCl.

An Ag/AgCl electrode placed in the solution connected by a platinum wire for electrical contact.

The electrode containing H+ ions of concentration C1 is dipped in another solution of

concentration C2. A change in H+ ion concentration causes a change in the composition of glass,

due to exchange of ions by inner membrane and outer membrane resulting in a boundary

potential Eb.

At Equilibrium, Na+(glass) + H+

(aq)⇔ Na+(aq) + H+

(glass)

Membrane

Solution to be Internal Internal

Analyzed (C2) Standard Solution (C1) Reference Electrode

(H+ ions) (0.1 M HCl) (Ag/AgCl electrode)

E1 E2

Eb= E1-E2 (E1& E2 is the potential developed at outer and inner membrane respectively)

Where E1= 0.0591/n logC2 and E2= 0.0591/n logC1

Then boundary potential

Eb= E1-E2= 0.0591logC2 - 0.0591logC1 (n= [H+] =1)



C1 is constant due to known electrolyte taken in bulb,

Then -0.0591logC1=constant=L

C2 = [H+] ions in outer membrane then,

Eb= L+ 0.0591 log [H+]

Eb= L - 0.0591 pH (pH = -log[H+])

Advantages: Disadvantages:

1) It is used in both oxidizing and reducing

agents.

2) It is simple to operate.

3) It provides accurate results.

4) It is not poisoned easily.

5) It is used to determine the pH of a solution

in the range 0-10

1) Cannot be used for acids having pH < 1.

2) Cannot be used in the presence of fluoride

ions.

3) Cannot be used in alcohol and some organic

solvents.

Determination of pH of a Solution using Glass Electrode:

The potential of a glass electrode depends on the concentration of H+ ions. Hence, pH of

a solution can be determined by using glass electrode and calomel electrode assembly. The cell

assembly is represented as

Cl-/Hg2Cl2/Cl- // solution of unknown PH / glass/0.1 M HCl / AgCl / Ag

The emf of a cell is determined by using high impedance voltmeter.

Ecell is the difference b/w glass electrode potential EG and the calomel electrode potential ESCE

Ecell = EG - ESCE = L1 – 0.0591pH – ESCE

PH = L1 - ESCE - Ecell

0.0591

L1 – a constant K can replace ESCE

PH = K - ESCE

0.0591

In order to evaluate K, a solution of known pH is used and the potential of the cell is measured

Electrolyte Concentration cells:

“Electrolyte Concentration cell is an electrochemical cell in which the electrode material and the

solution in both the electrodes are composed of the same substances but only the concentrations

of the two solutions (electrolyte) are different”.

A typical example of Copper concentration cell is shown below.



Concentration Cells:

When two electrodes of a same material are introduced into a solution of same

electrolyte, having same concentration the potential developed is 0. Hence, current does not flow

through the circuit. When electrodes of same material are dipped in a solution of different

concentrations, the potential is developed. Such cells are called concentration cells.

Construction of a cell in which the emf is produced by difference in concentration of

solution.

Consider a cell in which both the electrodes are made up of copper metal dipped in

CuSO4 solution of different concentration.

Cell Notation: Cu | Cu2+ (M1) || Cu2+ (M2) | Cu

Where M1 and M2 are the molar concentration of the Cu2+ in the two, half cells. The copper

electrode, which is in contact with a solution of higher concentration acts as cathode and that

with lower concentration, acts as anode.

The half-cell reactions are:

Cu Cu2+ (M1) + 2e (anode)

Cu2+ (M2) + 2e Cu (cathode)

The net cell reaction is:

Cu2+ (M2) Cu2+ (M1)

The current flow is due to change in concentration. This takes place until the concentration in the

two half-cells become equal.

Ecell = ER - EL (R – Right & L – Left)

=

E° + 0.0591 log M2 E° + 0.0591 log M1

n n

Ecell= 0.0591 log M2

n M1

Cu Cathode

SaltBridge

[Cu2+] = M2

Cu Anode

[Cu2+] = M1

V

Voltmeter

- +



ENERGY STORAGE SYSTEMS

Introduction

● A battery is a portable energy source with three basic components-an anode (the negative

part), a cathode (the positive part), and an electrolyte. As current is drawn from the battery,

electrons start to flow from the anode through the electrolyte, to the cathode.

● A device enables the energy liberated in a chemical reaction to be converted directly into

electricity.

● The term battery originally implied a group of cells in a series or parallel arrangement, but

now it is either a single cell or group of cells.

● Examples: It ranges from small button cells used in electric watches to the lead acid batteries

used for starting, lighting and ignition in vehicles with internal combustion engines.

● The batteries are of great importance based on the ability of some electrochemical systems to

store electrical energy supplied by the external source. Such batteries may be used for

emergency power supplies, for driving electric vehicles, etc.

● For the commercial exploitation, it is important that a battery should provide a higher energy,

power density along with long shelf life, low cost and compatible rechargeable units.

Battery: It is a device consisting of two or more galvanic cells connected in series or parallel or

both.

Principle components of a battery are:

1. An anode where oxidation occurs.

2. A cathode where reduction occurs.

3. An electrolyte, which is ionically conducting.

4. A separator to separate anode and cathode compartments.

Classification of batteries:

1. Primary batteries: In these batteries the cell reaction is not reversible after discharging cannot

be rechargeable. e.g. Zn-MnO2 dry cell.

2. Secondary batteries: In this battery the cell reaction is completely reversible after discharging

can easily rechargeable. e.g. Lead-acid battery, Ni-MH battery.

3. Reserve batteries: In these batteries, one of the active components (e.g. electrolyte) of the

battery is separated from the rest of the components. It is assembled just before the use. e.g. Mg-

water activated the battery.



Nickel-metal hydride battery (Ni-MH)

Nickel metal hydride (metal hydride is a binary compound formed by the union of hydrogen and

other elements) batteries are similar to Ni-Cd battery, but are less toxic and offer higher

capacities. Ni-MH batteries have a high self-discharge rate and are relatively expensive to

purchase.

Construction:

● In a Ni-MH cell, a hydrogen storage metal alloy behaves as anode and nickel oxy hydroxide

cathode.

● At cathode (a highly porous substrate) nickel oxy hydroxide is impregnated.

● The electrolyte is an aqueous potassium hydroxide solution.

● Synthetic non-woven material used as a separator that separates the two electrodes and

behaves as a medium for absorbing the electrolyte.

● Electrode reactions are:

At anode: MH + OH-—> M + H2O + e-

At cathode: NiO(OH) + H2O + e- —> Ni(OH)2 + OH-

Over all reaction: NiO(OH) + MH —> Ni(OH)2 + M

● The open circuit voltage is 1.35V.

● During recharging of the battery the above cell reaction is reversed.

● Advantages Disadvantages: Uses:

● Higher capacity

● Long shelf life

● Simple storage and

transportation

● Environmentally friendly

● Limited service life

● Limited discharge

current

● High self-discharge

● High maintenance

● Cellular phones

● Emergency

● Power tools

● Portable electric

vehicles



Lithium-ion battery (Li-ion Battery)

1.Li-ion batteries are secondary batteries.

2.The battery consists of a anode of Lithium, dissolved as ions, into a carbon.

3.The cathode material is made up from Lithium liberating compounds, typically the three

electro-active oxide materials,

Principle

1. During the charge and discharge processes, lithium ions are inserted or extracted from

interstitial space between atomic layers within the active material of the battery.

2. Simply, the Li-ion is transfers between anode and cathode through lithium Electrolyte.

.Since that of a Lithium metal battery

These batteries with high energy density, high energy efficiency, high voltage and long life

cycle. Lithium has the following characteristics.

(i) It is light weight. (ii) It has high electrochemical equivalence (3.86 Ah g-1). (iii) It has good

electrical conductivity. (iv) It has high standard electrode potential (-3.05V).

construction and working: A conventional lithium ion battery consists of and a metal oxide such as carbon (graphite) forms

the anode and lithium cobalt oxide (LiCoO2) as a cathode. The electrolyte consists of a lithium

salt in an organic solvent. The salts include lithium hexafluorophosphate LiPF6, lithium

tetrafluoroborate LiBF4 and lithium perchlorate LiClO4. The solvents used are ethylene

carbonate, dimethyl carbonate, and diethyl carbonate. The cell delivers an emf of 4V.



Advantages

1. They have high energy density than other rechargeable batteries

2. They are less weight

3. They produce high voltage out about 4 V as compared with other batteries.

4. They have improved safety, i.e. more resistance to overcharge.

5. No liquid electrolyte means they are immune from leaking.

6. Fast charge and discharge rate

Disadvantage: 1. They are expensive

2. They are not available in standard cell types.

Applications 1. The Li-ion batteries are used in cameras, calculators.

2. They are used in cardiac pacemakers and other implantable device.

3. They are used in telecommunication equipment, instruments, portable radios and TVs,

pagers. They are used to operate laptop computers and mobile phones and aerospace

application.



Most probable Questions

1. Define single electrode potential. Derive the Nernst equation for single electrode

potential. (L1)

2. Define the following: a) Free energy b) Entropy (L1) 3. What are concentration cells? Explain the construction and working of a copper concentration cell. ( L2) 4. Define reference electrode. Explain the construction and working of Calomel electrode. (L2)

5. What is an ion selective electrode? Construct the Glass electrode and explain the principle and working of Glass electrode. (L3)

6. Explain the construction and working of Glass electrode? (L2)

Illustrate how a glass electrode can be used in the determination of a PH of a

solution. (L3)

7. Explain the determination of electrode potential by using Calomel electrode. (L1)

An electrochemical cell consists of metallic zinc immersed in 0.1 M Zn(NO3)2 solution and metallic copper immersed in 0.2 M CuSO4 solution. Calculate emf of

the cell at 250C and change in free energy of the cell reaction E0cell = 1.1 V. (L3)

8. Emf of the cell Ag/AgNO3(C1) // (C2 = 0.2) AgNO3 /Ag is 0.8 V. Calculate C1 of the cell. (L3) 9. Define Battery? Explain the classification of batteries with suitable example. (L2)

Explain the construction, working and applications of a Ni-Metal hydride

Battery (L2)

10. Discuss the construction and working of a Li-ion battery. (L3)

11. Lithium batteries are more advantageous over other batteries. Explain. (L2)

Note: Refer the Numerical problems which are solved in the class.

Engg.Chemistry

SVCE Page 1

MODULE-II:

Corrosion and Metal finishing Corrosion: Introduction, Electrochemical theory of corrosion, Factors affecting the rate of corrosion: ratio of anodic to cathodic areas, nature of metal, nature of corrosion product, nature of medium – pH, conductivity and temperature. Types of corrosion - Differential metal and Differential aeration - pitting and water line). Corrosion control: Anodizing – Anodizing of aluminium, Cathodic protection - sacrificial anode and impressed current methods, Metal coatings - Galvanization. Metal finishing: Introduction, Technological importance. Electroplating: Introduction, principles governing electroplating-Polarization, decomposition potential and overvoltage. Electroplating of chromium (hard and decorative). Electroless plating: Introduction, electroless plating of nickel & copper, distinction between electroplating and electroless plating processes. (RBT Levels: L1 & L2)

Corrosion and Metal Finishing Definition of corrosion:-

Corrosion can be defined as “The destruction (or) deterioration (or) loss of metals or

alloys by the surrounding environment through chemical (or) electrochemical reactions”.

Ex: - 1. Rusting of Iron: - A reddish brown scale formation on iron objects.

Fe 2+ + 2OH- Fe (OH) 2

4Fe (OH) 2 + O2 + 2H2O [Fe2O3.3H2O]

Hydrated Ferric Oxide [rust]

2. Green scales formed on copper vessels.

Corrosion may occur either in a dry environment (or) in an aqueous medium. The former

is called dry corrosion and the later is called wet corrosion.

Dry corrosion [chemical corrosion]

Dry corrosion involves the direct attack of metals by dry gases mainly through chemical

reactions.

It occurs by direct attacks of atmospheric gasses such as oxygen, hydrogen, sulphide,

halogens and Sulphur-dioxide on the metal forming oxide layer.

Ex: - the attack of dry air (or) oxygen on a metal to form an oxide layer over the surface.

Wet corrosion [Electrochemical corrosion]

Wet corrosion involves reactions in aqueous solution medium. The conducting surface of

the metal undergoes an electrochemical reaction with the moisture and oxygen present in the

atmosphere.

Ex: - Rusting of Iron.

Wet corrosion is explained on the basis of electrochemical theory.

Engg.Chemistry

SVCE Page 2

Electrochemical theory of corrosion:-

Electrochemical Theory taking Iron as example:-

According to electrochemical theory, when a

metal such as iron is exposed to corrosive

environment, following changes occur. A large

number of tiny galvanic cells with anodic and

cathodic regions are formed.

At the anodic region oxidation reaction takes

place and the metal gets converted into its ions,

liberating electrons. Consequently, metal undergoes corrosion at the anodic region.

At the cathodic region, reduction reaction takes place. Since the metal cannot be reduced further,

metal atoms at the cathodic region are unaffected by the cathodic reaction.

At Anode:-

At anode ox ideation takes place in which the metal atoms are converted into their ions liberating

electrons.

Fe Fe2+ + 2e-

At Cathode:-

The cathodic reaction is based on nature of the environment.

a). In the absence of oxygen.[Libration of Hydrogen]

i) In acidic medium, liberation of hydrogen takes place.

2H+ + 2e- H2

ii) In neutral (or) alkaline medium, Hydroxide ions are formed with simultaneous liberation of

hydrogen.

2H2O + 2e- 2OH- + H2

b). In presence of oxygen:- [Absorption of oxygen]

i). In acidic medium, absorption of oxygen takes place.

4H+ + O2 + 4e- 2H2O

ii). In neutral (or) alkaline medium, hydroxide ions are formed.

2H2O + O2 +4e- 4OH-

Then Iron ions (Fe2+) form anode combine with hydroxyl ions from cathode to form iron

hydroxide on the surface, b/w the anode and cathode areas.

Fe2+ + 2OH- Fe (OH) 2

OH- OH- Fe2+ Fe2+

Iron Metal

O2

H2O

Electrons

Cathodic region

Anodic region

Engg.Chemistry

SVCE Page 3

Iron hydroxide further reacts with oxygen and water forming hydrated iron oxide which is the

corrosion product [Rust].

4Fe (OH) 2 + O2 + 2H2O 2[Fe2O3.3H2O]

Rust

Types of Corrosion:-

Differential Metal Corrosion:-

Differential metal corrosion occurs when two dissimilar metals are in contact with each

another and exposed to a corrosive conducting medium, the metal with lower electrode potential

acts as anode undergoes oxidation and gets corroded. and the other metal with higher electrode

potential acts as cathode. Undergo reduction & protected from corrosion. This type of corrosion

is known as galvanic corrosion (or) differential metal corrosion.

The rate of corrosion depends mainly on the difference in potential b/w two metals.

Higher the difference faster is the rate of corrosion.

The reactions may be represented as,

At anode: - M Mn+ + e-

At cathode:- reduction reaction takes place, depending upon the nature of the environment.

2H+ + 2e- H2 (or)

2H2O + O2 +4e- 4OH-

Ex:-i). When iron is in contact with copper [0.34V], iron [-0.44V] becomes anodic and

undergoes corrosion whereas copper becomes cathodic and remains unaffected.

ii). Tin coating copper vessel.

iii). Steel pipe connected to copper plumbing.

iv). Bolt and nut made of different metals.

Differential Aeration Corrosion:-

When a metal is exposed to different concentrations of air (or) oxygen, part of the metal

exposed to lower concentration of oxygen becomes anodic and undergoes corrosion. Whereas,

other part of the metal exposed to higher concentration of oxygen becomes cathodic and remains

unaffected. This kind of corrosion is called as differential aeration corrosion.

Ex:- Iron rod partially immersed in Nacl solution, part of the metal immersed in solution is

exposed to lower concentration of oxygen becomes anodic and undergoes corrosion. Whereas part

Fe Metal Cu Metal

Anode Cathode

Zn metal Fe Metal

Anode Cathode

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Rust

Water

More oxygen,

(Cathode)

Less Oxygen

(Anode)

of the metal outside Nacl solution, is exposed to more oxygen becomes cathodic and remains

unaffected.

The anodic and cathodic reactions are

At Anode:- Fe Fe2+ + 2e-

At Cathode:- 2H2O + O2 +4e- 4OH-

Fe2+ + 2OH- Fe (OH) 2

Other Examples:-

1. Part of the nail inside the wall undergoes corrosion.

2. When a dust particle sits on a metal bar, the part under the dust undergoes corrosion.

3. Partially filled iron tank undergoes corrosion inside water.

Typical examples of differential aeration corrosion are the Water-line corrosion & Pitting

corrosion.

a). Water-line Corrosion:-

It is observed in steel (or) Iron water tanks partially filled with water.

When a steel tank is partially filled with water for a long time, the inner portion of the

tank below the water line is exposed only to dissolve oxygen, whereas the portion above the

water line is exposed to more oxygen. Thus the portion below the water line acts as anode and

undergoes corrosion. The upper portion acts as cathode and is unaffected.

A distinct brown line is formed just

below the water line due to the deposition of

rust.

The cell reactions are

At Anode: - M Mn+ +ne-

At Cathode: - 2H2O + O2 +4e- 4OH-

Finally, the ions combine to form corrosion product.

Less O2, (Anode)

Nacl solution

More O2,

(Cathode)

Iron

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Ex: - Ships which remain partially immersed in sea water for a long time undergo water line

corrosion.

b). Pitting Corrosion:-

This type of corrosion is observed when dust particles (or) oil drops deposited over the

metal surface.

Pitting corrosion is due to

i). Metal surface is not homogeneous. ii). External environment is not homogeneous.

iii). Crystallography directions are not equal in the reactivity.

iv). Environments are not uniform with respect to concentration.

Pitting corrosion results when the portion of the metal covered by dust which is less

aerated becomes anodic and undergoes corrosion and form pit. The remaining area of the metal

which is exposed to higher concentration of oxygen becomes cathodic and remains unaffected.

Once a small pit is formed the rate of corrosion increases because formation of small

anodic area [pit] to corrode faster because accepting

electrons from the cathodic area increases.

The cell reactions are

At Anode: - Fe Fe2+ + 2e-

At Cathode: -1

2O2 + H2O + 2e- 2OH-

Net reaction: - Fe2+ + 2OH- Fe (OH) 2

Factors affecting the rate of corrosion:-

Several factors affect the rate of corrosion of metals. These are broadly classified as

primary factors which are due to the metal and secondary factors which are due to the

environment.

Primary Factors:-

1. Nature of Metal:-

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• The position of the metal in the galvanic series decides the rate of corrosion and extent

of corrosion.

• The metals with lower e-de potential values are more reactive and more susceptible for

corrosion than the metal with higher e-de potential values. Ex:- Zn, Mg,etc….

• The rate of the corrosion depends upon the difference in the position of the metals in the

galvanic series, higher the difference, faster is the corrosion at anode.

Ex: - Li corrodes faster than Mg, Zn corrodes faster than Fe, Cu corrodes faster than Ag.

2.Nature of the Corrosion Product:-

The product of the corrosion is usually the oxides of the metals. The nature of

oxide layer determines the corrosion rate.

• If the corrosion product formed is insoluble, stable, uniform, non-porous and non-volatile,

it acts as a protective film and prevents further corrosion of metal because it acts as barrier

b/w the fresh metal surface and the corrosive environment.

Ex: - Meals like Al, Ti, Pt and Cr the oxide film formed acts as protective film hence the

corrosion is controlled.

• If the corrosion product formed is soluble, unstable, non-uniform, porous and volatile in

nature continues the corrosion process because it acts as non-protective film.

Ex: - In case of metals like Fe, Zn and Mg the oxide film formed acts as non-protective

film and corrosion is continued till the metal is completely destroyed.

3. Anodic and Cathodic Areas: -The rate of corrosion is highly influenced by the relative area

of anode and cathode.

• If the metal has small anodic area and large cathodic area, more intense and faster is the

corrosion.

• If the metal has, large anodic area and small cathodic area, decrease the rate of corrosion.

Ex: -A broken coating of tin on iron surface, a small

exposed part of iron acts as anode and rest of large

tin coated area act as cathode. Because of small anodic

area to cathodic area the rate of corrosion is high.

Secondary Factors:-

1.PH:-

Fe-metal

[anode]

Tin-metal

[][[[cathode]

Small anodic area

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Acidic media are generally more corrosive than alkaline (or) neutral media. The PH of the

solutions decides the type of cathodic reaction.

• The rate of corrosion increases with decreases in PH

Ex: -iron does not undergo corrosion at PH greater than 10, this is due to the formation of

protective coating of hydrous oxides of iron. If PH is less than 3, corrosion occurs fastly

• The rate of corrosion decreases with increase in PH

Ex: - Zn suffers from corrosion even in the presence of mild acidic medium, whereas

corrosion is minimum at PH=11.

2.Temperature: - The rate of chemical reaction increases with increase in temperature.

• The rate of corrosion increases with increase in temperature.

• Increase in temperature increases the ionic conductivity of the medium increases, decreases

hydrogen voltage hence increases the rate of corrosion.

• A Corrosion resistant passive metal becomes active at high temperature and increase the

rate of corrosion with increasing temperature.

Ex: - Caustic embrittlement in high pressure boilers.

3.Conductance:-

• The rate of corrosion is directly proportional to the conductance medium.

• The rate of corrosion increases in the presence of conducting species in the atmosphere

because corrosion is in electrochemical phenomenon.[

Ex: -i). The corrosion of metal structures is faster within the clay and mineralized soils

than in dry sandy soils.

ii). The rate of corrosion is more in ocean water and less in river water.

Note:- higher the conductivity of the medium, faster the ion can migrate between the anodic

and Cathodic regions of the cell.

Corrosion Control Methods:-

Corrosion can be controlled by preventing the formation of galvanic cells on the surface

of metals.

The methods to control corrosion can be classified as,

1. Design & Selection of materials.

2. Protective coatings. i). Inorganic coatings. ii). Metal coatings.

3. Cathodic Protection.

1. Protecting Coating:-

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Corrosion is prevented by the application of protective coating on the surface of

metal, there by the metal surface is isolated from the corrosive environment. Important

types of protective coating are,

a. Metal coating. b. Inorganic coating.

a.Metal coating:-

“The process of coating base metal with a layer of protective metal is known as metal

coating”.

There are two types of metal coating,

1. Anodic coating. 2. Cathodic coating.

1.Anodic coating;-

“The coating metal is anodic to base metal is called anodic coating”.

Ex: - Galvanization.

Galvanization:-

“The process of coating zinc on the base metal [Fe, Steel] surface by hot dipping is known

as galvanization”.

The galvanization process is carried out as follows

➢ The metal surface is washed with organic solvent[CCl4, Toulene,Benzene] to remove

organic matters.

➢ The metal surface is treated with dil.H2SO4 to remove rust and other deposits.

➢ Then it is well washed with water & it is air dried by passing with hot air.

➢ The metal is treated with a mixture of zinc chloride and ammonium chloride solution

which prevents the oxidation of the coated metal.

➢ Then the metal is dipped in molten Zinc at 4500c

➢ Excess of zinc on surface is removed by passing a pair of hot rollers, which removes

excess of zinc and produced thin coating

Iron Sheet Rollers Drier

Galvan

ized

Sheet

Organic Dil.H2SO4 ZnCl2 +NH4Cl Molten Zn Excess Zn

solvent flux [450°𝐶]

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Application: - Galvanized materials are used in fencing wire, buckets, bolts, nuts, nails, screw

etc.

Note:- Galvanized sheets cannot be used for preparing (or) storing food because zinc dissolves in

acidic medium and forms toxic compounds.

b. Inorganic coating:-

These coatings are produced at the surface of the metal by chemical (or) electrochemical

reactions.

Ex: - Anodizing and Phosphating.

Anodizing:-

Anodizing coatings are generally produced on non-ferrous metals like Al, Zn, Mg and

their alloys by anodic oxidation processes in which the base metal is made as anode.

Anodizing of Aluminum:-

When aluminum metal is made anodic in an electrolytic bath with H2SO4 (or) chromic

acid as the electrolyte, a thin layer of Al2O3 is formed on the surface. This process is called

Anodizing (or) Anodic oxidation of Aluminum.

The porous coating is obtained by anodic oxidation; it is carried out by making it anode

in an electrolytic bath containing a suitable acid like chromic acid (or) H2SO4 at 350-400c. A

plate of lead (or) stainless steel is made the cathode. When current of moderate density is passed,

the O 2 liberated at the anode combines with it to form oxide which takes the form of thick film

Al2O3 deposits on the surface of the object.

Over all reaction:- 2Al + 3H2O Al2O3 + 3H2

The coating is slightly porous and it is sealed by

dipping in hotwater. Al2O3 gets hydrated to Al2O3.H2O

which occupies more volume and

hence protects the metal from corrosion.

Application:- Metals such as Al, Mg, Ti etc are

anodized to control corrosion.

Temp-35-

450C

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Cathodic Protection:-

Cathodic protection is the technique of offering protection to a specimen against

corrosion by providing electrons from an external source.

There are two important methods of cathodic protection.

1. Sacrificial Anode Method.

2. Impressed Current /Voltage Method.

1. Sacrificial Anode Method:-

Sacrificial anode method involves the use of a metal which is anodic to the

specimen.

In this method the metallic structure to be protected is connected to a more anodic metal

using a metallic wire. More active metal gets corroded, while the parent metallic structure is

protected from corrosion.

Ex: - when steel metal to be protected, it may be connected to a block of Mg of Zn , in

such case, steel acts as cathode and is unaffected. Mg or Zn act as anode and undergo sacrificial

corrosion. When the sacrificial anode gets exhausted, it is replaced with new ones.

The commonly used sacrificial anodes are Mg, Al, Zn, and their alloys.

Ex: - 1. Protection of ship’s hull by fixing Zinc plates.

2. Protection of an underground pipeline with a magnesium anode.

Electrical Conductor

Steel Pipe [Cathode]

Mg Block

[Anode]

Impressed Current Method:-

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In Impressed current method the electrons are supplied from a source of direct

current [Battery].

In Impressed current method, the metal to be protected is connected to the negative

terminal of an eternal D.C. power supply. The positive terminal is connected to an inert electrode

such as graphite. Under these conditions, the metal acts as cathode and hence does not undergo

corrosion. The inert electrode acts as anode, but it does not undergo corrosion because it is inert.

Battery

Advantages:-

1. Requires low installation cost and minimum

maintenance cost after installation.

2. It is used for protecting water storage tanks

and oil pipe lines.

Protected Metal

Inert Anode

Metal Finishing

The term metal finishing covers a wide range processes carried out to modify the surface

properties of a metal by deposition of a layer of another metal (or) polymer (or) by the formation

of an oxide film.

Definition:-

Metal finishing is the process of deposition of a layer of the metal on the surface of

substrate.

Technological Importance of Metal Finishing:-

Metal Finishing is carried out to obtain technologically important surface properties,

these properties are

• A decorative appearance.

• An improved corrosion resistance.

• An improved heat resistance.

• An improved surface hardness.

• To provide good electrical and thermal conducting surface.

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• To increase good thermal resistance.

• To increases good optical reflectivity.

Important Techniques of Metal Finishing:-

1. Electroplating.

2. Electrolessplating.

3. Metal Cladding

4. Metal Spraying

Electroplating:-

“Electroplating is a process of electrolytic deposition of a metal on the surface of another

metal by electrolysis”.

(OR)

Electroplating is the deposition of a metal by electrolysis over the surface of a substrate.

The substrate may be a metal, a polymer, a composite.

Theory of Electroplating:-

Electroplating is achieved by passing an electric current through an electrolytic solution

con

taining metal ions and electrodes.

The process of electroplating is made of four important

parts.

1. Electroplating bath solution:- it contains a suitable

salt solution of the metal being plated. It also contains

other additives.

2. Anode:- it is positive elect rode in the electrolysis,

where metal ions are created. It may be inert electrode,

it should be electrically conducting.

3. Cathode: - it is negative electrode in the electrolysis,

where metal ions gets deposited and it is an article to

be plated.

4. DC-Power supply: - the +ve terminal of the power

DC power

Supply

Cathode

Electroplated

Metal layer

Electrolyte

Anode

ne- ne-

Engg.Chemistry

SVCE Page 13

supply is connected to the anode and the –ve terminal is connected to the cathode. The

electricity that passes from the anode to the cathode.

Reactions at Anode & Cathode during Electroplating:-

At Anode oxidation takes place M Mn+ + ne- Ex:-Cu Cu2+ + 2e-

When anode used is an insoluble [inert] material, Evolution of oxygen takes place

H2O 1

2𝑂2 + 2𝐻+ + 2𝑒−

At Cathode, Reduction occurs; the metal gets deposited on the cathode surface.

𝑀 → 𝑀𝑛+ + 𝑛𝑒− Ex: - Cu2+ + 2e- Cu

Principles of Metal Finishing:-

The fundamental principles governing metal finishing are

a. Polarization

b. Decomposition potential

c. Overvoltage.

Polarization:-

Polarization is an electrode phenomenon.

It is defined as “a process in which there is the variation of electrode potential due to

slow supply of ions from the bulk of the solution to the surface of electrode”.

The electrode potential is given by Nernst’s equation

E = Eo + 0.05691

𝑛 log [Mn+]

Explanation: - Consider an Electrolytic cell under operation. When current is being passed,

positive ions are produced at the anode and are consumed at the cathode. If the diffusion of ions

in the electrolyte is slow [due to variation in current density, temperature or PH] there will be an

accumulation of positive ions in the vicinity of anode instead of cathode takes place. As a result

there will be a decrease of ions in the vicinity of cathode takes place. Under these conditions, the

anode and cathode are said to be polarized.

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Polarization depends on

• Nature of Electrode

• Electrolyte concentration and its conductivity.

• Products formed at electrodes.

• Temperature.

• Rate of stirring of the electrolyte.

Decomposition Potential:-

Decomposition potential is defined as “The minimum external potential required for the

continuous electrolysis of an electrolyte”.

The decomposition potential is determined by using an electrolytic cell as shown in fig.

The cell consists of two Pt- e-des immersed in the electrolyte. The voltage is varied by

moving the contact maker D along the wire AB and the current passing through the cell is

measured using an ammeter.

If dilute solution of acid (or) base taken in the cell, at low voltages no reaction is found to

occur and when the voltage is slightly higher than 1.7v, a sudden evolution of H2 and O2 at the

electrode is noted. This is accompanied by increase in the current. Thus the applied voltage of

1.7v is the decomposition potential for dilute acids and bases.

A plot of current v/s voltage shows gradual increase of current with increase in applied

voltage in the beginning and large increase in current above ED and the decomposition voltage is

determined by extrapolation of the curve as shown in the above figure.

Over Voltage:-

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Over voltage is defined as “the excess voltage that as to be applied above the

theoretical potential for continuous electrolysis”.

η= Experimental decomposition potential-Theoretical decomposition potential

Ex: - the theoretical potential of oxygen at platinum electrode is 1.23v but the actual

decomposition potential of oxygen is 1.68v. The excess 0.45v is the overvoltage of oxygen on

platinum e-de surface.

Factors affecting Over Voltage:-

a. Nature of electrode

b. Current density

c. Temperature.

d. Impurities

Plating Process:-

The plating process is carried out by pretreating (or) surface preparation of the object

followed by electrolysis.

Pretreatment (or) Surface preparation:-

It is very much necessary to clean the surface of the base metal before electroplating in

order to get a good deposit.

Surface cleaning involves following steps.

1. Removal of organic substances: - Solvent and Alkali cleaning.

2. Removal of inorganic substances: - mechanical and Pickling.

3. Rinsing with water.

1. Solvent Cleaning:-

It is used to remove oils, greases, etc.. from the surface. For cleaning organic solvents

such as Benzene, Toluene, Carbon tetra chloride etc.. are used.

Ex: - Trichloroethylene was previously used for removing paints and resins.

2. Alkali Cleaning:-

Residual oil & grease from the surface is removed by treatment with alkaline

solutions. [NaOH, Na2CO3, etc..].

3. Mechanical cleaning:-

Mechanical cleaning involves removal of the oxide layer (or) rust and other

inorganic deposits on the metal surface. The simple methods involve the hand cleaning

with sand paper, bristle brush, polishing tools etc…

4. Pickling (or) Acid cleaning:-

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It is used to remove oxides, rust and other contaminants from the metal surface

by immersing in an acid such as dilute Hcl (or) H2SO4.

5. Rinsing with water:-

The object is finally rinsed with deionized water preferably in hot conditions and

dried before it is subjected to electroplating.

Electroplating of Chromium:-

The surface of the object is cleaned thoroughly; organic substances are

removed by solvent cleaning and alkali cleaning. Inorganic substances are removed by

mechanical cleaning and picking. Finally the surface is washed with deionized water. Then

chroming plating is done under the following conditions.

In the field of electroplating two types of chromium are employed: decorative &

hard.

Plating conditions Decorative chromium

plating Hard chromium plating

1. Plating bath composition Chromic acid (H2CrO4) +

H2SO4

in the weight ratio 100 : 1

Chromic acid (H2CrO4) +

H2SO4

in the weight ratio 100 : 1

2. Operating temperature 45-55oC 45-55oC

3. Current density 145 – 430 A/ft2 290 – 580 A/ft2

4. Current efficiency 10 – 15 % 17 – 21 %

5. Anode Insoluble anode: Pb-Sb or Pb-

Sn alloy coated with PbO2.

Insoluble anode: Pb-Sb or Pb-

Sn alloy coated with PbO2.

6. Cathode Object to be plated Object to be plated

7. Anodic reaction Liberation of oxygen: H2O 1/2 O2 + 2H+ + 2e-

Liberation of oxygen: H2O 1/2 O2 + 2H+ + 2e-

8. Cathodic reaction Cr3+ + 3e- Cr Cr3+ + 3e- Cr

In chromic acid, chromium is present in 6+ oxidation state. It is first reduced to 3+ satate

by a complex anodic reaction in the presence of sulphuric acid. The Cr3+ then gets reduced to Cr

on the surface of the substrate.

For a good deposit, the Cr3+ concentration must be low. The PbO2 oxidizes a part of Cr3+

to Cr6+ thus reducing the concentration of Cr3+.

2Cr3+ + 3O2 2CrO3 + 6e-

Chromium anodes are not used in Cr-plating, because

• If chromium dissolves at anode, there will be a high concentration of Cr3+ in solution; in

such case a black deposit is obtained.

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• In acidic solutions, chromium may undergo passivation.

ElectrolessPlating:-

Electrolessplating is the deposition of a metal without the use of electrical energy.

It is defined as “the process in which metal is depositing over a substrate by controlled

chemical reduction of metal ions by a suitable reducing agent without using electrical energy”.

The Electroless plating can be represented as,

Mn+ + Reducing agent M + oxidized product.

Composition of Electroless Plating bath:-

▪ Metal salts to provide Mn+ for deposition. Ex:- NiCl2, CuSo4

▪ Reducing agent to reduce metal ions into metal atoms.

Ex:- sodium hypophosphite, Formaldehyde.

• Complexing agents to form complex compounds with metal ions.

Ex: EDTA, sodium Succinate

• Accelerators to increase rate of plating.

• Stabilizer to give more stability to solution.

• Buffer to control the PH. Ex: Sodium Hydroxide + Rochelle salt.

Surface Preparation:-

Before Electroless plating the surface of the substrate should be catalytically activated as

follows.

• Acid Treatment.

• Electroplating a thin layer of the metal followed by heat treatment.

• For non-conducting surfaces such as plastics (or) printed circuit boards, the surface is

treated with Sncl2 and Palladium chloride solution alternately.

Electroless Plating of Copper:-

Before Electroless plating the plastic board is degreased and etched in acid. It is

activated by dipping in SnCl2 / HCl at 250c followed by dipping in PdCl2.

Electroless plating is done under the following conditions,

Plating bath solution Copper Sulphate

Reducing agent Formaldehyde

Complexing agent and exaltant EDTA

Buffer Sodium Hydroxide[PH=11]

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Temperature 250c

Anode Reaction 2HCHO + 4OH- 2HCOO- + 2H2O + H2 +2e-

Cathode Reaction Cu2+ +2e - Cu

Net Reaction 2HCHO + 4OH- + Cu2+ 2HCOO- + 2H2O + H2 + Cu

Typical application of Electroless copper plating is printed circuit boards,

particularly double sided boards in which plating through holes is required.

Electroless Plating of Nickel:-

Before Electroless plating the non-metallic materials are degreased and etched in

acid. It is activated by dipping in SnCl2 / HCl at 250c followed by dipping in PdCl2.

Before Electroless plating the metallic materials are degreased and etched with acid.

Plating bath solution Nickel Chloride [or ]Nickel Sulphate

Reducing agent Sodium Hypophosphite

Complexing agent and exultant Sodium Succinate

Buffer Sodium Acetate [PH=4.5]

Temperature 930c

Anode Reaction NaH2PO2 + H2O NaH2PO3 + 2H+ + 2e-

Cathode Reaction Ni2+ +2e - Ni

Net Reaction NaH2PO2 ++ H2O + Ni2+ NaH2PO3 + 2H+ + Ni

Distinctions b/w Electroplating and Electrolessplating:-

Property Electroplating Electrolessplating

Driving Force Electric Current Autocatalytic Redox Reaction.

Anode Separate Anode Catalytic surface of substrate

Cathode Article to be plated Catalytically active surface.

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Reducing agent Electrons Chemical reagent

Anode reactant Metal (or) H2O Chemical reagent

Applicability Only to conductors Conductors and non-conductors.

Throwing Power Low High.

Most Probable Questions:-

1. Define Corrosion? Explain Electrochemical theory by taking Iron as Example.

2. Explain Differential metal & Differential aeration Corrosion with Example.

3. Explain Differential aeration Corrosion with Typical Examples.[Water line & Pitting

Corrsion]

4. Explain the Factors affecting rate of corrosion.[All Factors].

5. Explain Galvanizing Process.

6. Explain Anodizing of Aluminum.

7. Define Cathodic Protection? Explain Sacrificial anode & Impressed Current method.

Metal finishing

1. Define Metal Finishing?Write any five Technological importance of Metal Finishng.

2. Explain the following Principles governing Electroplating Process

a. Polarization b. Decomposition Potential c. Over Voltage

3. Define Electroplating? Explain Electroplating of Chromium.

4. Define Electrolessplating? Expalin Electrolessplating of Copper.

5. Define Electrolessplating? Expalin Electrolessplating of Nickel.

6. Mention difference between Electroplating & Electrolessplating Process.

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MODULE-III :

ENERGY STORAGE SYSTEMS

Chemical Fuels: Introduction, classification, definitions of CV, LCV, and HCV, determination

of calorific value of solid/liquid fuel using bomb calorimeter, numerical problems. Knocking of

petrol engine – Definition, mechanism, ill effects and prevention. Power alcohol, unleaded

petrol and biodiesel.

Fuel Cells: Introduction, differencesENGINEERINGbetweenconventionalCHEMISTRYcell

and fuel cell, limitations & advantages. Construction, working & applications of methanol-

oxygen fuel cell with H2SO4 electrolyte, and solid oxide fuel cell (SOFCs).

Solar Energy: Photovoltaic cells- introduction, construction and working of a typical PV cell.

Preparation of solar grade silicon by Union Carbide Process/Method. Advantages &

disadvantages of PV cells.

(RBT Levels:L3)

Chemical Fuels

Introduction:-

Energy is an important aspect of human activity. Energy is a capacity to do work. There

is various forms of energies like electrical energy, chemical energy, thermal energy, mechanical

energy, etc…..

Fuels are main source of chemical energy. In this chapter we will deals with chemical

energy source.

The chemical energy sources are broadly classified into two types namely.

a. Fuels: - Ex: - Coal, Petroleum, Natural gas, Biomass, Uranium etc….

b. Non-Fuels:- Ex: - Solar, Wind, Tindal, Hydroelectric, etc…..

Definition of Fuel:-

Fuel is defined as “A naturally occurring (or) an artificially manufactured combustible

carbonaceous material, which serves particularly as a source of heat and light”.

Definition of a Chemical Fuel:-

“A chemical fuel is a substance, which produce a significant amount of heat and light

energy when burnt in air (or) oxygen”.

Classification of Fuels:-

On the basis of their origin fuels are classified as Primary and Secondary fuels.

1. Primary Fuels: - Fuels which occur naturally is called Primary fuels.

Ex: - Wood, Coal, Petroleum, Natural gas, etc….

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2. Secondary Fuels: - Fuels which are derived from primary Fuels are called Secondary

Fuels.

Ex: - Charcoal, Coke, Petrol, Diesel, etc……

On the basis of Physical state fuels are classified as Solid, Liquid, Gaseous fuels.

Physical State Primary Fuel Secondary Fuel

Solid Wood, Coal Charcoal, Coke

Liquid Petroleum Petrol, Diesel

Gas Natural gas LPG

Calorific Value:-

It is defined as “The total quantity of heat liberated, when a unit mass (or) unit volume of

the fuel is burnt completely in air (or) oxygen”.

Unit of Calorific value:-

For Solids, it is expressed in JKg-1 [joules per Kg]

For liquids it is expressed in Jm-3 [joules per meter cube].

Grass Calorific Value (or) Higher Calorific value:-

“The total amount of heat produced, when unit mass (or) volume of the fuel has been

burnt completely and the products of combustion have been cooled to room temperature”.

QGrass = Sensible heat + Latent heat of condensation of water.

Net Calorific value (or) Lower calorific value:-

“The amount of heat liberated when a unit mass (or) volume of the fuel is burnt

completely in air (or) oxygen and the products of combustion are permitted to escape”.

𝑄𝑁𝐸𝑇 = 𝑄𝐺𝑟𝑎𝑠𝑠 − 𝐿𝑎𝑡𝑒𝑛𝑡 𝐻𝑒𝑎𝑡 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟 𝑣𝑎𝑝𝑜𝑢𝑟 𝐹𝑜𝑟𝑚𝑒𝑑

𝑄𝑁𝐸𝑇 = 𝐺𝐶𝑉 − [9𝑋 𝑚𝑎𝑠𝑠 𝑜𝑓 𝐻2 𝑋 𝑙𝑎𝑡𝑒𝑛𝑡 ℎ𝑒𝑎𝑡 𝑜𝑓 𝑆𝑡𝑒𝑎𝑚]

𝑸𝑵𝑬𝑻 = 𝑮𝑪𝑽 − [𝟎. 𝟎𝟗𝑿 % 𝑯𝟐 𝑿 𝟐𝟒𝟓𝟒]𝑲𝑱/𝑲𝒈

Determination of Calorific value of Solids (or) Liquids using Bomb Calorimeter:-

Principle:-

A known weight of a liquid (or) solid fuel is completely burnt in excess of oxygen and

the liberated heat is absorbed by a known weight of water & Calorimeter. Thus the heat liberated

by the fuel is equal to heat absorbed by the water and the calorimeter. By recording the rise in

temperature of water and knowing specific heat of water, calorific value is calculated.

Construction:-

▪ The Bomb calorimeter consists of a stainless steel vessel with an airtight lid. This vessel

is called Bomb.

▪ The bomb has an inlet valve for providing oxygen atmosphere inside the bomb and an

electrical ignition coil for starting of combustion of fuel.

Engg.Chemistry

SVCE Page 3

▪ The bomb is placed in a insulated copper calorimeter.

▪ The calorimeter has a mechanical stirrer for dissipation of heat and a thermometer for

reading the temperature.

Working:-

▪ A known weight of the fuel in the form of pellet is taken in a crucible and placed inside

the bomb. The lid is close tightly.

▪ The Bomb is kept inside a copper calorimeter containing a known weight of water. Initial

temperature [t1] of water is noted after stirring.

▪ Oxygen is pumped into the bomb through oxygen valve.

▪ The fuel is ignited using electric current and liberating heat is absorbed by water and

calorimeter.

▪ The maximum temperature [t2] attained by water is noted.

Observation and calculation:-

Mass of fuel = m Kg.

Initial temperature of water = t°1C.

Maximum temperature of water = t°2C.

Rise in temperature of water = [t10-t2

0] C = 𝛥t°C.

Mass of water in the calorimeter = W1 Kg.

Water equivalent of calorimeter = W2 Kg.

Specific heat of water = S JKg-1C-1.

Heat released by the fuel = Heat absorbed by water and

Apparatus.

m𝑄𝐺𝑟𝑎𝑠𝑠 = (𝑊1 + 𝑊2)𝑋 𝑆 𝑋 ∆𝑡

𝑸𝑮𝒓𝒂𝒔𝒔 = (𝑾𝟏+ 𝑾𝟐)𝑿𝑺 𝑿 ∆𝒕

𝒎𝑲𝑱/𝑲𝒈.

Knocking in Petrol Engines:-

Knocking is defined as “The production of shock wave in an IC engine as a result of an

explosive combustion of fuel-air mixture, leading to a rattling sound”.

Mechanism of knocking:-

A. Under normal conditions there is a slow oxidation of the fuel. It involves following steps.

1. Slow combustion takes place due to the chain reactions. The overall reaction may be

represented as,

C2H6 +31

2O2 2CO2 + H2O.

B. Under knocking conditions, the rate of combustion is very high.

It involves following steps.

Thermometer

Lid

Wires for

ignition

Sample

Oxygen

B Stirrer

A

Engg.Chemistry

SVCE Page 4

1. Oxygen combines with hydrocarbon molecule forming peroxide.

H3C-CH3 + O2 H3C-O-O-CH3

Ethane Ethane- Peroxide.

2. The peroxides decompose rapidly to give a number of gaseous products.

H3C-O-O-CH3 H3C-CHO + H2O

Acetaldehyde.

H3C-CHO +1

2O2 HCHO + CO2 + H2O

Formaldehyde.

HCHO + O2 H2O + CO2.

3. Fast reaction leads to rapid increase of pressure. This results in knocking.

Ill Effects of Knocking:-

• It produces undesirable rattling sound.

• It increases fuel consumption.

• It reduces the efficiency of the engine.

• It damages the engine parts.

• It reduces the life of the engine.

Prevention:-

• Use of high quality gasoline [Petrol].

• Use of Antiknocking agents.

• By using critical CR.[Compression Ratio]

Antiknocking Agents:-

An important method of increasing the octane number and reducing the tendency of a

fuel to knock is by adding small amounts of certain compounds called Antiknocking agents.

(or)

Antiknocking agents are a chemical substance added to petrol to improve the Antiknocking

property of the petrol.

Ex:- TEL[Tetraethyl Lead], Power Alcohol, Unleaded Petrol etc……

Power Alcohol:-

When Ethyl Alcohol is used as an additive to motor fuels to act as a fuel for internal

combustion engines, it is called power Alcohol.

The addition of alcohol to petrol increases the octane number and alcohol blended petrol

posses better antiknock properties. Blends containing up to 25% alcohol with petrol are used.

The important raw materials for production of power alcohol are saccharine material

[such as molasses, sugar beets, sugar cane etc...], starchy materials [such as starch, potatoes,

cereal grains etc…], and cellulose material and hydrocarbon gases.

Engg.Chemistry

SVCE Page 5

Production of Ethyl alcohol from Molasses:-

Molasses is a dark coloured viscous fluid left after the crystallization of cane sugar from

cane juice. It contains 50-55% of total sugar out of which 30-35% is cane surar.[sucrose].

Molasses is diluted with water to bring down the concentration of sugar to 10-12%, PH is

kept acidic to favors the function of enzymes by adding sulphuric acid and allow for

fermentation for about 48-60 hours.

𝐶12𝐻22𝑂11 𝐶6𝐻12𝑂6 + 𝐶6𝐻12𝑜6

Glucose Fructose

𝐶6𝐻12𝑂6 2𝐶2𝐻5𝑂𝐻 + 2𝐶𝑂2

Glucose Ethyl alcohol

It is distilled to get ethyl alcohol which is mixed with water. Repeated distillation and

condensation can raise the alcohol content to 97.6% [Absolute alcohol].

Advantages:-

• Power output is high.

• Addition of alcohol reduces the emission of CO and volatile organic compounds.

• Ethanol is obtained from agricultural product.

• Ethanol is biodegradable.

• Ethanol contains higher percentage of oxygen than MTBE and hence brings about

complete & effective combustion of petrol. Therefore power alcohol has better

Antiknocking characteristics than unleaded petrol.

• Lubrication in case of power alcohol and pure petrol are same, hence required for

complete combustion is less.

Disadvantages:-

• The calorific value of alcohol is low hence alcohol blended petrol has low calorific value.

• Alcohol is easily oxidized to acids and it is able to cause corrosion.

• Air entering the cylinder needs to be regulated as less air is required for combustion.

• Alcohol absorbs moisture and as a result separation of alcohol and petrol layers takes

place especially at low temperature. To avoid this, blended agent like benzene (or)

toluene is used.

Unleaded Petrol:-

Petrol whose octane number is increased by the addition of substances other than lead

compounds is referred to as unleaded petrol.

In unleaded petrol methyl tertiary butyl ether is used as Antiknocking agents.

MTBE contains oxygen in the form of ether group. It supplies oxygen for the complete

combustion of the petrol in internal combustion thus reducing the formation of peroxy

compounds.

Engg.Chemistry

SVCE Page 6

Advantages:-

• It increases the efficiency of the engine.

• It avoids the lead pollution in the atmosphere.

• It allows the use of catalytic converters attached to the exhaust in automobiles.

• Reduce the air pollution due to CO, NOX, and unburnt Hydrocarbons.

Biodiesel:-

Biodiesel is a source of energy obtained from renewable sources of plant origin.

(Or)

Biodiesel is a mixture of monoalkyl esters of long chain fatty acids.

Biodiesel is synthesized by Transesterification process with methyl alcohol using NaOH

as a catalyst.

Transesterification is alcoholysis of the triglyceride oil in the presence of a base, resulting

mixture of monoalkyl esters of fatty acids is referred to as biodiesel.

CH2OCOR1

CHOCOR2

CH2OCOR3

+ 3CH3OHNaOH

60oC

CH3OCOR1

+

CH3OCOR2

+

CH3OCOR3

+

CH2OH

CHOH

CH2OH

Biodiesel GlycerolTriglyceride oil

Where R1, R2, R3 are the long chain fatty acids in the oil.

Advantages:-

• It is biodegradable and renewable.

• It is cheaper than diesel.

• It has higher cetane number compared to diesel.

• Use of biodiesel reduces greenhouse gases.

• Burns more efficiently than petroleum diesel.

• Biodiesel has higher lubricity hence it can reduce engine wear and hence prolong engine

life.

Disadvantages:-

• Calorific value of biodiesel is less compared to pure diesel.

• Purely obtained from plant origin & hence modification is required.

Numerical On Calorific Value:-

1. Calculate the calorific value of a sample of coal from the following data:

Mass of Coal = 0.6 g

Mass of water + water equivalent of calorimeter= 2200 g

Specific heat of water = 4.187 kJ kg-1oC-1

Rise in temperature = 3oC

Engg.Chemistry

SVCE Page 7

Solution:

(Note: In solving the problem, follow the steps given below:

1. Write the given quantities and convert them into appropriate units.

2. Write the equation.

3. Substitute the values.

4. Simplify using calculator if necessary.

5. Write the answer.

6. Write the units.)

Given: m = 0.6 g = 0.6 10-3 kg

w1 + w2 = 2200 g = 2.2 kg

s = 4.187 kJ kg-1oC-1

t = 3oC

Gross calorific value =( )

m

Δtsww 21 + kJ kg-1

= 3106.0

3187.42.2−

= 46057 kJ/kg

2. A 0.85 g of coal sample (carbon 90 %, H2 5%, and ash 5%) was subjected to combustion in

a bomb calorimeter. Mass of water taken in the calorimeter was 2000 g and the water

equivalent of calorimeter was 600 g. The rise in temperature was 3.5 oC. Calculate the

gross and net calorific value of the sample. (Given, specific heat of water = 4.187 kJ kg-1oC-1

and latent heat of steam = 2454 kJ kg-1 )

Solution: Given m = 0.85 g = 0.85 10-3 kg

% of hydrogen = 5%

w1 = 2000 g = 2 kg

w2= 600 g = 0.6 kg

t = 3.5 oC

s = 4.187 kJ kg-1oC-1

L = 2454 kJ kg-1

a) Gross C.V. = ( )

m

Δtsww 21 +

= ( )

31085.0

5.3187.46.02

−

+= 44825kJ kg-1

b) Calculation of N C V

NCV=GCV--(0.09HLatent Heat of steam) kJ Kg-1

=44825-(0.09 5 2454)

=44825 - 1104.3

=43720kJ kg-1

(Note: Latent heat of steam is the amount of heat energy liberated when one kg of steam is

converted into one kg liquid water.)

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SVCE Page 8

3. On burning 0.75g of a solid fuel in a bomb calorimeter the temperature of 2.5kg of water is

increased from 240C to 280C the water equivalent of calorimeter and latent heat of steam are 0.485

Kg and 4.2X587 KJ/Kg respectively , specific heat of water is 4.2KJ/Kg/0C, H2 2.5%.

Solution: Given

m = 0.75 g = 0.75 10-3 kg

w1+W2 = (2.5+0.485) kg = 2.985 kg

t = t2-t1=28-24=4 oC

s = 4.2 kJ kg-1oC-1

a. Gross C.V.=( )

m

tsww + 21 = KgkJKgJkX

XX/66864/

1075.0

2.44985.23

=−

b. Calculation of N C V

NCV = GCV-(0.09 H Latent Heat of steam) ……..kJ Kg-1

=66864-(0.09 2.54.2X587)

=66864– 554.715

=66309kJ kg

4. Calculate the gross and net calorific values by data given.

a) Mass of Coal = 0.7 g = 0.7 10-3 kg

b) Mass of water = 2.2 kg

c) Water equivalent of calorimeter = W2 = 0.25 Kg

d) Raising temperature = 3.2 0C

e) Specific heat of water = 4.187 kJ kg-1oC-1

f) Latent heat of steam = 580 calories / g [1 calorie = 4.187 kJ]

h)H2 =2%,

m = 0.7 10-3 kg

w1+W2 = 2.45 kg

t = 3.2 oC

s = 4.187 kJ/kg/oC

L = 580 calories / g=580 X 4.187kJ /Kg = 2428kJ/Kg

Solution:

GCV. = ( )

m

tsww + 21 = KgkJX

XX/44689

107.0

187.42.345.23

==−

b) Calculation of N C V

NCV=GCV-( 0.09H Latent Heat of steam )……..kJ Kg-1

= 46894- 0.09 2580 X4.187 kJ kg-1

=46894-437.122

=46456 kJ kg-1

5. On burning 0.96g of a solid fuel in bomb calorimeter the temperature of 3500g of H2O

increased by 2.70C water equivalent of colorimeter and latent heat of steam are 385 g and

587 cal/g respectively. If the fuel contains 5% H2 calculate its gross and net calorific value.

Given:

m=0.96g=0.96X10-3Kg

Engg.Chemistry

SVCE Page 9

W1=3500g=3500X10-3Kg

W2=385g= 385X10-3Kg

t=2.70C

Latent heat =587 cal/g = 587X4.187 kJ/Kg

S= 4.187 kJ/Kg/0C

H2 =5%,

Gross calorific value =( )

KgJkm

tsww/21 +

= 3

33

1096.0

7.2187.4)10385103500(−

−−

+ XX

= 45749.5 kJ/Kg

NCV = GCV- (0.09 H Latent Heat of steam) ……..kJ Kg-1

=45749.5- 0.09 5587X 4.187

= 44643 kJ/kg

6.On burning 0.85 ×10-3 kg of a solid fuel in a bomb calorimeter, the temperature of 2.1 kg water is

raised from 24OC to 27.6OC.the water equivalent of calorimeter and latent heat of steam are 1.1 kg

and 2454 kj/kg respectively. Specific heat of water is 4.187 kJ/kg. if the fuel contains 2% hydrogen

,calculate its gross and net calorific values.

m = 0.85 X 10-3 kg

W1=2.1Kg

W2 = 1.1 Kg

t1= 24OC

t2=27.6OC

s = 4.187kj/Kg

L = 2454Kj/Kg

KgkJX

XKgJ

m

tswwGCV /56746

1085.0

6.3187.4)1.11.2(/

)(3

21 =+

=+

=−

NCV = GCV- (0.09 H Latent Heat of steam)..kJ Kg-1

=56746- 0.09 2245 =56746-441.7 = 56304kJ kg-1

8. 0.75g of coal sample (carbon-90%, hydrogen 6%, and ash 4%) was subjected to

combustion in a bomb calorimeter. Mass of water taken in the calorimeter was 3500g and

the water equivalent of the calorimeter was 750g. The rise in temperature was found to be

3.3oC. calculate the grass and net calorific values of a sample.[ specific heat of water

4.187KJ/Kg/oC, latent heat of steam 2457 KJ/Kg] [Dec.2015/Jan-2016]

9. 0.75g of coal containing 2% hydrogen, when burnt in a bomb calorimeter, increased the

temperature of 2.7Kg water from 27.2oC to 29.7oC. If the water equivalent of calorimeter

is 1.2Kg. Calculate grass and net calorific value.[specific heat of water 4.187KJ/Kg/oC,

latent heat of steam 2457 KJ/Kg].[June/July-2016]

Engg.Chemistry

SVCE Page 10

10. A 0.6g of coal sample (carbon 90%, H2 3%, and ash 7%) was subjected to combustion

in a bomb calorimeter. Mass of water taken in the calorimeter was 2000g and the water

equivalent of calorimeter was 400g. the rise in temperature was 3oC. Calculate the grass

and net calorific value of the sample. Given specific heat of water is 4.187 KJ/Kg/oC and

latent heat of steam is 2454 KJ/Kg. [Dec.2016/Jan.2017]

11. A coal containg 92%, carbon, 7% hydrogen, 3% ash, is subjected to combustion in a

bomb calorimeter. Calculate GCV & NCV values. Given that mass of coal sample is

0.85g, mass of water in calorimeter is 2Kg, water equivalent of calorimeter is 0.75Kg, rise

in temperature of water is 2.5°C. [Dec.2017/Jan.2018]

Solar Energy Solar energy is one of the solutions for sustainable energy conversion processes. Solar

radiation coming from sun is highly useful in photosynthesis and is the major energy source for

ecosystem. Solar energy is non-depleting, non-polluting and available freely & can be utilized

for various applications.

Radiations from the sun constitute solar energy. It is a clean and renewable source of

energy available in abundance.

Production of solar grade Silicon [Union Carbide Process]:-

The following steps are involved in the preparation of solar grade silicon.

1. The hydrogenation of tetrachlorosilane through a bed of metallurgical silicon is carried

out in a fludized bed reactor.

3SiCl4 + 2H2 +Si 4 HSiCl3

2. The trichlorosilane is separated by distillation while the unreacted tetrachlorosilane is

recycled back to the hydrogenation reactor.

The purified trichlorosilane is passed through a fixed bed column filled with

quaternary ammonium ion exchange resin acting as catalyst. Trichlorosilane gets

converted into dichlorosilane.

2HSiCl3 SiH2Cl2 + SiCl4

The products are separated by distillation, tetrachlorosilane is recycled to the

hydrogen reactor and dichlorosilane is passed through a second fixed bed column filled

with quaternary ammonium ion exchange resin. Dichlorosilane is converted into silane.

3H2SiCl2 SiH4 + 2HSiCl3

3. The above products are separated by distillation and trichlorosilane is recycled to the

first bed column. Silane is further purified by distillation and then pyrolized to produce

polysilicon onto heated silicon seed rods mounted in a metal bell-jar reactor.

SiH4 Si + 2H2.

Si thus obtained can be further purified by Zone refining.

Engg.Chemistry

SVCE Page 11

Photovoltaic Cells:-

Photovoltaic cells are semiconductor device which convert solar energy into electrical

energy.

Photovoltaic cells can generate electricity as long as Sun light is available.

Construction and working of Photovoltaic cells:-

Photovoltaic cell is composed of a thin mater consisting of an ultra thin layer of

phosphorous doped [n-type] silicon on the top of boron doped [p-type] silicon. Hence P-n

junction is formed b/w the two.

• A metallic grid forms one of the electrical

contacts of the diode and allows light to

fall on the semiconductor b/w grid lines.

• An antirefractive layer b/w the grid lines

increase the amount of light transmitted to

the semiconductor.

• The cells other electrical contact is formed by a

metallic layer on the back of the solar cell.

Working:-

• When light radiation falls on the P-n junction diode, electrons-hole pairs are generated by the

absorption of the radiation.

• The electrons are drifted and collected at n-type end and the holes are drifted and collected at

the P-type end.

• When these two ends are electrically connected through a conductor, there is a flow of current

b/w the two ends through the external circuit. Thus Photoelectric current is produced and

available for use.

Advantages:-

• They are Environmental friendly.

• They need no recharging.

• They do not corrode.

• They operate at low temperature.

• No emission, no combustion.

• High public acceptance and excellent record.

• Low operating cost.

• No moving parts and so no wear and tear.

Disadvantages:-

• High installation cost.

• Energy can be produced only during the day time.

• Poor reliability of auxiliary elements including storage.

• Sun light is a diffuse, ie, it is relatively low density energy.

e-

P- Type layer

N-type layer

Antireflective layer

Metal grid

Sunlight

h+

e-

Metallic layer

Engg.Chemistry

SVCE Page 12

Fuel cell:- Fuel cells are the galvanic cells which converts chemical energy of fuels into electrical

energy by the combustion of fuels.

(OR)

Fuel cells are the galvanic cells which converts chemical energy of the fuels into

electrical energy through catalyzed redox reactions with elimination of minimum harmful

byproducts.

A fuel cell has two electrodes with catalysts and electrolyte. In this device fuel and

oxidizing agents are continuously and separately supplied to the respective electrodes at which

they undergo redox reaction to produce electrical energy.

Fuel cells produce electrical energy as long as fuels are supplied at respective electrodes.

It is represented by

Fuel Electrode Electrolyte Electrode Oxidant

At Anode, fuel undergo oxidation Fuel Oxidation product + ne-

At Cathode, Oxidant gets reduced Oxidant + ne- Reduction product

Difference b/w conventional cell (or) battery and Fuel cell:-

Battery Fuel cell

• 1. Batteries are energy storage devices. 1. Fuel cells are energy conversion devices.

• 2. The reactants and products from integral

parts of batteries.

2. In fuel cells there is continuous

movement of fuel, oxidant & reaction

products in and out of cells.

• 3. The active materials are mixture of complex

chemical compositions.

3. The active materials are fuel and oxidant.

• 4. Create chemical pollution in the atmosphere. 4. Less harmful biproducts discharged to

atmosphere.

• 5. Recharging of the cell is required.

5. Recharging of the fuel cell is not

required.

1. 6. Electrodes are relatively cheaper.

6. Electrodes are very costly.

Limitations of Fuel cells:-

▪ Fuel cells produce energy only as long as fuels and oxidants are supplied.

▪ Electrodes are very costly.

▪ Power output is moderate.

▪ Fuels in the form of gases and oxygen need to be stored in tanks under high pressure.

▪ Reactions are constantly supplied and the products are constantly removed from the cell.

Engg.Chemistry

SVCE Page 13

Advantages of the Fuel cells:-

▪ They operate very silently.

▪ Their power efficiency is high.

▪ The cells have high energy density.

▪ They are ecofrindly.

▪ Space required for fuel cell is less.

▪ Produce harmless biproducts.

▪ Produces direct current for a long time.

Methanol-Oxygen Fuel cell:-

Methanol is preferred as a fuel in fuel cells because of the following reasons.

• It has low carbon content.

• It possesses a readily oxidizable alcoholic group.

• It has high solubility in aqueous electrolytes.

Construction:-

▪ It consists of anodic and cathodic compartments and both the compartments contain platinum

electrodes.

▪ Methanol containing H2SO4 is passed through anodic compartments.

▪ Oxygen is passed through cathodic compartments.

▪ Electrolyte consists of sulphuric acid [3.7M]

▪ A membrane is provided which prevents the diffusion of methanol into the cathode.

Working: - At anode, CH3OH undergoes oxidation to CO2 liberates electrons, the liberated

electrons taken by oxygen gets reduced into water with liberation of energy at cathode..

Reactions:-

At Anode: - CH3OH + H2O CO2 +6H+ + 6e-

At Cathode: - 3

2O2 + 6H+ + 6e- 3H2O

Net reaction: - CH3OH + 3

2O2 CO2 + 2H2O

The cell potential is 1.21V at 25oc.

Cell Representation:-

CH3OH Pt H2SO4 Pt O2

Uses: -

• It is used in Military applications.

• USED as electric power source in space vehicles.

• Used in large scale power production.

O2 CH3OH

Excess Oxygen

and water

Cathode

Membrane

H2SO4 (electrolyte)

Anode

CO2

CO2

Engg.Chemistry

SVCE Page 14

Solid-Oxide Fuel Cell:

Solid-Oxide fuel cells are a class of fuel cell which use a solid oxide material as the

electrolyte.

Construction:-

• Anode of the cell made by a porous composite of Nickel-Zirconia cement.[NiZrO2]

• Cathode of the cell made by Strontium-doped Lanthanum Manganite.[Sr-LaMnO3]

• Electrolyte consists of Solid Yttria-Stabilized-Zirconia.

• H2 passed to Anode, it act as Fuel.

• O2 passed to Cathode, it act as Oxidant.

Working:-

• At anode, oxide ions combine with H2 in the fuel to form H2O, liberating electrons.

• Electrons flow from the anode through the external circuit to the cathode.

• At cathode, O2 supplied reacts with incoming electrons from the external circuit to from

oxide ions.

Anode: - H2 + O2- H2O + 2e-

Cathode: - 𝟏

𝟐O2 + 2e- O2-

Net reaction: - H2 + O2 H2O

As a result of the reactions at both the interfaces & the oxygen ion conductivity of the

electrolyte, electrons are transported from the cathode to the anode and a electricity is generated.

Electricity is produced as long as fuel & oxidant supplied.

Engg.Chemistry

SVCE Page 15

Most probable questions:-

Chemical Fuel:-

1. What are chemical fuels? How are they classified?

2. Define the term Calorific value of fuel. Explain the experimental determination

of calorific value of solid/liquid fuel using Bomb calorimeter.

3. Define Knocking. Explain Mechanism of Knocking of IC engine.

4. Write a note on 1. Power Alcohol 2. Unleaded Petrol 3. Biodiesel.

5. Define GCV & NCV and Numerical on Calorific value.

Solar Energy:-

1. Explain the Preparation of Solar grade Silicon by Union Carbide Process.

2. What are solar cells? Explain the construction and working of a Photovoltaic cell.

3. What are PV cells? Mention their advantages and limitations.

Fuel Cells:-

1. What are Fuel cells? How does a fuel cell differ from a battery? Give their advantages &

disadvantages.

2. What are Fuel cells? Describe the construction and working of CH3OH-O2 fuel cell.

3. What are Fuel cells? Describe the construction and working of Solid-Oxide fuel cell.

Engg. Chemistry

SVCE Dept.of Chemistry Page 1

Module-IV Environmental Pollution: Air pollutants: Sources, effects and control of primary air pollutants:

Carbon monoxide, Oxides of nitrogen and sulphur, hydrocarbons, Particulate matter, Carbon

monoxide, Mercury and Lead. Secondary air pollutant: Ozone, Ozone depletion.

Waste Management: Solid waste, e-waste & biomedical waste: Sources, characteristics &

disposal methods (Scientific land filling, composting, recycling and reuse).

Water Chemistry: Introduction, sources and impurities of water; boiler feed water, boiler

troubles with disadvantages -scale and sludge formation, boiler corrosion (due to dissolved O2,

CO2 and MgCl2). Sources of water pollution, Sewage, Definitions of Biological oxygen demand

(BOD) and Chemical Oxygen Demand (COD), determination of COD, numerical problems on

COD. Chemical analysis of water: Sulphates (gravimetry) and Fluorides (colorimetry). Sewage

treatment: Primary, secondary (activated sludge) and tertiary methods. Softening of water by ion

exchange process. Desalination of sea water by reverse osmosis.

(RBT Levels: L3)

Environmental Pollution and Water Chemistry Environment:-

The word Environment is a French word which means Surrounding.

It is the sum of total of all biotic [living] and abiotic [non-living] factors that surround

and potentially influence an organism.

Environment is the life support system that includes air, water & Land.

Components of Environment:-

1. Biotic components: it is the living component which includes Flora & Fauna.

2. Abiotic Components: it is the non-living components o the earth’s environment. This

includes atmosphere, lithosphere, hydrosphere, and biosphere.

3. Energy: it includes solar energy, geothermal energy, Hydro-electric energy, thermal

energy, nuclear-atomic energy, etc….

Atmosphere:-

The earth is surrounded by a blanket of air which is called as atmosphere.

or

The earth is enveloped by a gaseous layer called Atmosphere.

Engg. Chemistry


Chemical composition of the atmosphere:-

Air is a mixture of gases surrounding the earth’s surface. It consists of nitrogen[78%],

oxygen[21%] & other gases[1%] which includes CO2, argon & water vapour.

If the changes takes place in the environment by the natural process [or] man made

process, then pollution observed in environment.

Environmental Pollution:-

The word pollution is from Latin word Polutionem. This means makes darty.

Pollution is an undesirable change in the physical, chemical, biological characteristic of

water, air & land.

Causes of pollution:-

• Tremendous increase n human population.

• Rapid industrialization.

• Increase the exploitation of nature.

• Natural processes such as earth quake, forest fire, etc…

Sources of pollution:-

1. Natural sources: - the pollution originates from the natural climates such as wind, earth

quake, forest fire, etc…

2. Man made [or] Artificial sources: - the pollution originated due to the activities of man.

The substances which cause the pollution called as Pollutants.

The environmental pollution can be discussed under three categories. ie, air pollution, water

pollution, & soil[or] land pollution.

Air pollution:-

Air is colourless & odourless. But various pollutants from natural & ma made sources are

entering the atmosphere daily & disturb the dynamic equilibrium in the atmosphere. Which cause

the pollution.

Change [or] disturb in the normal properties of air are called air pollution.

[or]

The excessive discharge of undesirable foreign substances in to the atmospheric air,

which affects the quality of air & cause the damage to human, plants & animal lives, called as

Air pollution.

Engg. Chemistry


Air pollutants are classified in to two major categories.

1. Primary air pollutants.

2. Secondary air pollutants.

1. Primary air pollutants:-

Pollutants exit directly in nature & emitted directly to the atmosphere

called as primary air pollutants.

Ex: - CO, SO2, NO2, etc….

2. Secondary air pollutants:-

Pollutants which derived from primary pollutants & do not emitted directly to the

atmosphere called as secondary air pollutants.

Ex: - ozone, PAN [Peroxy acetlyl nitrate], Photo-chemical smog, H2SO4, HNO3, etc….

These pollutants do not have any identified sources & they are formed in the

atmosphere by some chemical [or] photochemical reactions.

Primary air pollutants:-

There are five primary air pollutants which cause air pollution.

1. Carbon Monoxide.

2. Oxides of nitrogen.

3. Oxides of sulphur.

4. Hydrocarbons.

5. Particulate Matter.

1. Carbon Monoxide:-

It is a colourless, odourless & tasteless gas which is injurious to our health.

It is a one of the toxic air pollutant.

Source:-

• Natural Source: - natural source such as forest fire, natural gas emission, volcanic

actions produces carbon monoxide in the atmosphere.

• Anthropogenic:-

(1) Incomplete combustion of fuel [or] carbonaceous compounds.

2C + O2 2CO

(2) Reaction b/w CO2 & carbonaceous material at high temperature gives CO.

CO2 + C 2CO

(3) Dissociation of CO2 at very high temperature gives CO

CO2 CO + C

(4) CO formed during the decomposition of Chlorophyll.

(5) Cigarette & Beedi smoke & domestic heat appliances are the other sources of CO.

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Effects:-

• Causes headache, visual difficulty, paralysis & even death.

• Causes Chromic effects include weakness, fatigue, increased red blood cells

[polycythemia] in blood.

• It reacts with hemoglobin to from carboxy-haemoglobin.

HbO2 + CO COHb + O2

• In the presence of CO reduces the oxygen carrying of blood.

• Causes serious effects on the cardio vascular system, there by causing heart diseases.

• High concentration of CO [100-1000PPM] can affect leaf drop, leaf curling, and

reduction in the leaf size in plants.

Control:-

• Modification of internal combustion engines.

• Development ofexhaust system reactors, which will complete the combustion process.

• Development of substitute fuels for gasoline which will yield low concentration of

pollutants upon combustion.

• Development of popllution free sources such as fuel cells to replace the internal

combustion engine.

2. Oxides of Nitrogen:-

Nitric oxide [NO], Nitrogen dioxide[NO2], and Nitrous oxide[N2O] are referred as

oxides of nitrogen.

NOx are formed at two stages during combustion.

1. The reaction of O2 with nitrogen compounds in the fuel, this is termed as Fuel NOx.

2. The reaction of N2 with N2 in combustion air, this is termed Thermal NOx.

Source:-

• Produced naturally by lighting, volcano & bacterial decay process.

• Produced by automobile exhaust, combustion of coal, oil, natural gas & gasoline.

• Other sources like acid manufacture, power plants, fertilizer industry, explosive

industries, etc…

• Basic reactions are

N2 + O2 2NO

2NO + O2 2 NO2

NO2 + O3 NO3 + O2

NO3 + NO2 N2O5

• Nitrous oxide produced by the denitrification bacteria in the soil. [N2O].

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Effects:-

• High concentration of NO2 causes inflammation of lung tissue, respiratory illness.

• NO2 reacts with H2O & O3 to form, HNO3, & N2O5, which cause acid rain.

• A use chromic effects like, cell membrane damage, stress on the heart.

• In sunlight nitrogen oxides combines with hydrocarbons from photochemical smog.

Which cause

i) Limits the visibility of roads,

ii) Cause eye irritation

iii) Cause difficulty in breathing

iv) Cause lung cancer, asthma & bronchitts.

Controls:-

• The exhaust emission from automobiles can be controlled by installing catalytic

converter in to the IC engine.

When exhaust gas passes through the converter, oxides of nitrogen are converted

into nitrogen & oxygen.

2NOx N2 + XO2

• Emission of NOx generated during the combustion process can be reduced by treating

the fuel gas.

A. Selective Catalytic Reduction: - In this process ammonia is injected into the fuel

gas. The NOx present in the fuel gas react with the ammonia & are converted to N2

& H2O.

B. Sorption: - treatment of fuel gas by injection of sorbents. [Ammonia, powdered

limestone, carbon] can remove NOx & other pollutants.

3. Oxides of Sulphur:-

Sources:-

• Natural process like Volcanic activity releases SO2, SO3, H2S, S & Particulate matter

in to atmosphere.

• Combustion of fossil fuels

• Combustion of sulphur containing fuels [coal] in thermal power plants, automobiles.

S + O2 SO2

• Oxygen formed by thermal decomposition of ozone oxidizes H2S in the atmosphere to

SO2.

H2S + 3[O] SO2 + H2O

• SO3 is formed by the oxidation of SO2 in the atmosphere by atomic oxygen [or]

molecular O2 [or] ozone.

SO2 + [O] SO3

SO2 +1

2O2 SO3

SO2 + O3 SO3 + O2

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Effects:-

• Cause the cardiac, respiratory & pulmonary diseases.

• Cause eye irritation, throat troubles.

• Cause the corrosion of metals.

• Damages of plant cells & membrane, chlorophyll, reduce crop yield.

• SO3 in air causes breathing discomfort & irritation to the respiratory track.

• SO2 & SO3 formed in the atmosphere can combine with water vapour forming H2SO3 &

H2SO4 mist. It causes the acid rain.

SO2 + H2O + H2SO3 SO3 + H2O H2SO4

• H2SO4 mist can damage natural & synthetic fibers.

• Cause the yellowing of paper & the loss of its mechanical strength.

Controls:-

• Low sulphur fuels can be used to reduce sulphur dioxide emission in to the atmosphere.

• SO2 containing gases are passed through ammonia solution, where ammonium sulphate is

obtained as a byproduct.

2NH4OH + SO2 (NH4)2SO3 + H2O

• Cairox method: - gas containing SO2 are treated with alkaline KmnO4 solution through

a spray, when oxidation of SO2 takes place.

2KmnO4 + 3SO2 + 4KOH 2MnO2 + 3K2SO4 + 2H2O

• Use clean sulphur free nuclear power to generate electricity.

• Use of natural gas reduces Sox emmition.

4. Hydrocarbons: -

Sources:-

• Anaerobic biological decay processes in nature.

• Bacterial decomposition of organic matter [or] sewage waste.

2(CH2O) CO2 + CH4

Org. Matter (HC)

• Automobile exhaust consisting of unburnt petrol.

• The industrial sources include pulp industry, petroleum refineries, coke-oven plants,

chemical industries, etc…

Effects:-

• Cause the carcinogenic effects on lungs.

• Inhalation of vapours of benzene, toluene etc.. causes much irritation to the mucous

membrane.

• Cyclic HC, affects nervous system.

• Methane cause narcotic effect in the human being.

• It causes swelling of lungs, cancer, irritation on eyes.

• Cause extensive damage to plant life.

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Control:

• HC from auto exhaust can be controlled by processes such as incineration, adsorption,

absorption, etc..

HC CO2 + H2O

• Using analytic converters

CH4+2O2 CO2+ 2H2O

5. Particulate matter:

The term particulate refers to solid particles and liquid droplets suspended in air.

Particulates are also referred as aerosols. They include smoke, dust, mist & spray. The size of

particulate matter may vary from 0.002 to 500mm.

Sources:

Dust:

• Main dust sources are mines, quarries, furnaces, power houses, automobiles, domestic

dust, natural winds etc…

• Crushing, grinding, and blasting of solid materials.

• Processing of materials like coal, cement, asbestos.

Smoke:

• Incomplete combustion of carbonaceous material.

• Emission sources like from exhausts of trains, roads, wood, coal, graters, power plants,

open fire, diesel engines, automobile gasoline engines etc…

Mist:

• Condensation of vapours.

• Dispersion of liquids,

• Chemical reactions forming liquid droplets.

Spray:

• Automization of liquid droplets.

Ash:

• Burning of coal which leaves behind a mixture of non combustible inorganic oxides.

Effects:

• Atmospheric dust causes allergic & respiratory diseases.

• Smoke causes cancer, coughing, nose blocking, heavy breathing.

• Lead as particulate affects children brain.

• Particulate of small size causes the damages in lung tissue.

• The acid & aldehyde particulates cause eye, noise & throat irritation.

• In plants absorption of CO2 is restricted.

• Deposition of toxic metals on soil makes it unsuitable for plant growth.

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Control:- the principle of control is based on the density, stickiness & electrical property of the

particulate matter. Some of the techniques used are

• Control of smoke during combustion:-

a. Use of suitable fuels which do not

produce much smoke. Eg:- coke

b. By maintain proper fuel air ratio.

c. Sufficient mixing of air & fuel.

d. Maintain sufficient ignition

temperature.

e. Providing sufficient space to permit time for

proper burning.

• Gravity settling chamber:-

This method used to remove large & heavier particles. Gas is

passed slowly into dust chamber in one direction, the heavy

particles get deposited. This method is used for preliminary

purification.

• Wet Scrubber:- The simplest type of wet scrubber is the spary tower.

When a particulate gas is passed into a chamber it comes in contact with

water spray. Water droplets capture particulate & settle down at the

bottom of the chamber.

• Fabric Filter: - particulate matters are filtered by passing through fabric filters made up of

cotton, wool & artificial fibers.

Mercury: -

Mercury is a naturally occurring element. It exists in three chemical forms.

1. Methyl Hg. 2. Elemental Hg. 3. Hg compounds[inorganic & Organic]

Sources:-

• Natural sources of mercury include volcanoes, natural mercury deposits & release from

the ocean.

• Man made sources include coal combustion, waste incineration, metal processing

industries.

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• From industries like paper industry, chemical industries, paint manufacturing units, etc…

• From Hg containg products such as batteries, thermometers, lamps, cosmetics,

pharmaceuticals, etc….

Effects:-

• Elemental & methyl Hg are toxic to the central nervous system.

• The inhalation of Hg vapours causes the damages in brain, heart, kidneys, lungs &

immune system of all ages.

• Methyl Hg causes minamata disease.

• Inorganic salts of Hg causes the corrosive to the skin, eyes & gastro intestinal tract.

• Different types of Hg compounds cause mercury loss, neuromuscular effects, headaches

& motor dysfunction.

Controls:-

• Promote the use of clean energy sources that do not burn coal.

• Eliminate mercury mining & use of mercury in gold extraction.

• By using efficient absorbents to minimize Hg in industrial effluent gases.

• Recovery & reuse of Hg compounds in industrial wastes.

• Using alternative materials for replacing Hg in electronic switches.

• Replacing CFL’s with LED lamps.

• Hg emission is controlled at the source by using fabric, filters, wet scrubbers etc…

Lead:-

Sources:-

• Automobile exhaust gases [combustion of lead containing gasoil].

• From lead mining & lead smelting work.

• From lead batteries, lead paints

• From the burning of waste oil, used as additive to petrol.

Effects:-

• High concentration of lead inhibits the production of hemoglobin in human beings.

• Causes anemia, kidney disfunctioning & permanent brain damage.

• The oxygen carrying capacity of the blood.

• Causes neurological and cardiovascular effects in children. Decrease growth and

reproductive rates in plants and animals.

Control methods:

• Replacement of conventional lead based products by lead free products.

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• Eliminate lead contamination in drinking water by process such as reverse osmosis,

distillation and filtration using carbon filters.

• By minimizing plant absorption of lead content in agriculture soil.

Secondary air pollutants:

These are the air pollutants that are not directly released into the atmosphere but forms

when primary pollutants reacting the atmosphere. Ex. Ozone , nitric acid , sulphuric acid.

Ozone: ozone is a triatomic oxygen molecule. Ozone forms a protective layer in the

stratosphere which absorbs potentially harmfull uv radiations from sun.

Formation:

In the stratosphere, ozone is formed from oxygen by the natural process. The oxygen absorbs uv

radiation below 240nm and photo dissociates into two reactive oxygen atoms.

O2 2O

The reactive or atomic oxygen combines with molecular oxygen producing ozone.

O + O2 O3

Ozone itself absorbs UV radiation in the range of 200-300nm release the oxygen ATOMS.

O3 O2+O

However, the released oxygen atom can recombine with oxygen again to form ozone. These

exists the dynamic equilibrium of formation of ozone.

Cause of ozone depletion:

The ozone layer is a natural protective layer of the earth, present in the lower portion of the

stratosphere. And majorly chlorofluorocarbons (CFC’s) which is a volatile organic compound

are the main cause for the ozone depletion.

Ozone depletion causes due to interactive between ozone and chlorine free radical of CFC’S.

CF2Cl2 CF2Cl + Cl•

Cl• catalyses the degradation of ozone.

Cl• + O3 ClO• + O2

ClO• + O Cl• + O2

The combined effect is

O3 O + O2

The free chlorine atoms again react with ozone and the process continues, resulting in depletion

of the ozone layer.

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Effects:

• Skin cancer, eye damage

• Immune systems damage.

• Accelerated aging of skin.

• Decrease in the crop yield.

• Cause the difficulty in breathing, chest pain, irritation in throat etc…

Control:

• Encourage growth of plants that produce O2, and stop deforestation.

• Control the release of ozone depleting substances.

• Use of alternatives for CFC’s such as HCFC & HFA.

Waste Management: Waste can take any form that is solid, liquid [or] gas.

Waste is any substance which is discarded after primary use.

Ex:- Municial solid waste, Hazardous waste, waste water, radioactive waste, etc…

Waste management is a collection, Transportation & disposal of waste.

[or]

Waste management is defined as “all the activities & Actions required to manage waste

from its collections to its final disposal.

It includes

• Collection

• Transport

• Treatment

• Disposal of waste

Simple Tips to reduce waste:-

• Use of reusable bags in stores.

• Reduce the use of paper plates & cups.

• Minimize use of plastic bags & Polystyrene foam.

• By donating unwanted, slightly used clothing, furniture & other household items to local

non-profit organizations.

• Purchase food in bulk [or] those which use less packaging.

• Purchase fruits that are pre-packaged in plastics.

1. Solid Waste Management:-

Solid waste is the unwanted [or] useless solid materials generated in residential,

industrial [or] commercial areas.

Ex: - Plastics, Glass, Metals, Dead animals, Hazardous waste, Construction

waste, etc…

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Solid waste management is a term that is used to refer to the process of collecting &

treating solid wastes.

Solid waste can be classified into different types. Depending on their source.

• Household waste as municipal waste.

• Industrial waste as hazardous waste.

• Biomedical waste as hospital/ infectious waste.

Sources, characteristics & Disposals of Solid waste:-

Sources:-

• Residential areas and homes

• Industries

• Commercial establishments

• Institutions

• Municipal services

• Manufacturing plants and sites

• Construction and demolition areas

• Agriculture

1) Residential areas: - Waste from these places includes food waste, plastic, paper, glass,

leather, arch, electronics batteries etc…

2) Industrial:-Industries produce solid waste in the form of housekeeping wastes, foodwaste,

packing waste,arhes,chemical water etc..

3) Institutions:-solid wastes obtained from these places include glass, rubber waste, plastics,

food wastes,wood,paper,metals etc..

4) Agriculture:-Agriculture solid wastes are spoiled food, pesticide container and other

hazardous materials

Characteristics:-

1) Physical Characteristics:-

• Density of waste

• Moisture content in wet waste

• Size distribution of materials

1) Density of waste:-It’s mass per unit volume called or density of waste. It is a critical

factor in the design of a solid waste Management system.

Example: the design of sanitary landfills, storage, types of collections and transport

vehicles etc...

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Chemical Characteristics:-

• lipids

• carbohydrates contents

• proteins

• natural fibers

• synthetic organic material

• non-carbohydrates

• heating value of waste

Disposal:-

Scientific landfills:-

• It is termed so because of its scientific design during constriction.

• The site selected for landfill should be for from dwelling of the ground water is for below

the surface.

• The landfill is given a betonies liner at the bottom and a layer of plastic material in order

to prevent any liquid material (leachate) to reach ground water and pollute.

• The landfill is filled daily with the waste and compacted using compactors and covered

with soil or alternative materials such as chipped wood.

• The leachates that are produced are collected through pipes and treated.

• The gases such as methane and co2come out due to microbial interaction.

• Methane is a flammable gas and is eithe r flared or can be collected for landfill gas

utilization.

• Once the landfill gets filled it is covered with fresh soil and could be used for growing

plants.

Composting:-

Due to lack of adequate space for landfills, biodegradable yard wastes are allowed to

composting process

Composting biodegrades organic waste along with leaves, grass trimmings, paper, wood into a

valuable organic fertilizer..

There are two most commonly used composting techniques

1) Home –composting:-

With a proper mixture of water, oxygen, carbon and nitrogen the microorganisms in the

waste are able to break down organic matter to produce compost

2) Commercial level vermi-composting:-

Vermi –compost is the product or process of organic material degradation using various

species of worms such as red wigglers, white worms and earthworms.

It is quick and most efficient composting method for heterogeneous mixture of waste

including fart decomposing vegetable or food waste.

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3) Recycling and reuse:-

Recycling of resources is the process of taking useful but discarded items for next use.

The plastic waste that is dumped can be recycled and reused.

Ex:-some percentage of plastics is mixed with asphalt for lying of roads.

A chemical waste can recover and reuse

Ex:-salts such as barium chloride and sodium sulphate are used in paint industry.

e-waste Management (Electronic waste):-

Electronic waste, popularly known as e-waste. It is defined as electronic products that

have become unwanted, on-working and have essentially reached the end of their useful life.

SOURCES:-

• Electronic devices such as TV’s, computer monitors, laptops and display devices.

• Telecommunication devices such as cellphones, calculators, audio and video devices,

printersscaneers, fax machines etc…..

• Electronic components such as sensors, alarms, sirens, security devices automobile

electronic devices.

• Kitchen equipments (coffee makers, microwave ovens)

• Laboratory equipments(hot plates,microscopes,microwave ovens)

Characteristics:

E-Waste is generally characterized by analyzing the components and composition of waste.

Hazardous components in e-waste:-

E-waste consists of a large number of components of various sizes and shapes, some of

which contain hazardous components that need to be removed for separate treatment.

Material composition of e-waste:-

❖ E-waste contains a mixture of various metals, particularly copper, aluminum and steel

etc...

DISPOSAL:-

Land filling:-This is the most common methodology of e-waste disposal.

❖ Soil is excavated and trenches are made for burying the e-waste in it.

❖ It is not an environmentally sound process for disposing off the e-waste as toxic

substances inside the soil and ground water.

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Inceration:-

This is a controlled way of disposing off the e-waste.

❖ It involves combustion of electronic waste at high temperature in specially designed

incinerators.

Recycling of e-waste: - It involves the re-reutilization of e-wastes with the help of the recycling

process.

This method involves dismantling of the electronic devices, separation of the parts having

hazardous substances like PCB’S and then recovery of the precious metals like copper ,gold and

lead can be done with the help of a e-waste recycler.

Reuse: - This is the most desirable e-waste recycling process where withmodifications the

mobile phones,computers,laptops,printers can be reused or given as second land product.

Biomedical waste:-

It is known as infectious waste or medical waste

It is defined as any waste produced during the diagnosis, treatment, and testing, medical

research Production of biological materials etc…

SOURCES:-

Waste generated from hospitals, clinics, labs, researchCentre, animalresearch,

bloodbanks, nursinghomes, home health care

The waste like discarded blood, unwanted microbiological cutlers and stocks, identifiable body

parts, human or animal tissue, used bandages and dressings discarded gloves, usedneedles,

scalpels etc…. are referred as biomedical waste.

Characteristics:

• It contains pathogenic microbes, radioactive substances, cytotoxic and heavy metals.

• It contains infectious waste materials

Ex:-lab cultures,tissues,blood, body parts etc...

• It consists of radioactive waste

Ex:-unused liquid radiotherapy

• It consists of chemical waste

Ex:-expired lab reagents

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DISPOSAL

Incineration: - it is a high temperature dry oxidation process that reduces organic and

combustible waste to inorganic, incombustible matter and results in a very significant reduction

of waste volume and weight.

This method is usually selected to treat waste that can not be recycled and reused.

Chemical disinfection: in this method certain chemicals are added to waste to kill or inactivate

the pathogens. Example: formaldehyde→ inactivates all micro organisms, bacteria, virus etc...

This treatment suitable for treating liquid waste such as blood, urine, stools.

Microwave irradiation:

Most microorganisms in bio medical waste or destroyed by the action of microwaves of a

frequency of 2450MHz and wavelength of 12 to 24cm.

Sanitary landfills:-

The use of landfill for bio-medical waste has to be treated as last option.

• It should not be dumped in open spaces as this leads to pollution problems, fires, higher

risks etc…

• Sanitary landfills are however safer, designed to have at least four advantages.

• Geological isolation of waste from the environment.

• appropriate engineering preparations before the site is ready to accept waste

• Staff prevent on site to control operations.

• Organized deposit and daily coverage of waste.

WATER CHEMISTRY

Introduction:-

Water is the one of the most basic and essential component to all life. It covers ¾th of the

earth’s surface. Water is the second most important substance required to sustain human, animal

and plant lives. Water is used for both domestic and industrial purposes such as drinking and

washing in the manufacture of paper, textiles, sugar and in steam power plants.

Source of water:-

The source of water is classified as Surface water & underground water.

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1. Surface Water

a. Rain water: - Is supposed to be the purest from water. However, it dissolves

considerable amount of gases and suspended solid particles from the atmosphere

during its downward journey.

b. River water: - It contains dissolved minerals of the soils such as Chlorides,

Sulphates, and bicarbonates of sodium, calcium, magnesium and iron. It also contains

organic matter, derived from the decomposition of plants & small particles of sand &

soil in suspension.

c. Lake water: - It contains less dissolved minerals, but a quite high quantity of organic

matter.

d. Sea water: - Is the most impure from of natural water. It contains 3.5% dissolved

salts out of which 2.6% is NaCl. Other salts are sulphates, bicarbonates, bromides of

potassium, magnesium & calcium.

2. Underground water

Spring & Well water is forming the underground water sources. In general, clearer in

appearance due to the filtering action of the soil, but contains more of the dissolved salts.

Impurities of water:-

Impurities in natural water broadly classified in to four categories.

1. Dissolved Impurities.

2. Suspended Impurities.

3. Dissolved Gases.

4. Organic matter.

1. Dissolved Impurities:-

A dissolved impurity mainly consists of bicarbonates, chlorides and sulphates of calcium,

magnesium and sodium. In addition, small amounts of nitrates, nitrites, silicates, ammonium and

ferrous salts are also present.

2. Suspended Matter:-

The Suspended matter may be inorganic (or) organic in nature. The inorganic materials

include small particles of sand, Clay, silica, hydroxides of Iron. Some of these have large particle

size and therefore settle down readily. Others are fine particles and colloidal in nature. These do

not settle down easily.

The organic suspensions are decaying vegetable matter are due to micro-organisms.

These consists mainly bacteria and other micro-organisms like algae and fungi etc.

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3. Dissolved gases:-

Most waters contain dissolved gases such as oxygen, carbon-di-oxide, sulphur-di-oxide,

ammonia and oxides of nitrogen all of which are derived from atmosphere.

4. Organic matter:-

Organic compounds are derived from the decay of vegetable and animal matter including

bacteria. Water also gets contaminated with sewage and human excreta.

Ex: - Pathogenic bacteria such as Typhoid Bacillus.

Boiler Feed Water:-

Water is mainly used in boilers for the generation of steam for industries and power houses.

(or)

The water used to generate steam in boiler is called Boiler fed water.

The boiler feed water must be pure and should have specific characteristics.

Characteristics of Boiler Feed Water:-

• Its hardness should be 0.2ppm.

• Its caustic alkalinity [due to OH-] should lie in between 0.15 and 0.45PPM.

• Its soda alkalinity due to Na2CO3 should be 0.456 to 1 PPM.

• Its PH is 7.5 to 10.

If excess of impurities present in boiler feed water, they lead to the formation of Scales,

Sludges, Priming, Foaming, Corrosion and Caustic embrittlement.

Boiler Troubles:- The major boiler troubles are

• Scale and Sludge formation

• Priming and Foaming

• Boiler Corrosion

1. Scale and Sludge Formation:-

Scale Formation:-

The precipitate so formed is in the form of hard deposit which is coated to the walls of

the boiler is called scale.

The scales are formed by the impurities in water such as MgCl2, Mg (HCO3)2, CaSO4 and

Silica. Removal of scale is very difficult.

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Causes for Scale Formation:-

• Decomposition of Bicarbonates:-

If bicarbonates are present as impurities, they precipitate as their highly insoluble carbonates.

Mg (HCO3)2 MgCO3 + CO2 + H2O

The scale formed due to calcium carbonate is soft, and is the main cause of scale formation in

low pressure boilers.

Ca (HCO3)2 CaCO3 + CO 2+ H2O

In high pressure boilers, CaCO3 is soluble due to the formation of Ca (OH) 2.

CaCO3(s) + H2O (g) Ca (OH) 2 (aq) + CO2 (g)

• Solubility of the calcium sulphate also decreases along with increase in boiler

temperature. Thus it also gets precipitated out in the form of scales.

• Presence of Silica:-

Silica reacts with calcium and magnesium present in water to from silicates of calcium

and magnesium. These silicates from hard and glassy scale on inner surface of boiler.

• Hydrolysis of salts of Magnesium:-

Magnesium salts get hydrolyzed at high temperature forming, a soft scale

magnesium hydroxide precipitate.

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

Disadvantages of Scale Formation:-

1. Wastage of Fuel: - Scales have a poor conductor of heat, so the rate of heat transfer from

boiler to water is greatly reduced.

2. Reduces boiler efficiency: - Decomposition of scales in the valves and condensers of the

boiler, choke them partially.

3. Increase in cleaning expenses: - Scales must be removed regularly and this cleaning

process is very much expensive.

4. Lowering of boiler safety: - The overheating of the boiler tube makes the boiler material

softer and weaker.

5. Danger of explosion: - The scale formation also leads to uneven expansion of boiler

material.

Removal of Scales:-

• Loose scales can be removed by using wooden scraper (or) Piece.

• Brittle scales can be removed by giving thermal shocks.

• By frequent blow-down operation, if the scales are loosely adhering.

• Chemical treatment with 5-10% HCl for carbonates and EDTA for Ca/Mg.

Sludge Formation:-

The precipitate formed is a loose, non-adherent and suspended precipitate in the boiler

feed water then it is called Sludge.

The impurities which have more solubility in hot water than in cold water from Sludge.

The impurities of water which causes sludge formation are MgCO3, MgSO4, and CaCl2 etc…….

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Disadvantages of Sludge Formation:-

• Sludge is a poor conductor of heat. Therefore it requires more heating of boiler to

produce steam which results into wastage of fuel.

• Sludges reduce the efficiency of the boiler.

• Sludges need to be removed regularly and this cleaning process is expensive.

Boiler corrosion:-

It is decay (or) disintegration of boiler material either due to chemical (or)

electrochemical reaction with its environment is called boiler corrosion.

(OR)

The decay of boiler material due to presence of impurities in boiler feed water is called

boiler corrosion.

This process reduces the life of boiler and is caused by dissolved oxygen, dissolved

carbon dioxide and some dissolved salts in boiler feed water.

Corrosion in boilers is due to the following reasons:-

1. Corrosion due to Dissolved oxygen:-

When water contain dissolved oxygen is heated in the boiler, the free gas is evolved

under high pressure of the boiler and attacks the boiler materials and forms the rust.

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

4Fe (OH) 2 + O2 2[Fe2O3.2H2O]

Rust

2. Corrosion due to Dissolved Carbon-di-oxide:-

The carbon-di-oxide is present in the boiler water either from air (or) due to

decomposition of salts at high temperature.

Ca (HCO3)2 CaCO3 + CO2 + H2O

Mg (HCO3)2 Mg (OH) 2 + 2CO2

So formed CO2 will dissolve in water and produce carbonic acid. The carbonic acid is

slightly acidic and corrosive in nature.

H2O + CO2 H2CO3.

1. Corrosion due to MgCl2:-

Due to the pressure of salt like MgCl2 in boiler feed water, the PH value drops below

8.5, because of the following reaction.

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

The acid so formed will attack the boiler parts and causes corrosion.

Fe + 2HCl FeCl2 + H2

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

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Controlling of Boiler Corrosion:-

Boiler corrosion can be controlled by reducing the quantities of O2, CO2 and any acid

from the feed water.

1. Removal of Oxygen:-

Dissolved oxygen can be removed by treating boiler feed water with sodium sulphite

(OR) with hydrazine (OR) sodium sulphide.

2Na2SO3 + O2 2Na2SO4

N2H4 +O2 N2 + 2H2O

Na2S + 2O2 Na2SO4

2. Removal of CO2 :-

• Lime stone removes carbon-di-oxide.

CaCO3 + H2O + CO2 Ca (HCO3)2

• CO2 can be removed by adding calculated amount of NH4OH [Ammonium

hydroxide]

2NH4OH + CO2 (NH4)2CO3 + H2O

3. Finally acidic impurities if there any can be removed by treating with alkaline agents like

ammonium hydroxide

Chemical Oxygen Demand [COD]:-

COD is also a measure of level of water pollution. BOD value accounts for only

biologically oxidizable impurities, however, COD value accounts for both biologically

oxidizable and non-oxidizable organic matter present in water sample.

COD is defined as “The amount of oxygen required to oxidize both biological and non-

biological oxidizable organic and inorganic impurities present in 1dm3 of waste water using

strong oxidizing agents like acidified K2Cr2O7”.

It is expressed in mg of O2 per liter.

Determination of COD of a waste water sample:-

Principle:-

The principle involved in the method is to treat the given water sample with K2Cr2O7

solution for the oxidation of impurities in acidic medium using Ag2So4 as catalyst & HgSo4 [to

prevent chloride interference]. The unreacted K2Cr2O7 was estimated by titrating against

standard ferrous ammonium sulphate [FAS] using ferroin indicator.

Ex: - 3CH2O + 16H+ + 2Cr6+ 4Cr3+ + 3Co2 + 11H2O

To find out this a blank titration without waste water sample is carried out.

Engg. Chemistry


Procedure:-

➢ Pipette out known volume of waste water sample and add 25cm3 of K2Cr2O7 solution into

a 250cm3 conical flask.

➢ Add one test tube full of 1:1 sulphuric acid containing silver sulphate (AgSO4) and

mercuric sulphate (HgSO4).

➢ Reflux the mixture for half-an-hour and cool. Add 2drops of Ferroin indicator.

➢ Titrate the above mixture against FAS solution till colour changes from blue green to

reddish brown.

Let the volume of FAS consumed be ‘V1’cm3.

➢ Carry out blank titration by taking 25ml of distilled water and repeat the procedure

without sample in the same way, the volume of FAS consumed be ‘V2’cm3.

Calculation:-

COD of waste water sample = 𝑵 𝑿 (𝑽𝟐−𝑽𝟏) 𝑿 𝟖𝟎𝟎𝟎

𝑽𝑾𝒂𝒕𝒆𝒓 𝑺𝒂𝒎𝒑𝒍𝒆 mg of O2/lt.

Where N= Normality of FAS solution.

V1= Volume of FAS consumed for sample titration.

V2= Volume of FAS consumed for Blank titration.

Numerical on COD:-

1. In a COD test, 28.1Cm3 and 14.0Cm3 of 0.05N FAS solution were required for blank and

sample titration respectively. The volume of test sample used is 25Cm3. Calculate the

COD of the sample solution.

Solution:-

COD of waste water sample = 𝑁 𝑋 (𝑉2−𝑉1) 𝑋 8000

𝑉𝑊𝑎𝑡𝑒𝑟 𝑆𝑎𝑚𝑝𝑙𝑒 mg of O2/dm3.

= 0.05 × (28.1−14.0) ×8000

25 = 225.6 mg/dm3

2. 25ml of waste water was mixed with 10ml of K2Cr2O7 acidified required 15.2ml of 0.3N

FAS. In a blank titration 10ml of K2Cr2O7 acidified 19.4ml of same 0.3N FAS. Calculate

COD of waste water.

ANS:-403.2 mg of oxygen/dm3

3. 25Cm3 of sewage water was refluxed with 10Cm3of 0.25N K2Cr2O7 in con.H2SO4

medium. The unreacted K2Cr2O7 needed 6.1 Cm3. Of 0.1N FAS. 10Cm3 of 0.25N

K2Cr2O7 when titrated under same condition required 28.2Cm3 of 0.1N FAS. Calculate

the COD.

4. 25 Cm3 of an effluent sample was reacted with 15ml of 0.5N K2Cr2O7 solution & after

reaction; the unreacted K2Cr2O7 required 20ml of 0.1N FAS for reaction. Under similar

condition, 15ml if 0.5N K2Cr2O7 solution mixed with 25.0 cm3 of distilled water required

30ml of 0.1N FAS. Calculate COD of the effluent sample. ANS: - 320 mg of oxygen/dm3.

Engg. Chemistry


5. 25 cm3 of an effluent requires 8.3cm3 of 0.01M acidified K2Cr2O7 for complete oxidation.

Calculate the COD of the effluent sample.[June/July-2016]

Solution:-

(i). Evaluate the oxygen equivalent:

1000 cm3 of 1M (or) 6N solution of K2Cr2O7= 48 g of oxygen.

8.3 cm3 of 0.001M solution of K2Cr2O7 = 48 ×0.01 ×8.3

1000

= 0.003984 g of O2

= 3.984 mg of O2.

(ii) Calculate the COD value:-

25 cm3 of effluent = 3.98 mg of O2/dm3

1000 cm3 of effluent = 3.98 ×1000

25

= 159.2 mg of O2/dm3.

6. In a COD determination 25mlof an industrial effluent required 12.5 ml of 0.015M

K2Cr2O7 for complete oxidation. Calculate COD of the effluent sample.

(i). Evaluate the oxygen equivalent:

1000 cm3 of 1M (or) 6N solution of K2Cr2O7= 48 g of oxygen.

12.5 cm3 of 0.0015M solution of K2Cr2O7 = 48 ×0.015 ×12.5

1000

= 0.009 g of O2

= 9mg of O2.

(ii) Calculate the COD value:-

25 cm3 of effluent = 9 mg of O2/dm3

1000 cm3 of effluent = 9 ×1000

25

= 360 mg of O2/dm3.

7. In a COD determination 25mlof an industrial effluent required 8.5 ml of 0.001M K2Cr2O7

for complete oxidation. Calculate COD of the effluent sample.

Biological Oxygen Demand:-

BOD is defined as “The amount of oxygen required for the biologically oxidation of

oxidizable impurities present in 1dm3 of waste water under aerobic conditions for a period of

5days at 20°c”.

It is expressed in mg/dm3 of oxygen.

Sewage Treatment:-

Polluted water is commonly referred to as Sewage.

Sewage is the liquid waste from domestic use like kitchen, toilets and laboratories.

Sewage treatment is the process of removing contaminants from sewage.

The treatment of sewage is carried out in three stages.

1. Primary Treatment.

2. Secondary Treatment.

3. Tertiary Treatment..

Engg. Chemistry


1. Primary Treatment:-

In this stage suspended solid impurities and floating materials present in polluted

water are removed by different ways.

• Screening and maceration:-

Maceration is where the large solids are cut into small particles through the use of

rotating knife edges. Then the liquid is passed through fixed (or) rotating screens to

remove floating materials such as rags and suspended small particles.

• Silt & Grit Removal:-

In this step, sewage is passed through channels in a grit chamber slowly. Slit &

grit particles [sand, broken glass , bone chips] being heavy settle down at the bottom.

• Sedimentation:-

The fine solid particles are removed by using coagulating agents like alum, FeSO4

etc.. These compounds produce gelatinous precipitate of their metal hydroxides, which

absorb fine particles and settle at the bottom, then removed by filtration.

FeSO4 + H2O Fe (OH) 2 + H2SO4

Al2SO4 + 3Ca (HCO3)2 2Al (OH) 3 + 3CaSO4 + 6CO2.

2. Secondary Treatment:-

Secondary treatment involves the removal of biologically oxidizable impurities in sewage.

Ex:- Activated Sludge process.

Activated Sludge Process:-

In this method waste water sample after primary treatment is mixed with activated sludge

[water sample containing higher concentration of microorganisms] are taken into large tank. Air

is passed into the tank maintain aerobic conditions. Under aerobic conditions microorganisms

oxidize biologically oxidizable impurities into CO2.

After this process, sewage is sent to sedimentary tank where sludge is deposited & water

free from organic matter is brawn off. The sludge is sent back to aeration tank & treated with

new sewage.

NH2CONH2 + O2 CO2 + 2NH3

Org.matter.

Biologically oxidizable impurities + O2 CO2 + H2O.

Engg. Chemistry


3. Tertiary Treatment:-

It involves the removal of dangerous chemicals present in sewage.

Treatment in this stage depends on the type of impurities present in it.

a. Phosphate is removed by treating water with lime [Calcium Hydroxide].

Ca (OH) 2 + PO43- Ca (PO4)2

b. Toxic metals like Cd2+ ,Pb2+, AS2+, Hg2+, Zn2+ can be removed by passing H2S gas

through water.

Mn+ + H2S MS

c. The suspended fine particles are removed by sedimentation in the presence of coagulating

agents such as alum, ferrous sulphate etc…

Al2 (SO4)3 + 6H2O 2Al (OH) 3 + H2SO4

FeSO4 + 2H2O Fe (OH) 2 + H2SO4

d. Organic compounds like pesticides [DDT] are removed by adsorption on activated

charcoal.

e. The last trace of suspended matter is removed by filtering the water through sand filter

beds.

f. Chlorination is carried out to kill pathogenic bacteria.

It is done by adding either bleaching powder (or) by blowing chlorine gas.

Cl2 + H2O HOCl

Hypochlorous acid.

HOCl formed by the above reaction kills all pathogenic bacteria present in water.

Diseases causing bacteria + HOCl Bacteria’s are killed...

Sedi

ment

ary

Tank

Sludge

Recycle Disposal

Engg. Chemistry


Chemical Analysis of Water:-

Determination of Sulphate by Gravimetric Method:-

Principle:-

The method involves Precipitation by adding dilute BaCl2 to a known volume of water

sample to precipitate as BaSO4. Precipitate of BaSO4 is separated by filtration, dried & weighed.

The amount of sulphate is calculated & expressed as mg SO4 in one liter of the water sample.

Procedure:-

• A known volume of water sample is taken in a beaker with a glass rod.

• The water sample is acidified with sulphate free HCl & then heated on a hot plate.

• Add 10% BaCl2 solution dropwise with continuous stirring till all the sulphate is

precipitated as BaSO4.

• The mixture is placed on a water bath for 30min, for completion of precipitation & settles

faster.

• The mixture is carefully filtered through a whatman 40 filter paper.

• Transfer the filter paper containing BaSO4 precipitate into a previously dried & weighed

silica crucible (W1) & burn it in a electrical burner.

• The crucible along with the precipitate is cooled & note down the weight of crucible

(W2).

• Calculate mass of BaSO4 precipitate from the difference in weights of the crucible before

& after burnt.

Calculation: - The amount of sulphate in the given volume of a water sample is calculated as

233.3 mg of BaSO4 = 96 mg of SO42-

W mg of BaSO4 = 𝑊 𝑋 96

233.3 mg of SO4

2-

V ml of water = 𝑊 𝑋 96

233.3 mg of SO4

2-

1000ml of water = 𝑾 𝑿 𝟗𝟔 𝑿 𝟏𝟎𝟎𝟎

𝟐𝟑𝟑.𝟑 𝑿 𝑽 mg of SO4

2-

Determination of Fluoride by SPADNS method using Colorimetry:-

Principle:-

Under acidic conditions, fluoride ions react with Zirconyl-SPADNS reagent & the

intensity of the colour of the reagent decreases. The decrease in intensity is related to the

concentration of fluoride ions. By measuring the absorbance of the sample after treating with the

reagent complex, the amount of fluoride present in the sample of water is determined.

Engg. Chemistry


Procedure:-

• Prepare a blank solution by adding 10ml acid Zirconyl-SPADNS reagent to 100ml

distilled water, use this solution to set zero in the colorimeter at 570nm.

• Prepare a series of standard solution of NaF in the concentration range of 0-0.2 mg/lt.

• Add a drop of NaASO2 [sodium arsenite] solution to remove any residual chlorine.

• Add 10ml of acid Zirconyl-SPADNS reagent to each standard solution.

• Dilute up to the mark & mixwell, measure absorbance at 570nm using a colorimeter.

• Take a known volume of water sample & repat steps 3,4, & 5.

• Draw a calibration cruve by plotting the graph of concentration of fluoride ion against

absorbance.

• Calculate the concentration of fluoride ion in the sample using calibration curve.

Softening of Water:-

The process of removal of calcium, magnesium, iron salts and other metallic ions from

water is called Softening of water.

Three important methods used for water softening are,

➢ Cold and hot lime [soda process].

➢ Zeolite process.

➢ Ion-exchange process.

Ion Exchange process:-

“Ion-exchange is the process of softening of water by exchanging the harmful ions of

water with harmless ions from an ion-exchange resin”.

An ion-exchange resin is a cross-linked organic polymer network having some ionisable

groups. [Functional group].

Depending upon functional groups attached to resins they are classified into

➢ Cation Exchange Resin.

➢ Anion Exchange Resin.

a. Cation Exchange Resin:-

Resins have –SO3H, -COOH, and (Or) –OH [Phenolic] group as the functional groups

are called Cation-Exchange Resins

These resins exchange the cationic portion of minerals by their hydrogen.

These are generally represented as RH+.

Engg. Chemistry


b. Anion-Exchange Resins:-

Resins have –NH2, -NHCH3, -N(CH3)2, groups with their hydroxide salts are called

anion-exchange resins.

These resins exchange the anionic portion of minerals by their OH- ions.

These are generally represented as ROH-.

Softening of Water by Ion-Exchange method:-

In this process Cation and Anion exchange resins are packed in separate columns.

Water is first passed through a tank having cation exchanger which absorbs all the cations

present in water and leaves behind the hydrogen ions. [H+].

2RH+ + Mg2+ R2Mg2+ + 2H+

2RH+ + Ca2+ R2Ca2+ + 2H+

The cation free water is now passed through a anion exchanger which absorbs all the

anions present in water and leaves behind OH- ions.

ROH- + Cl- RCl- + OH-

2ROH- + SO2-4 R2SO2

-4 + OH-

Now, H+ ions formed at cation exchanger resin and OH- ions formed at anion exchange

resin will combine to form water.

H+ + OH- H2O

Thus water coming out of two resins is ions free and called as ion-exchanged (or)

dematerialized water.

Anion Exchange Resin Cation Exchange Resin

Hard Water Soft Water

Engg. Chemistry


Advantages:-

• The ion-exchange apparatus, once set up, is easy to operate and control.

• Both acidic and alkaline water can be softened.

• Water of very low hardness is produced.

• Water produced by this method is used as boiler feed water.

Disadvantages:-

• Equipment and process is costly.

• Turbid water needs to be filtered first before softening.

Desalination of Sea Water:-

The process of partial (or) complete demineralization (or) removal of dissolved salts from

Sea water is called Desalination if water.

The methods are used to desalination of water are,

a. Reverse Osmosis.

b. Electrodialysis.

c. Flash evaporation.

Reverse Osmosis:-

The movement of solution molecules through semipermeable membrane from higher

concentration to lower concentration is called Reverse Osmosis.

Principle:-

It involves separation of salt from sea water through a semipermeable membrane. The

movement of water takes place from higher to lower concentration under the influence of applied

pressure through a semipermeable membrane.

Process:-

A typical reverse osmosis chamber consists of inlet through which hard water is passed at

25-30 atmospheric pressure. A series of tubes made up of porous material is lined on inside with

extremely thin film of cellulose acetate semipermeable membrane only water molecules can pass

through the membrane and salt will be retained on the membrane. The flow of water is

proportional to applied pressure which in turn depends on the characteristics of the film.

Concentrated brine & fresh water are withdrawn through their respective outlets.

Engg. Chemistry


Applications:-

• It is economical, simple and continuous.

• The process needs extremely low energy.

• It has long life and membrane is easily replaceable.

Disadvantages:-

• It cannot be used for large scale production.

• Variation of pressure may results in rupture of membrane.

Most Probable Questions:-

Environmental Pollution:-

1. What are the Sources, Effects & Controlling Methods of Carbon-monoxide Pollutant?

2. What are the Sources, Effects & Controlling Methods of Nitrogen oxide Pollutant?

3. What are the Sources, Effects & Controlling Methods of sulphur oxide Pollutant?

4. What are the Sources, Effects & Controlling Methods of Hydrocarbon Pollutant?

5. What are the Sources, Effects & Controlling Methods of Particulate Matter?

6. Explain the Mechanism of Formation of Photochemical Smog.

7. What are the Sources, Effects & Controlling Methods of Mercury Pollutant?

8. What are the Sources, Effects & Controlling Methods of Lead Pollutant?

9. What are the causes, effects and disposal methods of Solid waste?

10. What are the causes, effects and disposal methods of e-waste?

11. What are the causes, effects and disposal methods of biomedical waste?

Water Chemistry: -

1. Define Boiler feed water. Explain Formation of Scale & Sludge.

2. Explain Boiler Corrosion due to dissolved O2, CO2 & dissolved salts like MgCl2.

3. Define COD & BOD. Explain determination of COD.

4. Explain the Activated Sludge treatment of sewage water.

5. Explain determination of Sulphate by gravimetrically.

6. Explain determination of Fluoride by SPADNS method using colorimetry.

7. Define Softening of water. Explain Softening of water by Ion-Exchange method.

8. Define Desalination of water. Explain Desalination of water by Reverse Osmosis Process.

9. Numerical on COD.

Sea Water

Sea Water

Out let

Fresh Water

Out let

SVCE, Engg. Chemistry, Module-05 Page 1

MODULE – V

MODULE-V: Instrumental methods of analysis and Nanomaterials :

Instrumental methods of analysis: Theory, Instrumentation and applications of Colorimetry,

Flame Photometry, Atomic Absorption Spectroscopy, Potentiometry, Conductometry (Strong

acid with a strong base, weak acid with a strong base, mixture of strong acid and a weak acid

with a strong base).

Nanomaterials: Introduction, size dependent properties (Surface area, Electrical, Optical,

Catalytic and Thermal properties). Synthesis of nanomaterials: Top down and bottom up

approaches, Synthesis by Sol-gel, precipitation and chemical vapour deposition, Nanoscale

materials: Fullerenes, Carbon nanotubes and graphenes – properties and applications.

(RBT Levels: L1 & L2)

Instrumental Method of Analysis

Instrumental methods use a simple [or] advanced instrument to measure physical quantities of

the analyte by relating the concentration with light absorption, fluorescence, conductivity [or]

potential.

Instrumental method of analysis can be classified into two types.

1. Electrical Method: - it involves the measurement of current, voltage [or] resistance

in relation to the concentration of a certain species in solution.

Ex: - Potentiometric, Conductometric methods, etc…

2. Optical Method: - the optical methods are based on how the sample acts towards the

electromagnetic radiation. Ex:- Colorimetry

Advantages:-

• The method is much faster than the chemical methods.

• It requires small quantities of the analyte.

• The analysis can be conducted in a very short time.

• They give accurate results.

Disadvantages: -

• The instruments are expensive.

• The concentration range is limited.

• Specialized training is needed for the operation.


Colorimetry

Theory:- Chemical analysis through measurement of absorption of light of a particular

wavelength is known as Colourimetry.

Beer’s law:-

The intensity of a beam of monochromatic light decreases exponentially as the concentration of

the absorbing species increase arithmetically.

Beer – Lambert’s Law:

When a monochromatic (light having only one colour) radiation of intensity ‘I’ is passed

through a solution of a sample under investigation taken in a cell of thickness ‘t’ a portion of

radiation is absorbed (Ia), a portion is reflected (Ir) and the remainder is transmitted (It) then,

In the case of transparent medium the intensity due to reflection is negligible,

Therefore, I = Ia + It

Lambert’s Law:

It states that “when monochromatic light passes through a transparent medium, the rate of

decrease in intensity with the thickness of the medium is proportional to the intensity of the light

mathematically it can be expressed as

It = I0 e-kt

This eqn shows the exponential decrease in intensity of transmitted light with the increase in

thickness of the medium

Instrumentation

The essential parts of colorimeter are

1. Light Source-Mercury lamp.

2. Filter- To filter undesired radiations , it allows radiations of a definite wave length range

to pass through it and reach the sample

3. Kuwatte- To take sample

4. Photocell- To receive the transmitted light.

5. Recorder – to record the absorbance in nm.

I = Ia + Ir + It


Colorimetric determination of copper

When cupric ions are treated with ammonia, it gives deep blue coloured cupra ammonium

compound. The absorbance is measured at 620 nm(λmax). Since the complex shows the

absorbance maximum at this straight line will be obtained. From this unknown solution

concentration can be obtain by

measuring the absorbance of

unknown solution.

Procedure:-

• Take known amount of standard solution 2, 4, 6, 8 and 10 cm3 in deferent 25 cm3

standard flasks.

• add 2.5 ml of ammonia into each of these flask and make up to the mark with distilled

water and mix well for uniform concentration.

• After measure the absorbance of all solutions against blank at 620 nm using a photo

electric colorimeter. Note down the optical density of all solutions and tabulate the

readings.

• Draw a calibration curve by plotting absorbance against concentration of copper or

volume of copper of solution taken.

• find out the unknown volume of copper sulphate solution given and calculate the amount

of copper present in it.

Cu2+

present in test solution = V

a

50

Applications:

• In quantitative analysis: large number of metal ions, anions and cations compounds can be determined by in this method

• Photometric Titration i.e. equivalence point can also be determined

• Determination of the composition of colored complex Advantages:

• Can be determine the concentration of the colored solution

A

Ab

sorb

an

ce

Concentration of Copper


• It is very simple method

• Colorimeter gives most accurate value

• Used for lower concentration

Potentiometry Theory

Determination of concentration of ionic solution by measuring the emf (electromotive force) is

reffered to as potentiometry.

Potentiometric methods include two types of

measurement a) direct measurement of an electrode

potential from which the concentration of an active ion

may be found.

b) changes in the emf of an electrolytic cell brought

about by an addition of a titrant.

The potential of an electrode is given by Nernst eqn,

E = E0 + 0.0591 log [ M n+]

n

E0 Standard electrode potential, Electro potential depends on the concentration of the ion.

(E0 – It is the electrode potential of a metal in contact with its ions in 1 molar)

Instrumentation:-

The Potentiometer consists of a reference electrode, an indicator electrode and potential

measuring device. The indicator electrode response rapidly to the changes in the concentration of

analysis i.e the solution understudy. This is made up of platinum, indium, gold and other noble

gases. The potential of the indicator electrode is measured using an electrode known as reference

electrode. It is made up of mercury, mercury oxide or silver-silver chloride.

Procedure:-

A known volume of analyte is taken and its potential is determined. The titrant is added in

increment of 1ml and the emf is measured each time at equivalence point, the emf tends to

increase rapidly.

At this point readings are more taken frequently at the intervals of 0.1cm3 to find the

equivalence point plot a graph of ΔE/ΔV Vs volume of the titrant added.

Applications

a) Acid-base titration

It is known that the neutralization of acid and bases is always accompanied by the changes in the

concentration of H+ and OH- ions, Hydrogen electrode is measured in this titration


A known volume of an acid (HCl) to be titrated against base NaOH. An electrode

potential depends on hydrogen ion concentration is analyte emf of the cell ( H2 electrode) is

given by

E = E0 + 0.0591 pH

When the titration proceeds H+ ion concentration goes on decreasing this results PH goes on

increasing, the changes in electrode potential (or) emf of the cell is proportional to the change in

PH during titration.

Therefore emf of the cell increases, initially the emf changes slowly and then rapidly as

the neutralization point approach. After equivalence point, further addition of NaoH produces the

little change in H+ concentration and hence there is no significant change in emf

For finding endpoint plot a graph of change in emf again the volume of titrant . A more sensitive

and satisfactory method of finding the endpoint to plot a graph of ΔE/ΔV against V.

Determine the end point by plotting E

against the volume as shown in the figure.

V

b) Oxidation Reduction reactions; Estimation of amount FAS in FAS solution

FAS vs. K2Cr2O7

Redox reaction can be followed by an inert indicator electrode (i.e Pt).

The Electrode potential is proportional to log of the concentration ratio of the oxidation states of

reactant

Oxidized form + n electrons → Reduced form

Electrode potential at 25 oC is given by

• These titration involves the transfer of electrodes from the substance being oxidized to the

substance being reduced

• In this titration the potential of the two systems are important i.e the one oxidized and one

reduced, the change of potential end point is maximum generally the oxidizing agent is

placed in burette.

Eg: Iron (II) with K2Cr2 O7

Fe2+ Fe3+ + 1e

K2Cr2O7 + 14H+ 6e 2 Cr3+ + 7 H2O

E = E0 +0.0591 log 10 (Oxidized form)

n (Reduced form)


Applications:

1. Coloured solution can also be titrated. 2. Acid-base titration can also be done in this method.

3. In this method Oxidation-reduction titrations can also be carried out.

4. Precipitation reactions can also be carried out potentiometrically.

Conductometry: Conductometry is an electrochemical method of analysis based on measuring the resistance of an

electrolytic solution.

Definition of conductance: Reciprocal of resistance is called conductance i.e. C=1/R

It is expressed in ohm-1 or Mho.

Theory: Ohm’s law states that the current (I) in amperes flowing in a conductometer is directly

proportional to the applied emf. E (vol) and inversely

proportional to the resistance, R (ohm) of the conductor.

I = E

R

The reciprocal of resistance is called the conductance.

The theory involved in conductometric titration is that

conductance of an electrolytic solution depends upon the

nature, number, and mobility of the ions in solution. Larger

the concentration of fast mobile ions higher will be the

conductance and Vice versa.

Specific Conductance:-

It is defined as “the conductance of the solution present b/w two parallel electrodes of

cm2 area of cross section & 1cm apart”.

Instrumentation:

Conductometer consists of two platinum electrodes and a conductance measuring

device. The two electrodes have unit area of cross section and are placed unit distance apart. The

assembly responds rapidly to the changes in the concentration of the analyte.


Applications:

1. Strong acid Vs strong base: (HCL V/S NaOH)

HCl(H+ + Cl-) + NaOH (Na+ + OH-) NaCl (Na+ + Cl-) + H2O In the case of strong acid and strong base, the conductance 1st falls, due to the replacement of

highly mobile H+ ion by less mobile Na+ ions. After the equivalence point, the conductance

rapidly rises with further addition of strong base and is due to increase in the concentration of the

OH- ions.

2. Mixture of strong acid and a weak acid Vs strong base (HCl & CH3COOH V/S

NaOH)

In aqueous solution of a mixture of acids, one can expect preferentially the neutralization of a

strong acid with a strong base like NaOH and the completely ionized H+ ions of the strong acid

reacts with OH- ions of the strong base giving unionized water. When every H+ ions of the strong

acid is neutralized; the first end point is obtained.

The weak acid does not get neutralized initially because of the well-known common-ion

effect. In the presence of excess of H+ ions, the ionization of the weak acid is suppressed and

hence, the weak acid does not provide H+ ions for neutralization during the first phase of

titration.

A weak acid like CH3COOH, ionizes gradually after the first end point and the available H+

ions are neutralized, giving the second end point.

3. Weak acid Vs strong base (CH3COOH V/S NaOH)

Weak acid partially dissociated in aqueous solution the conductance of the of the acid will be

initially low due to poor dissociation. When a strong base is added to the acid, the salt formed is

highly ionized and conductance increases on complete neutralization of the acid, further addition

of base lead to an increase in the number of more OH- ion and hence conductance increase

sharply.

CH3COOH (H+

+ CH3COO-)+ NaOH (Na

+ + OH

-) ------- CH3COONa (Na

++CH3COO

-) + H2O


Advantages:

1. Mixtures of acids can be titrated

2. Accurate in dilute solutions

3. Very weak acids which can’t be titrated potentiometrically but it can be titrated

conductometrically

Advantages of Instrumental method of Analysis over Chemical analysis:

1. Chemical methods are time consuming procedures. It requires large time for analysis but

instrumental methods are much faster.

2. Chemical methods require large amount of the analyte (sample) but instrumental method

requires very small amount of sample like ppm level.

3. They are wide applications in industries.

4. The analytical process can be automated.

Disadvantages:

1. The instruments are expensive

2. An initial or continuous calibration is required using a sample of material of known

composition

3. The concentration range is limited

4. Specialized training is needed for the operation of certain sophisticated instruments

Flame photometry Principle: The Flame photometry is emission of characteristic radiation by an element and the correlation of the emission intensity with the concentration of the element.

MX(aq) M+X

- MX(s) MX(g) M(g)

+ + X(g)-

hv

M* Excited state

When a solution containing a compound of the metal to be investigated is aspirated into

a flame, the following processes occur.

i) Solvent evaporates leaving behind a solid residue.

ii) Vaporization of the solid coupled with dissociation into its constituent atoms, which are

initially in the ground state.

iii) Some gaseous atoms get excited by the thermal energy of the flame to higher energy levels.

The excited atoms, which are unstable quickly, emit photons and return to lower energy

state i.e. ground state. Flame photometry involves the measurement of emitted radiation.

The relationship between the ground state and excited state populations is given by

the Boltzmann equation:

N1/N0= (g

1/g

0) eE/kT


N1 = Number of atoms in the excited state; N0 = Number of atoms in the ground state, g1/g

0 =

ratio of statistical weights for ground and excited states; E = Energy of excitation = h k is

the Boltzmann constant; T = Absolute Temperature

From the above equation, it is evident that the ratio N1/N0 is dependent upon both the

excitation energy E and the temperature T. An increase in temperature and a decrease in E will

both result in a higher value for the ratio N1/N0.

Procedure:

1. Transfer 2, 4, 6, 8, 10 ml of standard NaCl solution (which is prepared by weighing

accurately 1.271 g NaCl into a 1 liter standard volumetric flask and dissolving the crystals and

diluting the solution up to the mark with distilled water and mixing. The solution gives 1 ppm

Na/ml) into 50 ml standard volumetric flasks and dilute up to the mark with distilled water.

2. Place the distilled water in the suction capillary of the instrument and set the instrument to

read zero.

3. Place each of the standard solutions in the suction capillary and set the instrument to read

the flame emission intensity 2, 4, 6, 8 and10 respectively (rinse with distilled water between

each reading) using sodium filter (598 nm).

4. Dilute the given test solution up to the mark with distilled water, mix well and place the

solution in the suction capillary and record the reading.

5. Draw a calibration curve by plotting the emission intensity (Y-axis) and volume of NaCl

solution (X-axis).

6. From the calibration curve, find out the volume of the given test solution and from which

calculate the amount of Na in the water sample.

Flame photometer uses/ Applications: 1. For qualitative analysis of samples by comparison of spectral emission wavelengths with that

of standards. 2. For quantitative analysis to determine the concentration of group IA and IIA elements.

For example, a) Concentration of calcium in hard water.

b) Concentration of Sodium, potassium in Urine

c) Concentration of calcium and other elements in bio-glass and ceramic materials.

https://www.studyread.com/calcium-uses-in-everyday-life/


Atomic Absorption Spectroscopy

Atomic absorption spectroscopy (AAS) is a spectroanalytical procedure for the quantitative

determination of chemical elements using the absorption of optical radiation (light) by free atoms

in the gaseous state.

Principle:

• The technique makes use of absorption spectroscopy to assess the concentration of an

analyte in a sample.

• It requires standards with known analyte content to establish the relation between the

measured absorbance and the analyte concentration.

• the electrons of the atoms in the atomizer can be promoted to higher orbitals (excited

state) for a short period of time (nanoseconds) by absorbing a defined quantity of energy

(radiation of a given wavelength).

• The wavelength, is specific to a particular electron transition in a particular element. In

general, each wavelength corresponds to only one element, and the width of an

absorption line is only of the order of a few picometers (pm), which gives the technique

its elemental selectivity.

• The radiation flux without a sample and with a sample in the atomizer is measured using

a detector, and the ratio between the two values (the absorbance) is converted to analyte

concentration or mass using the Beer-Lambert Law.

Instrumentation

The apparatus consist of:

(1) Radiant Source (2) Atomizer (3)light sources (Hollow cathode lamp) (4) Mono chromator

(5) Lenses and Slits and (6) Detectors.

The main components used in the instrument can be described as follows:

(1) Radiant Sources: Generally a hydrogen lamp is used as continuous source of radiation.

(2) Atomizer: Generally burners are used to break the liquid sample into droplets which are then allowed to enter into flame. The droplets are then evaporated and sample element is left in residue. The residue is then decomposed by flame. Thus in this process the sample is reduced to atoms.


(3) Hollow Cathode Lamp: These gases emit sharp line spectra. The hydrogen lamp is a hollow cathode lamp. A hollow cathode lamp emits more than one composite line for each element but the required spectral line can be separated by means of a relatively low dispersion monochromator. Most of lines are non-absorbing lines because they involve transition other than from ground state. (4) Monochromators:

Also it is called wavelengh selector .Generally the mono chromators are gratings and

prisms.

(5) Filters or slits: Filters or slits are used for isolation of required spectral line if element has a simple line spectrum. (6) Detectors: Generally photomultipliers are used as detectors. In some instruments two filters and two detectors are used to compensate the fluctuation in the sources.

Procedure:

• A meter is adjusted to read zero absorbance or 100% transmittance when a blank solution is sprayed into the flame

• light of hollow cathode lamp passes on to photomultiplier tube.

• The solution to be investigated is introduced, a certain part of light is absorbed resulting in decrease of light intensity falling on photomultiplier. This gives a deflection in the meter needle which is noted immediately.

• As this is a comparative method hence standard solutions of elements are used to make a calibration curve from which the concentration of sample elements can be calculated.

APPLICATIONS OF AAS

Water analysis (e.g. Ca, Mg, Fe, Si, Al, Ba content)

Food analysis

Analysis of animal feedstuffs (e.g. Mn, Fe, Cu, Cr, Se,Zn)

Analysis of soils

Clinical analysis (blood samples: whole blood, plasma,serum; Ca, Mg, Li, Na, K, Fe)

Disadvantages of Atomic Absorption Spectroscopy: (1) This technique has not proved very successful for the estimation of elements like V, Si, Mo, Ti and A1 because these elements give oxides in the flame. (2) In aqueous solution, the anion affects the signal to a noticeable degree. (3) A separate lamp is needed for the determination of each element. Attempts are being made to overcome this difficulty by using a continuous source.


NANOTECHNOLOGY

Introduction: Nanotechnology originates from the Greek word meaning “dwarf”. A nanometer

is one billionth (10-9) of a meter, which is tiny, only the length of ten hydrogen atoms, or about

one hundred thousandth of the width of a hair, Although scientists have manipulated matter at

the nanoscale for centuries, calling it physics or chemistry, it was not until a new generation of

microscopes was invented in the nineteen eighties in IBM, Switzerland that the world of atoms

and molecules could be visualized and managed.

Properties of nanomaterials: Physical and chemical properties of nonmaterial’s are

significantly different from those of single atoms/molecules and bulk material of the same

chemical composition.

Difference in properties is related to,

1. The spatial arrangement of molecules/structure,

2. Electronic structure,

3. Energetic,

4. Chemical reactivity

5. Phase change or catalytic activity.

Properties remain same at first (size being reduced from macro to micro), and slowly small

changes begin to take place as the particle size is reduced further from micro to the nanoscale

range (generally observed below, 100 nm).

Size dependent properties

1). Surface area: If a macroscopic object is divided into smaller parts, the ratio of surface atoms

to interior atoms becomes a significant number of total fractions of atoms. The inverse relation

between the particle size and surface area is responsible for the remarkable changes in the

physical properties of nonmaterials.

Properties like catalytic activity, gas adsorption; chemical reaction depends on surface area. Ex:

Gold is catalytically inactive in bulk but nano gold is highly catalytically active.

2). Electrical properties: Electronic bands in bulk material are continuous due to the overlap of

billions of atoms, but in nano-size material very few molecules are present so electrical band

separates. Hence some metals which are good conductors in bulk become semiconductor and

insulator at the nano level.

3). Optical Properties: Nanomaterials exhibit different colors from bulk materials. The discrete

electronic state of nanomaterial allows absorption and emission of light of specified.

4). Thermal properties: The large increase in surface energy and the change in interatomic

spacing as a function of nanoparticle size mentioned above have a marked effect on material

properties. For instance, the melting point of gold particles, which is really a bulk


thermodynamic characteristic, has been observed to decrease rapidly for particle sizes less than

10 nm. Smaller particles have higher melting points.

5). Catalytic properties: Nanomaterial-based catalysts are usually heterogeneous catalysts

broken up into metal nanoparticles in order to speed up the catalytic process. Metal nanoparticles

have a higher surface area so there is increased catalytic activity because more catalytic reactions

can occur at the same time. Nanoparticle catalysts can also be easily separated and recycled with

more retention of catalytic activity than their bulk counterparts.

General methods of Synthesis:

There are two approaches for the synthesis of nanomaterials and the

fabrication of nanostructures. Top down approach refers to slicing or

successive cutting off a bulk material to get nano-sized particle. Bottom-

up approach refers to the build-up of a material from the bottom: atom

by atom, molecule by molecule or cluster by cluster. Both approaches

play very important role in modern industry and most likely in

nanotechnology as well. There are advantages and disadvantages to both

approaches.

Sol-gel process:

The sol-gel method of synthesizing nanomaterial is very popular amongst chemists and is widely

employed to prepare oxide materials.

The sol-gel process can be characterized by a series

of distinct steps.

Step 1: Formation of different stable solutions of

the alkoxide or solvated metal precursor (the sol).

Step 2: Gelation resulting from the formation of an

oxide- or alcohol- bridged network (the gel) by a

polycondensation or polyesterification reaction that

results in a dramatic increase in the viscosity of the

solution.

MOR + H2O → MOH + ROH (hydrolysis)

MOH+ROM→M-O-M+ROH (condn.)

Step 3: Aging of the gel (Syneresis), during which the

polycondensation reactions continue until the gel transforms into a solid mass, accompanied by

contraction of the gel network and expulsion of solvent from gel pores. The aging process of gels can

exceed 7 days and is critical to the prevention of cracks in gels that have been cast.


Step 4: Drying of the gel, when water and other volatile liquids are removed from the gel network. This

process is complicated due to fundamental changes in the structure of the gel. The drying process has

itself been broken into four distinct steps: (i) the constant rate period, (ii) the critical point, (iii) the

falling rate period, (iv) the second falling rate period.

If isolated by thermal evaporation, the resulting monolith is termed a xerogel. If the solvent (such as

water) is extracted under supercritical or near supercritical conditions, the product is an aerogel.

Step 5: Dehydration, during which surface- bound M-OH groups are removed, thereby stabilizing the gel

against rehydration. This is normally achieved by calcining the monolith at temperatures up to 8000C.

Step 6: Densification and decomposition of the gels at high temperatures (T>8000C). The pores of the

gel network are collapsed, and remaining organic species are volatilized. The typical steps that are

involved in sol-gel processing are shown in the schematic diagram below.

Precipitation method

• In this technique, an inorganic metal such as acetate,

chloride, nitrate is dissolved in aqueous medium.

• Metal cations exist in the form of metal hydrate species

such as [Al(H2O)6]3+ and [Fe(H2O)6]

3+.

• When a precipitating agent such as NaOH or NH4OH is

added, these species get hydrolysed with the increase in

pH, condensation of hydrolysed species takes place. These

concentration of the solution is is termed as

supersaturation. At this concentration only, formation of

nucleation initiates. The particles get precipitated into

metal hydroxide.

• The above precipitate is filtered, washed with water and

calcined at higher temperature to remove the counter

anions of the metal salt used such as acetate or nitrate then

finally grinding to get a fine powder.

Chemical Vapour Condensation (CVC) method

• Chemical vapor deposition (CVD) is a chemical process used to produce high quality,

high-performance, solid materials.

• The process is often used in the semiconductor industry to produce thin films. In typical

CVD, the wafer (substrate) is exposed to one or more volatile precursors, which react

and/or decompose on the substrate surface to produce the desired deposit.

• volatile by-products are also produced, which are removed by gas flow through the

reaction chamber.

• Microfabrication processes widely use CVD to deposit materials in various forms,

including: monocrystalline, polycrystalline, amorphous, and epitaxial.

• Deposition can also take place due to a chemical reaction between some reactants on the

substrate.

• In this case reactant gases (precursors) are pumped in to a reaction chamber (reactor).


• Under the right conditions (T, P), they undergo a reaction at the substrate.

• One of the products of the reaction gets deposited on the substrate.

• The by-products are pumped out.

• The key parameters are chemical (reaction rates, gas transport, diffusion).

Nano-scale –materials Nanomaterials have extremely small size which having at least one dimension 100 nm or less. Nanomaterials can be nanoscale in one dimension (eg. surface films), two dimensions (eg. strands or fibres), or three dimensions (eg. particles). They can exist in single, fused, aggregated or agglomerated forms with spherical, tubular, and irregular shapes. Common types of nanomaterials include nanotubes, dendrimers, quantum dots and fullerenes. Nanomaterials have applications in the field of nano technology, and displays different physical chemical characteristics from normal chemicals (i.e., silver nano, carbon nanotube, fullerene, photocatalyst, carbon nano, silica). According to Siegel, Nano structured materials are classified as Zero dimensional, one dimensional, two dimensional, three dimensional nanostructures.

Carbon Nanotubes CNTs are cylinderical tubes with a central hallow core due to rolling up of graphite sheets. CNTs is a one dimensional material like nanowire but with the aspect ratio (length/ width) greater than 1000. Types of CNTs

There are two types of CNTs 1) Single - walled carbon Nano Tubes (SWCNTs) :- They are formed by rolling up of single graphite layer. 2) Multi - walled carbon Nano Tubes (MWCNTs) :- They consist of two or more concentric graphene cylinders with vanderwaals forces between adjacent tubes.


Synthesis of Carbon Nanotubes: - Propylene is fed into the reaction maintained at 800oC using

an anodic aluminum oxide film as template with carrier N2 gas. It undergoes paralytic

decomposition depositing uniform layer of carbon on the inner wall of the template nano

channels. "Catalytic Carbon Vapor Deposition" method for producing Carbon Nanotube Technologies.

This proven industrial process is well known for its reliability and scalability. It involves growing

nanotubes on substrates, thus enabling uniform, large-scale production of the highest-quality carbon

nanotubes worldwide.

1. In 1991, during the optimization of the fullerene-

synthesis by arc discharges, small tubes were found

(by Sumio Iijima, characterized by transmission

electron microscopy TEM).

2. Nanotubes are members of the fullerene structural

family

3. These sheets are rolled at specific and discrete

("chiral") angles.

4. Individual nanotubes naturally align themselves into

"ropes" held together by van der Waals forces.

5. Nanotubes are categorized as single-walled

nanotubes (SWNTs) and multi-walled nanotubes

(MWNTs) and Double-wall Nanotubes (DWNT).

6. The chemical bonding of nanotubes is composed

entirely of sp2 bonds, similar to those of graphite. These bonds, which are stronger than

the sp3 bonds found in alkanes and diamond, provide nanotubes with their unique

strength.

Properties: 1. Carbon nanotubes are the strongest and stiffest materials yet discovered in terms of

tensile strength (~100 GPa) and elastic modulus respectively (due to covalent sp2 bonds).

2. Standard single-walled carbon nanotubes can withstand a pressure up to 25 GPa without

deformation.

3. Maximum electrical conductance of a single-walled carbon nanotube is 2G0,

4. All nanotubes are expected to be very good thermal conductors along the tube, exhibiting

a property known as "ballistic conduction".

Applications: Conductive plastics, Structural composite materials, Flat-panel displays, Gas

storage Antifouling paint, Micro- and nano-electronics, Radar-absorbing coating, Technical

textiles , Ultra-capacitors, Atomic Force Microscope (AFM) tips, Batteries with improved

lifetime, Biosensors for harmful gases, Extra strong fibers.

Fullerenes

Fullerene a new allotrope of carbon, in which the atoms are arranged in closed shells, having the

structure of a truncated icosahedron (a polyhedron).


Synthesis of Fullerenes Graphite is vaporized by setting up an electric arc between two graphite electrodes in

a controlled atmosphere of helium gas. The temperature at the tip of electrode is more than

4000oC and pressure of He gas is 150 - 200 torr. A mixture of

various fullerenes is obtained by condensing the evaporated carbon

and the main product is the fullerene C60. It is extracted and crystallized using benzene as solvent.

1. First time produced isolable quantities of C60 by causing an arc

between two graphite rods to burn in a helium atmosphere.

2. Other carbon clusters such as C70, C76, C78 and C84 are also

studied, with new and unexpected properties.

3. Fullerenes consist of 20 hexagonal and 12 pentagonal rings as the

basis of an icosahedral symmetry closed cage structure, with

each carbon atom is bonded to three others and is sp2 hybridised.

4. C60 molecule has two bond lengths - the 6:6 ring bonds can be

considered "double bonds" and are shorter than the 6:5 bonds.C60 is not "super aromatic" as

it tends to avoid double bonds in the pentagonal rings, resulting in poor electron

delocalisation and hence C60 behaves like an electron deficient alkene, and reacts readily

with electron rich species.

5. The most striking property of the C60 molecule is its high symmetry. There are 120 symmetry

operations (most symmetric molecule), like rotations around an axis or reflections in a plane,

which map the molecule onto itself.

Applications

Fullerenes have been extensively used for several biomedical applications including the design

of high-performance MRI contrast agents, X-ray imaging contrast agents, photodynamic therapy

and drug and gene delivery.

Graphenes

• Graphene is a semi-metal with a small overlap between the valence and the conduction bands. It is an allotrope of carbon consisting of a single layer of carbon atoms arranged in a hexagonal lattice.

• It is pure carbon in the form of a very thin, nearly transparent sheet, one atom thick. carbon atoms are densely packed in a regular sp2-bonded atomic -scale chicken wire (Hexagonal) pattern.

• Graphene can be described as a one-atom thick layer of graphite. It is the basic structural element of many other allotropes of carbon, such as graphite, diamond, charcoal, carbon nanotubes and fullerenes.

• Graphene is a crystalline allotrope of carbon with 2-dimensional properties. Its carbon atoms are densely packed in a regular atomic-scale chicken wire (hexagonal) pattern.


• Each atom has four bonds: one σ bond with each of its three neighbors and one π-bond that is oriented out of plane. The atoms are about 1.42 Å apart.

• Graphene's hexagonal lattice can be regarded as two interleaving triangular lattices. This perspective was successfully used to calculate the band structure for a single graphite layer using a tight-binding approximation.

• Graphene's stability is due to its tightly packed carbon atoms and a sp2 orbital hybridization – a combination of orbitals s, px and py that constitute the σ-bond. The final pz electron makes up the π-bond. The π-bonds hybridize together to form the π-band and π∗-bands. These bands are responsible for most of graphene's notable electronic properties, via the half-filled band that permits free-moving electrons.

Applications

• Graphene is a transparent and flexible conductor that holds promise for various

material/device applications, including solar cells, light-emitting diodes (LED), touch panels

and smart windows or phones.

• Graphene has also been used in other fundamental electronic devices, such as capacitors and

Field Effect Transistors (FETs).

Most probable questions:

1. Discuss the instrumentation and applications of conductometric estimation strong acid vs strong base. (L5)

2. Explain the principle working and applications of potentiometry (L2)

3. Mention the advantages of Conductometric titration(L2)

4. State Beer‘s law and Lambert‘s law. Explain the colorimetric estimation of copper (L2)

5. Discuss the application of Conductometry in the determination of the amount of CH3COOH using

std, NaoH solutions (L5)

6. Discuss the instrumentation and applications of flame photometric estimation Na and K (L5)

7. Discuss the instrumentation and applications of atomic adsorption spectroscopy.(L5)

8. What is a nanomaterial ? How they are different from bulk matrials? (L1)

9. Explain the Sol-gel method for preparation of nanomaterial with an example.(L2) 10. Explain the precipitation method for preparation of nonmaterial with an example.(L2)

11.Explain the CVD method for preparation of nonmaterial with an example.(L2) 12. Give the synthesis, properties and applications of carbon Nano tube.(L2) 13. What are Nano composites? Give the properties and applications?(L1) 14. Give the structural features, properties and applications of Buckminster fullerenes.(L2) 15. What is Dendrimers? Give the properties and applications?(L1)

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