FIRST YEAR DIPLOMAApplied Science (Chemistry)

E & TC ENGINEERING GROUP G SCHEME 17211 Unit 1: Metallurgy (Marks : 14)

Q.1. Define the term i) Metallurgy ii) gangue iii) Flux iv) slag. 4marksAns. i. Metallurgy: The process of extraction of a pure metal from its ore economically and profitably is known as metallurgy. ii. Gangue: Ore is associated with impurities like sand and clay. These unwanted impurities associated with the ores are known

as gangue or matrix.iii. Flux: Unwanted earthy impurities present in the ore are removed by the chemical methods, the substances used to remove

unwanted impurities associated with ore are known as flux.iv. Slag: Slag is easily melting chemical compound formed by the reaction of gangue and flux added. ----------------------------------------------------------------------------------------------------------------------------------------------------------Q.2. Define metallurgy. Name the different ores of copper 3 marksAns. Metallurgy: The process of extraction of a pure metal from its ore economically and profitably is known as metallurgy. Most copper occurs in compound form, mainly as sulphides and oxides. The main ores of copper are:(a) copper pyrites (CuFeS)(b) copper glance (Cu2S)(c) cuprite (Cu20)(d) malachite [CuCO3.Cu(OH)2](e) azurite [2CuCO3.Cu(OH)2]____________________________________________________________________________________________Q.3 What are the steps involved in extraction of copper from its sulphide ore. 2marksCopper is mainly extracted from copper pyrites using the dry process. The main stages involved in the extraction process are:(a) concentration(b) roasting(c) smelting(d) Heating in a convertor (Bessemerization)(e) refining _________________________________________________________________________________________ Q 4 Which physical method is used to concentrate the sulphide ore. Explain it with the help of diagram. 4 marksAns. Fourth floating method is used to concentrate the sulphide ore. Copper pyrite (CuFeS2) are concentrated by this method. Figure:

Froth Floating Process:

Principle: This method is based on the wetting properties of ore and gangue particles with the frothing agent (oil) and water. The sulphide ore is wetted by oil and gangue particles by water.

Process: In this process, powdered sulphide ore is mixed with water and pine oil. The whole mixture is then stirred vigorously by passing compressed air. The oil forms a froth with air bubbles. The sulphide ore particles get attached with the froth and floats on the surface, while the gangue or earthy impurities are wetted by water and sink to the bottom of the tank. The floating froth is then skimmed off into settling basin from

where by filter press a concentrated ore is recovered. --------------------------------------------------------------------------------------------------------------------------------------------------------Q.6 Describe the process of roasting of copper ore giving chemical reactions. 4marksRoasting: It is the process in which concentrated ore is heated strongly in a current of air in the hearth of the reverberatory furnace. During roasting the following changes take place.

a) The sulphides of copper and iron are partially oxidized. 2Cu2S + 3O2 2Cu2O + 2SO2

2FeS + 3O2 2FeO + 2SO2

b) The pyrite is converted into cuprous sulphide and ferrous sulphide with evolution of sulphur dioxide. 2CuFeS2 + O2 Cu2S + 2FeS + SO2

c) Free sulphur is oxidized and removed as sulphur dioxide. S + O2 SO2

d) The arsenic and antimony present in the ore are removed as volatile oxides.

4As + 3O2 2As2O3

4Sb + 3O2 2 Sb2O3

------------------------------------------------------------------------------------------------------------------------------------Q.7 Describe the smelting process of copper ore with neat and labeled diagram. 4marksSmelting: It is the process in which roasted ore is mixed with coke and silica and heated srongly at 1350 o in the water jacketed blast furnace in presence of excess air. Construction of blast furnace:The blast furnace is made up of steel lined inside with refractory bricks. It is about 15 to 20 feet in height and it is water jacketed throughout. Outlet is provided near the top for removal of waste gases. The mixture is heated strongly in the presence of air. The air blast enter the furnace through the tuyeres.

The following changes occure in the blast furnace. In the blast furnace, the oxidation of ferrous sulphide which started during the roasting process continues:

2FeS + 3O2 2FeO + 2SO2

The iron (II) oxide formed combines with sand to form a fusible slag. This is removed as slagFeO(s) + SiO2(s) FeSiO3 (slag)

Cuorous oxide reacts with ferrous sulphide and forms cuprous sulphide and ferrous oxide because iron has high affinity for oxygen than copper. Cu2O + FeS Cu2S + FeO The molten mass containing mainly copper sulphide with a little amount of iron sulphide(Cu2S + FeO) is known as matte. It is taken out through the lower tap hole.

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Q.8 Describe process of Bessemerisation of copper ore with neat and labeled diagram. 4marksBessemerization: The molten matte is transfered to a Bessemer converter a pear shaped furnace made up of steel plate and provided with a basic lining of lime. It is fitted with pivots/trunium and can be mounted in any direction. In the convertor, air is mixed with sand and blown through hot molten matte (Cu2S + FeO). The purpose of Bessemer convertor is to convert matte (Cu2S + FeO) into blister copper containing about 96-98% copper.

The following reactions occur in the Bessemer converter. 1. Remaining ferrous sulphide gets oxidized to ferrous oxide.

2FeS + 3O2 2 FeO + 2SO2

Ferrous oxide combines with silica and forms ferrous silicate as slag. This slag is drained out at intervels by tilting the vessel. FeO +SiO2 FeSiO3

3. Cuprous sulphide is oxidized partially to Cu2O. 2Cu2S + 3O2 2Cu2O + 2SO2

This cuprous oxide combines with remaining cuprous sulphide to form free copper metal. This presents an example of auto reduction.

Cu2S + 2Cu2O 6Cu + SO2

The molten copper is poured off and allowed to cool. During cooling the dissolved sulphur dioxide comes out and large blisters are formed on the surface. Hence, the metal formed is given the name blister copper. Blister coller consist of 98% copper and 2% impurities._________________________________________________________________________________________Q. 9 Why blister copper is electro refined? 2Blister copper consists of 3 to 5% impurities of sulphur, arsenic, zinc, iron, nickel, silver platinum gold etc. Due to these impurities, the impure copper is not used for electrical conductivity, because the conductivity is lowered by the traces of impurities present in it. Copper having 100% purity is required for electrical conductivity. So the impure (or crude) copper is refined.Q. 10 Describe with figure electrolytic refining of copper. 4Electrolytic refining: The crude copper obtained contains 98 % copper and remaining impurities. It is further refined to contain 99.98 % copper by electrolytic refining.Figure:

Process: The refining tank is a wooden vat lined with lead sheets. An aqueous solution of 15 % copper sulphate, acidified with 5 to 10 % H2SO4 is used as electrolyte. Impure blister copper plates are made anode and thin plates of pure copper are made cathode. When current of electricity is passed, anode starts dissolving due to oxidation whereas copper cathode becomes thicker due to decomposition of copper.

Chemical reactions: At cathode: Cu2+ +2e- Cu At anode: Cu Cu2+ + 2e-

Thus pure copper is transferred from anode to cathode. Impurities such as Zn, Fe, Ni etc pass into solution as ions. Impurities such as gold, silver and platinum fall under anode as anode mud.

Q.11 Write the physical properties of copper. 2 marksPhysical Properties1. Copper has a characteristic reddish brown colour.2. Its density is 8.93 g cm-3.3. Its melting point is 10830C.4. It is highly malleable and ductile at ordinary temperature. It becomes brittle near melting point.5. It is a very good conductor of heat and electricity.6. Its conductivity is almost as much as that of silver, the best conductor among all the metals.___________________________________________________________________________________________Q.12 Explain the following chemical properties of copper with chemical equations-

a) Action of air b) Action of water c) Action of acid d) Action of alkali 3marksAns: a) Action of air: Copper is not attacked by dry air at ordinary temperature. When it is heated to red hot in presence of air/oxygen, first forms cuprous oxide (Cu2O) and finally cupric oxide (CuO). Cu + 3O2 2Cu2O3 2Cu + 2O2 2CuO

b) Action of water: Copper does not decompose water at ordinary temperature. But in white heat, steam acts upon it to form oxide. Cu + H2O CuO + H2

c) Action of acid: Non oxidising acids like HCI, dilute H2S04 does not copper in the absence of air or oxygen. In presence of air, such acids dissolve the metal forming corresponding salt and water. Cu + HCl + ½ O2 CuCl2 + H2O Cu + H2SO4 + ½ O2 CuSO4 + H2O_________________________________________________________________________________Q.13 Write uses of copper. 4Ans: Uses of copper:1. Due its high electrical conductivity, it is used in making wires and cables.2. It is resistant to corrosion by air and water, hence it is used in making utensils, containers, kettles, coins, ornaments etc.3. It is used in electroplating and electrotyping.

4. The salts of copper have a variety of uses such as disinfectant, fungicide and for coloring glass. 5. Copper forms number of useful alloys.

Eg. With Zn it forms brass(Cu-Zn), with tin bronze (Cu-Sn), with Ni monel metal etc. 6. Copper combines with aluminium to form duralumin which is widely used in constuction of aeroplanes. _____________________________________________________________________________________ Q. 14 What is metallurgy? Give three names of important ores of Aluminium. 3marksMetallurgy: The process of extraction of a pure metal from its ore economically and profitably is known as metallurgy. Names of important ores of Aluminium:

Sr. No. Type Ore Composition

1 Oxides: Bauxite Al2O3 . 2H2O2 Fluoride Cryolite Na3AlF6

3 Silicates Felspar KAlSi3O6

4 Sulphates Alunite K2SO4, Al2 (SO4)3 . 4Al(OH)3

Q. 15 What are the steps in extraction of Al from its ore.Ans: 1. Purification of bauxite by Baeyer's process 2. Electrolytic reduction of pure alumina in a bath of fused cryolite (Na3AlF6) which acts as a flux. 3. Electrolytic refining of aluminium by Hoope’s process.

Q. 16 Describe Bayer’s process for concentration of alumina. 4marksAns: Purification of bauxite by Baeyer's process: Bauxite is always associated with Fe2O3, SiO2 and TiO2 impurities. Bauxite with high percentage of Fe2O3 is called as red

bauxite. It is purified by Baeyer's process. In the Baeyer's process, the bauxite ore is heated with concentrated NaOH solution under pressure (Aluminum is purified by

leaching method). The alumina dissolves as sodium meta aluminate. Al2O3 + 2NaOH 2NaAlO2 + H2O

The other material present in the ore like Fe2O3, TiO2 impurities are left as insoluble part. Greater part of silica also remains unaffected.This solution is filtered to remove impurities.

The filtrate containing sodium meta aluminate is hydrolysed to precipitate Al(OH)3. NaAlO2 + 2H2O NaOH + Al(OH)3

The precipitated Al(OH)3 is dried and ignited at 1200 to1300oC to get pure alumina (99.5 % Al2O3) . 2Al(OH)3 Al2O3 + 3H2O

Q. 17 Why is it essential to purify Bauxite before electrolysis? 2marksAns: Bauxite is always associated with Fe2O3, SiO2 and TiO2 impurities. It contains about 50-60 % alumina. Hence bauxite is purified by Baeyer's process to remove impurities and increase percentage of alumina upto 99.5 %..

Q. 18 Why bauxite cannot be reduced with carbon like iron? 2Ans: Aluminium is more reactive than carbon and so cannot easily be displaced. Therefore it is extracted using electrolysis.But aluminium oxide has such a high melting point that is isn’t practical to electroylse molten aluminium oxide. Instead it is dissolved in molten cryolite and then electrolysed.Q. 19 Describe the process of electrolytic reduction of alumina with figure. 4Ans: Electrolytic reduction of alumina: The alumina is dissolved in a mixture of molten cryolite (Na3AlF6) and CaF2 which lowers the melting point of alumina. It is then electrolysed in a rectangular steel tank with carbon lining, which serves as cathode. Anode is set of thick carbon rods suspended from the top into the fused Al2O3. The temperature is maintained between 900 and 950 oC. Oxygen is evolved at the anode. Al2O3 2Al3+ + 3O2-

At cathode: 2Al3+ + 6 e_ 2AlAt anode: 3O2- 1½ O2 + 6 e- Aluminium formed at the cathode gets collected at the bottom of the electrolytic cell from where it is removed periodically. The

metal obtained by this method is about 99% pure.

Q. 20 Describe electrorefining of aluminium by Hoope’s process. 4marks Ans: Further purification of aluminium obtained by electrolytic reduction process is carried out by lectrolytic refining method. The electrolytic refining of aluminum is carried out in Hoope's cell.

The cell consist of iron tank having a lining of carbon. It has three layers of molten liquids with different densities.

1. The bottom layer is of molten impure aluminum, copper and silicon which acts as anode. 2. The middle layer is a mixture of molten cryolite(Na3AlF6) and BaF2. This mixture acts as the electrolyte.3. Top layer consists of molten pure aluminum in which a number of carbon electrodes are suspended. These carbon electrodes

act as the cathode. When electric current is passed, the aluminium ions from the middle layer move to the top layer and are discharged at the cathode

as pure aluminium. At the same time, an equivalent amount of aluminum from the bottom layer migrates to the middle layer leaving behind the impurities. The pure aluminum is removed from the tapping hole from time to time.

Q. 21 Write the physical properties of aluminium. 2Ans: Physical properties of aluminium:

1. It is a bluish white metal.2. It is very good conductor of heat and electricity.3. It is very light metal (specific gravity 2.7).4. It is malleable and ductile.5. It melts at 658 oC and boils at 1800 oC.6. It reflects light nicely.7. It is a highly corrosion resistant metal.

___________________________________________________________________________________________Q. 22 Explain the following chemical properties of aluminium with chemical equations-

a) Action of air b) Action of water c) Action of acids d) Action of alkali. 4marks

Ans: Chemical Properties of aluminium:

a) Action of air:Dry air has no action on the metal but in moist air it forms a thin film of oxide on its surface. On heating strongly in the presence of air it burns with a brilliant white light 4Al + 3O2 2Al2O3

b) Action of Water:Pure cold water has no effect on the metal but boiling water is decomposed by the metal to form hydrogen.2Al + 6H2O 2Al(OH)3 + 3H2

c) Action of acids: Aluminum sloly reacts with dil H2SO4 which evolves H2 gas. 2Al + 3 H2SO4 2Al2(SO4)3 + 3H2

Aluminium dissolves in hot and conc. H2SO4 with liberation of SO2 gas. 2Al + 6H2SO4 2Al2(SO4)3 + 6H2O + SO4

Aluminum reacts with HCl to form AlCl3. 2Al + 6HCl 2AlCl3 + 3H2

d) Action of alkali: Aluminum reacts with strong alkali like NaOH to form sodium aluminate and H2 gas. 2Al + 2NaOH + 2H2O 2NaAlO2 + 3H2

____________________________________________________________________________________________Q. 23 Write uses of Aluminum. 4marksAns. 1. Aluminum, being very light metal, is used for aeroplane parts, trucks, automobiles, surgical insuments. 2. It is good conductor of electricity, hence used for conducting wires and cables. 3. For making mirrors of telescope and optical instruments. 4. It forms an extremely thin foil, which are used as wrappers for food stuffs. 5. It is used in thermite mixture for reduction of Fe, Cr and Mn. 6. It is good conductor of heat and corrosion resistant, hence used for making utensils, containers for dairy._____________________________________________________________________________________________Q. 24. Describe the process of anodizing of aluminium. 4marks

___________________________________________________________________________________________Q.25 Write composition, properties and applications of the following alloys :(i) Woods metal. ( ii ) Rose metal.Ans: Sr. No.

Name of Solders

Composition Properties Applications

1 Soft Solders Pb = 37-67 %Sn = 60 -31 %Sb = 2-3 %

It melts at low temperature. 1) It is used for soldering electrical connections.

2)Sealing for tin cans. 3)Joining lead pipes.

2 Tinmann’s Solders

Sn = 66 %Pb = 34 %

It melts at 180oC 1)It is used for joining articles of tin.

3 Brazing Solders

Sn = 92 %Sb = 5.5 %Cu = 2.5 %

It melts at low temperature. 1) It is used for soldering steel joints by the process of fusion

4 Rose metal Bi = 50 %Pb = 28 %Sn = 22 %

It is readily fusible at 88oC. 1) It is used in making fire alarm.2) Casting for dental work.3) Fuse wires. 4) In automatic water sprinklers.

5 Plumber’s Solders

Sn = 2 partsPb = 1 parts

It begins to solidify at 240oC and passing through a pasty stage solidifies at 180oC

It is used in potable water piping.

Unit 2: Corrosion Marks : 14

Q. 1 Define corrosion. Mention types of corrosion. 2Ans. Corrosion: Any process of chemical and electrochemical decay or destruction of metal due to the action of surrounding medium is called corrosion. Types of corrosion:

1) Atmospheric corrosion (direct chemical corrosion) 2) Immersed corrosion (electrochemical corrosion)

_______________________________________________________________________________________________ Q.2. What is meant by rusting.Ans: The atmospheric corrosion of iron and steel, leading to the formation of a layer of reddish scale and powder of oxide of Fe 3O4 on the surface._______________________________________________________________________________________________Q. 3 Define atmospheric corrosion. Explain its principle with one example. 4Ans. Corrosion caused by direct chemical action of atmospheric gases such as oxygen, halogens, CO2, SO2, H2S etc. with metal surface is called as atmospheric corrosion. Corrosion brought about by atmospheric conditions is called atmospheric corrosion.Principle:When the metal surface is exposed to air, it is attacked by gases present in the surrounding medium and gets coated with corresponding compounds like oxides, sulphides, basic carbonates etc. Examples: 1) Rusting of iron due to forming reddish scale of Fe2O3 on surface.

2) Formation of green film of basic carbonate on surface of copper when exposed to moist air containing CO2.

________________________________________________________________________________________________Q. 4 Write mechanism of corrosion of a metal due to action of oxygen (due to oxidation). 2Ans. The metal surface when exposed to air undergo oxidation. A thin layer of metal oxide forms on the metal surface. 2M + O2 2MO (M- metal, MO- metal oxide)Mechanism of oxide film formation is represented by following equation. M M2+ + 2e- (oxidation: loss of electrons) O + 2e- O2- (reduction: gain of electrons) _____________________________________ Net reaction: M + O M2+ + O2 - MOIn above reaction, the metal is oxidized to form M2+ ion and oxygen is oxidized to form O2 – ion. These ions combine to form metal oxide (MO). The electrons are transferred from metal atom to oxygen.Q. 5 Give the types of oxide films formed on metal surface due to action of oxygen and their significance. 4Ans: The metal surface when exposed to air undergo oxidation. A thin layer of metal oxide forms on the metal surface. Types of oxide films: a) Stable oxide film – i) Porous film (Non-protective film) ii) Non-porous film (Protective film) b) Unstable oxide film c) Volatile oxide filma) Stable oxide film: The stable oxide film has fine grain structure and it sticks the metal surface tightly. Depending upon the nature of film, futher corrosion of metal may stop or continue. The stable metal oxide film is of two types as given below. i) Non-protective film (Porous film (Non-protective film): The oxide films of alkali metals (like Li, K, Na) and alkaline earth metals (like Ca, Sr, Mg) have volume less than the volume of metal. Such a film is insufficient to cover surface area of the metal completely. Consequently. the oxide layer faces stresses and strains and develop cracks and pores in its structure. Oxygen attacks the metal through cracks and pores and thus corrosion continues. ii) Non-porous film (Protective film): The metals like aluminium, tin, copper, lead form oxide film on the surface which has volume is greater than the volume of metal. It does not contain pores or cracks. Such a film is sufficient to cover surface area of the metal. It protects the metal from futher attack of oxygen and corrosion stops.

b) Unstable oxide film: When the oxide film is unstable, it decomposes back into the metal and oxygen, as soon as it is formed. 2M + O2 2MO Therefore, corrosion is not possible in case of noble metals such as silver, gold, platinum etc. c) Volatile oxide film: When the oxide film is volatile, it vaporizes as soon as it is formed. Hence, continuously the fresh metal surface is exposed to atmosphere and corrosion continues e.g. molybdenum oxide (MoO3) and stannic chloride (SnCl4) are volatile films.Q. 6 Distinguish between corrosion of magnesium and aluminium due to action of oxygen. 2Ans: Magnesium forms MgO film on its surface whose volume is less than the volume of magnesium. It is insufficient to cover the surface completely as it is porous. Hence corrosion continues through cracks and pores.

The tendency of aluminium to oxidation, is much greater than iron but the film of aluminium oxide (Al2O3) formed on the surface of aluminium is extremely adherent, non-porous (protective). Due to the absence of any pores or cracks in the oxide film, it forms a barrier for further action and therefore, the rate of oxidation of aluminium rapidly decreases.______________________________________________________________________________________Q. 7 State the factors affecting the rate of atmospheric corrosion. 2Ans: Factors affecting atmospheric corrosion:(1) Impurities in the atmosphere. (2) Moisture in the atmosphere. (1) Impurities in the atmosphere : Air in the industrial towns contain traces of carbon dioxide, hydrogen sulphide, sulphur dioxide gases, fumes of acids etc. In the presence of such impurities corrosion becomes faster. (2) Moisture: The rate of corrosion increases in presence humidity (moisture). Moisture dissolves the atmospheric gases or chemical vapors and the reaction between such dissolved gases with metallic surface becomes faster. Hence, water can act as a conducting medium and promotes corrosion. For example, rusting of iron is promoted in humid atmosphere. Q. 8 Define electrochemical/immersed corrosion. Explain its principle. Write examples. 4Ans: Electro-chemical corrosion( Immersed corrosion): The corrosion which takes place due to action of moisture, water or solutions when two dissimilar metals are in contact with each other. It is a common type of corrosion of metal in aqueous corrosive environment. This type of corrosion occurs when the metal comes in contact with a conducting liquid or when two dissimilar

metals are immersed or dipped partly in a solution. This type of corrosion occurs at a solid-liquid interface. The electro-chemical corrosion takes place by the formation of two types of electrolytic cells:a) Galvanic cells are set up when two dissimilar metals come in contact with each other and are surrounded by

moist air or liquid medium.b) Concentration cells are set up when a single metal is surrounded by moist air with difference in concentration of

ions in solution or oxygen. _____________________________________________________________________________________________Q. 9 Write examples of electrochemical corrosion. 2marksAns: 1) Rusting of fencing Wire under joints.

2) Corrosion at riveted joints. 3) Steel pipe connected to copper plumbing. 4) Lead-antimony Solder around copper wire 5) Steel screws in marine brass-hardware 6) Copper sheets joined by iron nails.

Q. 10 Describe the mechanism of corrosion by formation of a Galvanic cell. 4 marks

Ans: Electrochemical corrosion takes place by forming Galvanic cell when two dissimilar metals come in contact with each other and are surrounded by moist air or liquid medium.

Working of galvanic cell can be explained by considering a Daniel cell.It consists of copper and zinc plates dipped in CuSO4 and ZnSO4 solutions respectively. The solutions are separated by a porous partition The plates are connected by metallic conducting wires. The emf developed is due to the two separate reactions taking place at the electrodes. Zinc metal which is higher in electrochemical series acts as anode and goes into the solution as Zn++ ions. The electrons flow from Zn to Cu. Zn Zn++ + 2e- ( Oxidation)Copper being lower in electrochemical series acts as cathode. Cu++ ions receive

electrons from cathode to get discharged as copper metal. Cu++ + 2e- Cu ( Reduction)As a net result, Zn anode corrodes and Cu cathode is protected from corrosion.

Q. 11 Explain the mechanism of electrochemical/immersed corrosion by evolution of hydrogen gas. 4Ans: Electrochemical corrosion takes place by forming Galvanic cell when two dissimilar metals come in contact with each other and are surrounded by moist air or liquid medium. If the surrounding medium is acidicsolution, then anodic area corrodes while H2 gas evolves at the cathode.

1) It occurs usually in acidic environments like industrial waste, solutions of non oxidizing acids like HCl. 2) For example, consider a steel tank containing acidic industrial waste and small piece of copper scrap in contact with the steel. 3) The steel tank acts as anode and small piece of copper scrap as cathode.4) The portion of the steel tank in contact with copper is corroded most with loss of two electrons.

Fe Fe++ + 2e- 5) The electrons flow through the metal from anode to cathode. At cathode, H + ions of acidic solution are eliminated as hydrogen gas. 2 H + + 2e- H2 (gas)

In such cases cathodic area is much larger than the anodic area.__________________________________________________________________________________________________________________________________________________

Q. 12 Explain the mechanism of electrochemical/immersed corrosion by absorption of oxygen gas. 4Ans: Electrochemical corrosion takes place by forming Galvanic cell when two dissimilar metals come in contact with each other and are surrounded by moist air or liquid medium. If the surrounding medium is neutral or slightly alkaline, then anodic area corrodes while O2 gas is absorbed at the cathode.Rusting of iron under water drop or neutral NaCI solution.

For example, consider iron sheet whose surface is coated with a thin film of iron oxide. If this iron oxide film has some cracks, then in prence of water drop electrochemical corrosion occurs. The cracked part

acts as anode while the remaining sheet acts as cathode. At the anodic areas iron dissolves as Fe++ ions in water drop.

The liberated electrons flow from anodic to cathodic areas, through iron metal.Anode reaction: Fe Fe++ + 2e- Cathode reactions: Atmospheric oxygen is absorbed in water drop. H2O, oxygen and 2e- form OH- ions. They react with Fe++ to form Fe(OH-)2 which further oxidizes to yellow rust. 2H2O + O2 + 2e- 4(OH- ) Fe++ + 2OH- Fe(OH-)2 Fe2O3.H2O( Rust)In such cases anodic area is much larger than the cathodic area.Q. 12 Name the factors affecting electrochemical/immersed corrosion. 2marksAns: 1. Position of metal in electrochemical series. 2. pH value. 3. Solubility of corrosion products.

4. Hydrogen overvoltage. 5. Physical difference of the metallic surface.6. Differential aeration.

______________________________________________________________________________________Q. 13 Describe the factors affecting electrochemical/immersed corrosion. 4marksAns: 1. Position of metal in the electrochemical series : In the electrochemical series, more electropositive metals occupy upper position. These metals have great

Steel tank(anode)

Acidic waste solution

tendency to go in solution as positive metallic ions and hence they get corroded. The metals occupying lower position have less tendency to get corroded.2. pH-value: pH value of the solution indicates acidic, neutral or basic nature. As a rule, acids are more corrosive to metals than neutral or basic solutions.3. Solubility of the corrosion products : Due to corrosion,a thin film of corrosion product forms on the metal surface. The corrosion film may be soluble or insoluble. If it is soluble, it gets easily removed exposing surface of metal for further corrosion. If the film formed is insoluble or slightly soluble, it sticks to the metal surface and so resists further corrosion to some extent. 4. Hydrogen over-voltage : The presence of impurities with low hydrogen over-voltage increase the rate of corrosion, while the presence of impurities with high over-voltage decreases the rate of corrosion of the metal.5. Physical difference of the metallic surface : It has been observed that the uneven surface of metal corrodes at a faster rate than even surface. In such cases, the troughs are less oxygenated and become anodes. The crests are more oxygenated, become cathodes. Corrosion occurs at troughs. Differential aeration : This occurs when one part of the metal is exposed to a different air concentration than the other. It has been found that, poor or least-oxygenated part is anodic to the remaining part of metal and it is corroded.-------------------------------------------------------------------------------------------------------------------------------------------

Q. 14 What are the general methods used for protecting metals from corrosion. 4Ans: The different methods used for the prevention of corrosion are discussed below : 1. Purification of metal (modification of properties of metal): Metal should not contain impurities which are less ac-

tive than metal itself. The impurities which are less active than metal become cathodic and metal anodic. Therefore, metal corrodes faster. Pure metal offers maximum resistance to corrosion.

2. Alloy formation: Metal should be alloyed with other metals to stop corrosion. Alloys of iron containing silicon, nickel, chromium etc. offer very good resistance to corrosion.

3. Cathode protection (making the metal cathodic): Metal can be protected by making it cathode i.e. it is more ac-tive impurity. The impurity acts as anode and corrodes protecting the metal.

Underground pipe lines can be protected from corrosion by connecting them to magnesium bars placed in the earth. Magnesium acts as anode and suffers rusting and thus protects pipe lines.

4. Controlling the extemal conditions(modification of environment): Metals should not be brought in contact acids, solids stray current of electricity, circulating water containg dissolved oxygen. It should also be prevented from alter-nate wetting and drying.

5. Applications of protective coatings(use of protective coatings): Metal can be protected from corrosion by apply-ing organic or inorganic protective coating on its surface.Organic coating: eg. Paint coating Inorganic coating: eg. Metal coating.

Q. 15 What is sacrificial anodic protection? 3 Ans: Sacrificial anodic protection is a type of cathodic protection. In

this type of protection, anode produces a current that will move from the anode to the cathode (structure) within the electrolyte. The metals used should

be more electronegative than steel such as magnesium and Zinc.The applications of cathodic protection: pipelines, ships, marine structures, steel in concrete, internal surfaces of tanks, etc.

_____________________________________________________________________________________.Q. 16 Describe impressed current cathodic protection. 3

Any metallic structure buried or immersed in water or solution can be protected by this method. The current is supplied by a DC generator

such as a transformer-rectifier. The negative pole is electrically connected to the structure to be protected and the positive pole to the anodes such as graphite.

The impressed current is applid in opposite direction to nullify the corrosion current. The metal is converted from anode to cathode and gets protected.______________________________________________________________________________________

Q. 17 Name the methods used for applying protective metallic coatings. 21.Hot dipping: a) Galvanizing b) Tinning2. Metal spraying3. Cementation- a) Sherardizing b) Colorizing c) Chromizing4. Electroplating

5. Metal caddingQ. 18 State the properties of zinc which make it suitable for galvanizing. 2Ans: 1. Zinc has low melting point (419oC) 2. Zinc continues to protect iron even though the coating is broken because it is more electropositive than iron. ___________________________________________________________________________________Q.19. Define galvanizing. Describe the process with the help of diagram. 4Ans. Galvanizing: It is the process of covering iron or steel sheet with a thin coat of zinc to protect it from rusting. Process: 1)The iron article to be galvanized is first cleaned with dilute sulphuric acid to remove any superficial oxide layer and impurities.2) It is then dipped in a bath of zinc ammonium chloride solution and then allowed to dry. 3) The sheet is then dipped in another bath containing molten zinc at temperature 425oC to 460oC. 4)The surface of the bath is kept covered with ammonium chloride to prevent air oxidation. 5)When the sheet is taken out, it is found to have been coated with zinc. 6)Then it is passed through a pair of hot roller to make the coating uniform.

Q. 20 Write the applications and disadvantages of Galvanizing. 4

Ans. Applications of galvanizing: It is widely used for protecting iron exposed to atmosphere as in case of roofing sheets, fencing wires, pipes, bolts, screws, nails, buckets, tubs etc.(Zinc coated steel is not useful but tin coated steel is useful for storing food stuff. 2)Disadvantages of galvanizing: Galvanized ware (zinc coated utensils) cannot be used for preparing and storing food stuffs, especially

which are acidic in nature because zinc gets dissolved in dilute acids forming poisonous zinc compounds which will poison the contents.Q. 21 Why tin is extensively used for coating over mild steel required for food-stuff industry? 2 marks.Ans: Tin is extensively used for coating over mild steel required for food-stuff industry because-

1. It is resistant to action of organic acids and water.

2. Tin is less electropositive metal (nobler) than iron and therefore it is more resistasnt to

chemical attack.3. It has low melting point and hence it can coated by hot dipping process.

Iron or steel sheet

Q. 22 Define tinning. Explain the process of tinning with the help of labeled diagram. 4Ans. Tinning Process: It is defined as the process of covering iron or steel sheets with a thin coat of tin to preotect it from corrosion.1) The sheet of steel to be tinned is first cleaned by dilute sulphuric acid to remove the oxide film and impurities if any. 2) Then it is dipped in a bath containing molten flux of zinc chloride, which helps the molten metal to get adhere to the metal

sheet. 3) Then it is dipped in another bath containing molten tin. 4) Finally it is dipped in a suitable vegetable oil, to protect the hot tin coated surface against oxidation. It is then passed through a series of hot rollers.

5) The rollers remove the superfluous metal and make the coating uniform all over the surface of the metal sheet.

----------------------------------------------------------------------------------------------------------------------------------------------------------------Q. 23 Write applications and advantages of tinning. 4marks

Ans: Applications of tinning: 1. For manufacturing various types of cans for storing food stuffs, biscuit tins, kitchen utensils, oil, ghee, pickle, medicines,

kerosene etc.2. Copper wire to be insulated with rubber is first tinned to prevent attack of sulphur.3. Copper wire is tinned to facilitate soldering.4. Tinned copper sheets are used for soldering.

-------------------------------------------------------------------------------------------------------------------------------------------------------------Q.24. Write the difference between galvanizing and tinning 4matksAns.

----------------------------------------------------------------------------------------------------------------------------------------------------------------Q. 25 Describe the process of metal spraying. Write its advantage and disadvantage. 4marksAns: Metal spraying process: It is defined as the process of developing a protective coating by spraying molten metal on the surface of base metal using spraying gun.

1. The spraying gun consists of a duct for compressed air and fitted with oxy-hydrogen flame. 2. The metal wire is fed into the gun. 3. The metal wire gets melted by oxy-hydrogen flame.4. Molten mass is sprayed on surface of base metal with the help of compressed air.5. The spray can be directed towards the surface to be coated. The sprayed metal adheres to the surface well and protects it from corrosion.

Advantages: 1.It is a handy process. 2.Much labour is not required. 3. Irregular surfaces can be coated efficiently.

Disadvantages: This process is not so much effective as the coating may be porous and less adherent. ---------------------------------------------------------------------------------------------------------------------------------------------------------------Q. 26 Write its applications of metal spraying process. 4marksAns: Applications (advantages) of metal spraying and disadvantages process:

1. Meatallic coating can applied on wood, plastic, glass, ceramic etc. surfaces.2. Metallic coating can be applied to fabricated structures.3. Damaged, cracked and worn out machine parts can be repaired by metal spraying.4. The coatings of metals like Al, Ni, Zn, Sn, Pb etc. can be applied spraying method.

Sr. Galvanizing Tinning

1 It is the process of coating iron sheet with Zinc to prevent it from rusting.

It is the process of coating iron sheet with tin to prevent it from rusting.

2 Zinc is more electropositive than iron. Tin is less electropositive than iron3 In galvanizing, zinc continues to protect the metal if

the coating is broken.In tinning, tin protects the metal till the coating is perfect; a break in coating causes rapid corrosion.

4 Galvanized ware cannot be used for storage of food stuffs which is acidic in nature, as zinc reacts with acids forming zinc compounds which are poisonous.

Tin coating utensils can be used for storage of food stuffs as tin protects the metal from corrosion and avoids poisoning.

-----------------------------------------------------------------------------------------------------------------------------------------------------------------Q. 27 How metal coating can be applied by electroplating? 4

Ans. The process of forming metallic coating of a superior metal (like silver, gold, nickel, chromium) on inferior base metal with the help of electric current is known as electroplating. Let us consider electroplating of silver on iron spoon :

1.A plating of silver on iron spoon is done in a rectangular tank made up of steel.2.Iron spoon is first thoroughly cleaned by boiling with caustic soda to remove grease and dirt if any.3.Then it is washed with water until free from caustic soda. 4.Then it is treated with dilute H2SO4 acid to remove any oxide layer. It is called as prickling. 5.Again it is washed with water, dried and polished carefully.

6.The iron spoon is then made as cathode. The plate of pure silver metal whose coating is desired is made as anode. The cathode and anode both are immersed in cell of potassium argento cyanide, K[Ag (CN)2] or AgNO3.7. When current is passed, the silver anode gets slowly dissolved in solution by giving out Ag+ ions. These Ag+ ions move towards cathode and get deposited. Thus the iron spoon gets plated with smooth and bright deposit of silver. -----------------------------------------------------------------------------------------------------------------------------------------------------------

Q.28 Describe the process of metal cladding. Write the applications of metal cladding. 4Ans. Metal cladding involves bonding firmly and permanently a dense, homogenous layer of coating metal to the base metal on one or both sides.Process:

1) In this method, the base metal to be protected against corrosion is sandwitched or cladded between the two sheets of coating metal.

2) This sandwitch is then passed through two heavy rollers maintained at high temperature.

3) The cladded metal is cathodic with respect to base metal so that the electrolytic protection is provided. Applications of metal cladding:

1) This method is widely used in aircraft industry where alclad sheets are required. 2) Copper claded steel wire widely used for electrical conductors.

Q.29. What is meant by cementation? Name its various types. 4marksAns. 1. Cementation is the process in which base metal is heated with a powder of coating metal.2. In this process an inert or reducing atmosphere is maintained. 3. An alloy of the two metals is formed by diffusion of coating metal into the base metal.4. This method is for producing alloy layer on iron or steel surface with Zn (Sheradizing), Al (calorizing), Cr (Chromizing) etc.

Q. 30 Define and explain Sherardizing process. Write its applications. 4Ans. Sherardizing is a process of coating odd shaped small iron or steel articles with a thin layer of zinc so as to protect them from corrosion.

Procedure: 1) In this process iron article such as nails, bolts, nuts, screw, rivets etc.2) These screw and bolts are taken packed with zinc dust and zinc oxide powder in steel drum. 3) It is provided with electrical heating arrangement to rise the temperature to around 400oC4) It is rotated with the help of motor. 5) Because of rotation, the zinc layer if formed over the articles due to

diffusion and Zn- Fe alloy is formed which protects the iron surface prom corrosion. Advantages. It is used to protect small steel parts against atmospheric corrosion. There is very little change in dimensions of small articles due to formation of very thin layer on iron surface. ---------------------------------------------------------------------------------------------------------------------------------Q. 31 Write the difference between galvanizing and Sherardizing Sr.No Galvanizing Sherardizing

1 It is the process of coating iron sheet with thin coat of Zinc by hot dipping.

It is the process of covering small iron articles by alloying at the surface of base metal.

2 This process is carried out in a large tank by dipping iron sheet in a bath of molten zinc by covering a bath of with ammonium chloride flux.

The process is carried out in rotating closed drum like furnace by packing the small iron articles with zinc powder.

----------------------------------------------------------------------------------------------------------------------------- ---------------------------- Paint

Q. 32 Define paint. Write the characteristics of paint. 4

Q.33 What are the purposes of applying paint.2

Q.34 Name the constituents of paint and write their functions. 4

Q.35. Formation of which type of metal oxide cause rapid and continuous corrosion. Ans. Formation of volatile and porous oxide film cause rapid and continuous corrosion.----------------------------------------------------------------------------------------------------------------------------------Q.36. Formation of which type of metal oxide film prevent corrosion.Ans. The nonporous film of metal oxide film is prevent corrosion because the volume of metal oxide is greater then the metal. ----------------------------------------------------------------------------------------------------------------------------------Q.37. What is electrochemical corrosion. (Wet corrosion) The corrosion which is brought about through ionic reactions in the presence of moisture or solution as conducting medium when two dissimilar metals are in contact with each other. ----------------------------------------------------------------------------------------------------------------------------------Q 38. What is galvanic corrosion. Ans. When two dissimilar metals are electrically connected and exposed to electrolyte, the metal higher in electrochemical series undergo corrosion. Q.39. The rate of corrosion increases with increase in temperature. Ans. With increase of temperature of the environment, the rate of reaction as well as rate of diffusion increase, there by corrosion rate increases. ----------------------------------------------------------------------------------------------------------------------------------Q.40. Impure metals corrode faster than pure metal under identical conditions. Give reason. Ans Impurities in a metal generally cause heterogeneity and form minute electrochemical cells at the exposed parts, whereby the anodic parts get easily corroded. ----------------------------------------------------------------------------------------------------------------------------------Q.41 A steel screw in a brass marine hardware corrodes. Give reason.Ans. This is due to galvanic corrosion. Iron is higher in activity series than brass. So iron becomes anodic and is attached and corroded, while brass is in lower in series acts as cathode and gets protected. ----------------------------------------------------------------------------------------------------------------------------------Q.42. What is differential aeration corrosion?Ans. When one part of the metal is exposed to a different air concentration from the other part, then poorly oxygenated part become anodic and undergoes corrosion, while the highly oxygenated part becomes catholic and remains unaffected by corrosion. ----------------------------------------------------------------------------------------------------------------------------------Q.43. What is the effect of pH on corrosion. Ans. The lower the pH ( More acidic), greater is the corrosion. ----------------------------------------------------------------------------------------------------------------------------------Q.44. Rusting of iron is faster in saline water than in ordinary water, why?Ans. The presence of sodium chloride (NaCl) in water leads to increase the conductivity of solution in contact with iron surface, therefore rusting is speeded up. ----------------------------------------------------------------------------------------------------------------------------------Q.45. What is cathodic protection?Ans. It is a protection of parent metal from corrosion by connecting it with a more active metal (more anodic metal) like Mg, Al etc. The connected active metal undergoes corrosion, thereby protecting the parent metal from corrosion. ----------------------------------------------------------------------------------------------------------------------------------Q.46. What is the effect of carbon-dioxide on electrochemical corrosion.Ans. The corrosion is faster because CO2 gets dissolved in water producing an acidic electrolyte (H2CO3). The rate of corrosion is faster in acidic conditions.----------------------------------------------------------------------------------------------------------------------------------Q.47. Why does corrosion occur in steel pipe connected to copper plumbing?

Ans. When iron or steel pipe connected to copper plumbing is exposed to an electrolyte, then iron (the metal higher in electro chemical series) undergoes corrosion. Since iron forms an anode and is attacked and corroded. Whereas copper (lower in electro chemical series) acting as cathode is protected. This type of corrosion is called galvanic corrosion. ----------------------------------------------------------------------------------------------------------------------------------Q.48. Bolt and nut made of same metal is preferred in practice, why?Ans. Bolt and nut made of same metal is preferred, because such combination do not permit galvanic corrosion to take place. ----------------------------------------------------------------------------------------------------------------------------------

Sample Test Paper 1Subject: Applied Science (Chemistry) Marks: 25 Time: 1 hour

Q1. Attempt any four of the following. (8 Marks)a) Write four physical properties of copper.

b) State the purposes of roasting of copper ore.

c) Name the steps involved in extraction of aluminium from bauxite.

d) Define corrosion. Mention types of corrosion with one example of each.

e) Mention factors affecting electrochemical corrosion.

f) Why do metals corrode faster in Mumbai than in Pune?

Q2. Attempt any three of the following. (9 Marks)

a) Write chemical reactions for the action of air, water and dilute HCl on copper. b) How is metal protected from corrosion by sacrificial anodic protection?c) Write the composition, properties and applications of tinmann’s solder.d) Write mechanism of corrosion of metal due to action of oxygen.

d) Describe the process of sherardizing with the help of diagram.

Q3. Attempt any two of the following. (8 Marks)

e) Write Bessemerization process in extraction of copper with neat and labeled diagram.

f) Write four differences between galvanizing and tinning.

g) Describe the process of electrolytic reduction of alumina with neat and labeled diagram

--------------------------------------------------------------------------------------------------------------------------------------------------------------

Q1. Attempt any four of the following. (8 Marks)a) Define specific conductance and give its unit.

b) Write two limitations of fuel cells.

c) Write applications of glass in electronic industry.

d) Define electrically insulating polymers. Write two examples.

e) Write two properties and two applications of epoxy resin.

f) Write two properties and two applications of silicone fluids.

Q2. Attempt any three of the following. (9 Marks)a) Write three differences between Primary and secondary cells.

b) Explain construction of Dry cell with the help of diagram.

c) Define charging and discharging. Write one chemical reaction for each.

d) Define photoconductive polymers. Write two examples and two uses of them.

e) Write three properties and three uses of Bakelite. Q3. Attempt any two of the following. (8 Marks)

a) Describe construction and working of lead acid storage cell with diagram.

b) Write four advantages of hydrogen-oxygen fuel cell. c) Define electrically conducting polymers. Write four examples and two uses of it.

Course Name:Electronics & Computer Engineering Group

Course Code: EE/EP/EJ/EN/ET/EX/EV/IC/IE/IS/MU/DE/ED/EI/IU/CO/CM/IF/CD/CW Semester: II

Title of the Subject: Applied Science (Chemistry)

Subject Code: 17211

Marks: 50 Time:2Hrs.

Q1. Attempt any Nine (18)a) Name four ores of copper with their formulae.

b) Name the sequential steps involved in extraction of copper from its sulphide ore.

c) Write four properties of aluminium.

d) Name four factors affecting electrochemical corrosion.

e) Define metal cladding. Write its two applications.

f) Why galvanized containers are not used for storing food stuffs?

g) Define cell and battery.

h) Why do dry cells stop working after some time even though it is not in use?

i) Define cementation. Name two methods of cementation.

j) What do you understand by LCP? Write their two applications.

k) Differentiate between dielectrics and insulators.

l) Write four advantages of adhesives.

Q2. Attempt any four (16)a) Write the process of smelting of copper ore with labeled diagram.

b) Describe the concentration method of alumina by Bayer’s process.

c) Write composition and applications of -1) brazing alloy 2) Plumber’s solder.

d) Write two properties and two uses of teflon.

e) With the help of diagram and chemical reactions, describe hydrogen oxygen fuel cell.

f) Distinguish between electrolytic cells and electrochemical cells.

Q3. Attempt any four (16) a) By giving properties and examples, describe protective and non-protective oxide films.

b) Describe the mechanism of electrochemical corrosion by absorption of oxygen gas.

c) Distinguish between galvanizing and tinning.

d) Explain construction working of Ni- Cd cell.

e) Explain discharging and charging process of lead acid cell.

f) Write advantages and limitations of fuel cell.

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