01. Define Boiler Feed Water. What are the requirements of Boiler Feed Water?

Boiler Feed Water: The water fed into boiler for the production of steam is called

boiler feed water.

It should be free from turbidity, oil, dissolved gases, alkali and hardness

producing substances.

Requirements of Boiler Feed Water:

i). It should has zero hardness.

If hardness present in boiler feed water, it produces scales and sludges, which

prevents efficient heat transfer.

ii). It must free from dissolved gases like O2 and CO2.

If dissolved gases present in boiler feed water, it leads to boiler corrosion.

iii). It should be free from suspended impurities.

If it is present in boiler feed water, it produces wet steam.

iv). It should be free from dissolved salts and alkalinity.

If it is present in boiler feed water, it produces caustic embrittlement, which causes

brittlement of boiler parts.

Unit – I Water Technology.

02. What is Zeolite? How is water softened by zeolite? Give equations.

Zeolite:Sodium Aluminum Orthosilicate.

Na2O.Al2O3.xSiO2YH2O.

The synthetic form of zeolite is known as

PERMUTIT, which is porous and possess gel

structure and Ze stands for insoluble zeolite.

Principle: The sodium ions which are loosely held

in Na2Ze are replaced by Ca2+ and Mg2+ ions present

in water.

Process: When hard water is passed through a bed

of zeolite placed in a closed cylinder, the hardness

causing ions like Ca2+ and Mg2+ ions are taken up

by zeolite. Sodium salts are released during the

reaction as byproduct.

For softening of water by zeolite process, hard water is percolated at a specified rate through a bed

of zeolite, kept in a cylinder.

The hardness causing ions like Ca2+ and Mg2+are retained by the zeolite as CaZe and MgZe. While

the outgoing water contains sodium salts.

The various reactions taking place may be

Advantages: (i). Output water has only 1-2 ppm.

(ii). Operation is easy.

(iii). No sludge is formed during the process.

03. Explain formation of deposits in steam boilers and heat exchangers.

Steamboilers: Sealed vessel where water is converted to steam.

A steam boiler is a type of generator that is used to create steam.

Heat exchangers:A device for transferring heat from one medium to another.

Heat exchangers are designed to remove excess heat from aircraft

engines, optics, x-ray tubes, lasers, power supplies, military

equipment, and many other types of equipment that require cooling

beyond what air-cooled heat sinks can provide.

Formation of deposits: Scale and sludge formation.

Scale:If the precipitate forms hard and adherent coating on the inner walls of the boiler is known as

scale. It is formed by the substances like CaSO4, Mg(OH)2 and Ca(HCO3)2.

Scales are difficult to remove even with the help of hammer and chisel. Scales are the main

sources of boiler troubles.

Formation of scales may be due to

(i). Decomposition of calcium bicarbonate.

(ii). Deposition of calcium sulphate.

(iii). Hydrolysis of magnesium salts.

(iv). Presence of silica.

Sludge: In boiler, water contains the precipitate loose and slimy is known as sludge. It

is formed by the substances like CaCl2, MgCl2, MgSO4 and MgCO3.

Disadvantages:

(i). Poor conductor of heat.

(ii). Excessive sludge formation disturbs the working of the boiler.

(iii). It forms along with scales, then former gets entrapped in the latter and both get

deposited scales.

Prevention of sludge formation:

(i). By using well softened water.

(ii). By frequently below down opearation.

04. What are the disadvantages in scale formation? Explain in detail.

Or

What are the disadvantages formation of deposits in steam boilers and heat exchangers?

Or

Write short notes on (i). Wastage of fuels. (ii). Decrease in efficiency. (iii). Boiler Explosion.

Disadvantages: (i). Wastage of fuels.

(ii). Decrease in efficiency.

(iii). Boiler Explosion.

(i). Wastage of fuels:

(ii). Decrease in efficiency:

Scales may sometimes deposit in the valves and condensers of the boiler and choke then

partially. This results in decrease in efficiency of the boiler.

(iii). Boiler Explosion:

When thick scales crack due to uneven expansion, the water comes suddenly in contact

with over-heated iron plates. This causes in formation of a large amount of steam suddenly. So

sudden high-pressure is developed, which may even cause explosion of the boiler.

05. What are the disadvantages using hard water in boilers?

Disadvantages:

1. Scale and sludge formation. [seeQ.No: 3]

2. Priming and Foaming. [seeQ.No: 10]

3. Caustic Embrittlement. [seeQ.No: 7]

4. Boiler Corrosion. [seeQ.No: 9]

06. Explain prevention of scales formation.

Prevention of scales formation: (i). External Treatment.

(ii). Internal Treatment.

(i). External Treatment:Softening of water (i.e) removing hardness- producing constituents

of water. Ex: Zeolite process and Demineralization process.

(ii). Internal Treatment:Sequestration process.

An ion is prohibited to exhibit its original character by complexing or converting it into other

more soluble salt by adding suitable reagent.

An internal treatment – by adding proper chemical to the boiler water either

(a). To precipitate the scale forming impurities in the form of sludge, which can be remove by blow

–down operation (or)

(b). To convert them into compounds, which will stay in dissolved form in water and thus do

not cause any harm.

Blow down operation: It is partial removal of hard water through top at the bottom of boiler, when

extent of hardness in the boiler becomes alarmingly high.

Internal treatments methods are, generally, followed by blow-down operation , so that accumulated

sludge is removed.

Internal treatment methods are, (i). Colloidal Conditioning

(ii). Phosphate Conditioning

(iii). Carbonate Conditioning

(iv). CalgonConditioning.

07. Write short notes on Caustic Embrittlement.

It is a type of boiler corrosion, caused by using highly alkaline water in the boiler.

In boiler water, it contains a small amount of sodium Carbonate. In high pressure, it decomposes to

give sodium hydroxide.

2 3 2 2

Na CO +H O--- 2NaOH +CO

Then this NaOH reacts with boiler material and it forms sodium Ferrate and this leads to brittlement

of boiler parts like joints, bends etc.,

2 2 2

Fe+2NaOH--- Na FeO +H

It is prevented by or Avoided by

(i). By using sodium phosphate as softening reagent instead of sodium carbonate.

(ii). By adding Tannin or Lignin to boiler water for blocks hair-cracks.

(iii). By adding sodium sulphate to boiler water also blocks hair-cracks.

Caustic Embrittlement. = Intercrystalline cracking of boiler metal

Calgon=Sodium HexaMeta phosphate

Na2[Na4(PO3)6]

08. Explain Internal conditioning methods of softening hard water.

To remove hardness producing salts, chemicals were added to the boiler water in the boiler itself

and that treatment is called internal conditioning.

(i). Colloidal Conditioning (ii). Phosphate Conditioning

(iii). Carbonate Conditioning (iv). Calgon Conditioning.

(i) Colloidal Conditioning:

In low-pressure boilers, scale formation can be avoided by adding organic substances like

kerosene ,tannin, agar-agar (a gel), etc., which get coated over the scale forming precipitates,

thereby yielding non-sticky and loose deposits, which can easily be removed by pre-determined

blow-down operations.

(ii). Phosphate conditioning:

Three types of phosphates- mono, di and trisodium phosphates are employed in phosphate

conditioning. The advantages of phosphate conditioning over carborateconditioning are (i).It can be

applied to high pressure boilers and

(ii) It can be used for softening/ conditioning acidic, neutral or alkaline water sample.

2+

3 4 3 4 2Ca +2Na PO --- Ca (PO )

If acidic water is to be conditioned,trisodium phosphate can be used. For neutral and

alkaline water samples disodium phosphate and monosodium phosphate can be used respectively.

(iii) Carbonate conditioning:

In low pressure boilers, calcium ions are converted into soft and loose sludge by adding

sodium carbonate solution. It forms soft CaCO3 which can be removed by blow-down operation.

4 2 3 3 2 4

CaSO +Na CO --- CaCO Na SO

(iv). Calgon conditioning:

Calgon interacts with calcium ions forming a

highly soluble complex and it prevents the

precipitation of scale forming salt. The complexNa2[Na4(PO3)6] is soluble in water and no problem

for its sludge disposal.

4 2 4 3 2 2 3 2 46 62CaSO +Na Na PO --- Na Ca PO 2Na SO

09.Write short notes on Boiler corrosion / Explain boiler corrosion in detail /

Write short notes on Boiler troubles – Boiler corrosion.

Boiler corrosion taken place in boiler in the presence of gases like dissolved oxygen, dissolved

CO2 and dissolved salts.

Dissolved oxygen:It attacks the boiler material at high temperature and causes the

Corrosion.

2 2 3

4Fe+6H O+3O --- 4Fe(OH)

It is removed by chemical and mechanical method.

Chemical Method: Sodium sulphite, Hydrazine used to remove dissolved oxygen.

Mechanical Method: To remove by De-aeration method.

Water spraying in a perforated plate-fitted tower, heated from sides and

connected to vaccum pump. High temperature, low pressure and large

exposed surface reduces the dissolved oxygen in water.

Dissolved CO2: It produces carbonic acid, which is acidic and corrosive in nature

2 2 2 3

CO +H O--- H CO ( )Carbonic acid

It can be removed by adding calculated amount of NH4OH into water

and also removed by de-aeration method.

Dissolved salts(MgCl2):Salts like CaCl2 and MgCl2 undergoes hydrolysis at higher

temperature , to give HCl , which corrodes the boiler

2 2 2

2 2

2 2 2

MgCl + 2H O--- Mg(OH) +2HCl

Fe+2HCl --- FeCl + H

FeCl + 2H O---- Fe(OH) +2HCl

It can be avoided by adding alkali into the boiler water.

10. Explain priming and foaming (carry over).

1.Priming: It is the process of production of wet steam.

Wet steam – Steam contains droplets of liquid water

It is caused by

i) High steam velocity

ii) Very high level water in the boiler

iii) Sudden boiling of water

iv).Very poor boiler design.

Prevention: It is controlled by

1) Controlling the velocity of steam

2) Keeping the water level lower

3) Good boiler design

4) Using treated water

2) Foaming:

The formation of stable bubbles above the surface of water is called foaming These

bubbles are carried over by steam leading to excessive priming.

It is caused by

i) Presence of oil and grease

ii) Presence of finely divided particles.

It can be prevented by

i). Adding coagulants like sodium aluminate

ii).Adding anti-foaming agents like synthetic polyamides.

11. What is Desalination? Describe desalination of by Reverse Osmosis method with

neat diagram.

Or

Explain the reverse osmosis process for desalination of brackish water in detail.

Reverse Osmosis(RO):

When a pressure greater than osmotic pressure applied on the concentrated side, the solvent flow

takes place from higher concentration to lower concentration is known as reverse osmosis.

Process:

1) In this RO process, Pure water is separated from salt water.

2) This RO process is also known as Super filtration or Hyper filtration

3) When the pressure is applied from the higher concentration side, the solvent flow takes

place to lower side and these two concentrations are separated by semipermeable

membrane, the salt water is converted into pure water.

4) The membranes used as cellulose acetate, polyamide and some polymers.

Advantages & RO method:

1. Low capital cost, easy operating.

2. It is used for converting sea water into drinking water

3. It removes all types of impurities like non-ionic and colloidal

4. 4. The life time of membrane is high and it can be replaced within few minutes.

Desalination = Removal of common salt-NaCl from water.

Brackish water = Water containing dissolved salts with a peculiar salty taste. Ex: Sea water

12. Explain demineralization process in detail.

01. What is electrochemical cell? Explain with example of Daniel cell.

Electrochemical cell: Cells in which the e-s transferred due to redox reaction and

converted into electrical energy.

Example : Daniel cell.

Daniel cell consists of two electrodes like Zn and Cu.

Zinc electrode is dipped in 1M ZnSO4 solution and Cu electrode dipped in 1M CuSO4

solution.

The two solutions are inter connected by a salt bridge and two electrodes are connected

by a wire through the volt meter.

Each electrode is known as half-cell.

The e-s liberates from Zn electrode flow through the external wire and is consumed by

copper ions at the cathode.

Salt Bridge: U- tube containing saturated solution of KCl in agar-agar gel. It

Salt Bridge: U- tube containing saturated solution of KCl in agar-agar gel. It

connects two half cells.

Function of salt bridge: It eliminates liquid junction potential and electrical

continuity between two half cells.

CY6251, ENGG. CHEMISTRY-II / 16 MARKS Q &A

Unit – IiELECTROCHEMISTRY & CORROSION

02. How electrochemical cell is measured? How Emf is measured by

potentiometrically?

03. What are electrochemical series? Give its applications.

Electrochemical series: An arrangement in which the standard electrode reduction

potential of different metals are arranged in increasing order on the basis of

hydrogen scale is known as emf series.

Applications of EMF series: (i). To calculate the std. emf of a cell.

(ii). Relative ease of oxidation or reduction.

(iii). Displacement of one element by other.

(iv). To determine K of a reaction.

(v). Hydrogen displacement from acid solutions.

(vi). Predicting spontaneity of redox reations.

(i). To calculate the std. emf of a cell.

The emf of a cell is calculated as follows, Ecell= ER-EL

(ii). Relative ease of oxidation or reduction.

+ve value – higher reduction potential – high reduction.

F- = 2.87, higher reduction – get oxidized

Li+ = -3.07, lower reduction – high oxidation.

(iii). Displacement of one element by other.

Metals which lie higher in the series can displace those elements which lie below them in

the series. Cu can easily displaced by Zn

(iv). Determination of Equilibrium Constant K of a reaction.

From the value of Eo, we can be determined the equilibrium constant K

(v) Hydrogen displacement Behavior

Metals with above H2 scale will displace the hydrogen from an acid solution (ie)-ve

reduction potential. Zinc reacts with hydrogen but not in Ag. Why?

Because it has positive reduction potential

(vi) Predicting Spontaneity of Redox Reactions:

Eovalue is positive=Reaction is Spontaneous

Eovalue is –ve =Non-Spontaneous Process.

04. Derive Nernst equation.

Applications:

(i) To calculate electrode potential of unknown metal (ii) Application of emf series

(iii) Corrosion tendency of methods can be predicted

05. What is Chemical corrosion? Explain with its types.

It is classified into 3 types. i). Oxidation corrosion.

ii).Corrosion by the other gases – Hydrogen

iii).Liquid – Metal corrosion

01. Oxidation corrosion

Oxygen present in atmosphere attacks metal surface resulting in the formation of metallic oxide

which is a corrosion product and known as oxidation corrosion.

Oxidation occurs first at the surface of the metal and the resulting metal oxide scale forms a

barrier that tends to restrict either further oxidation. For oxidation to continue either the metal must

diffuse outwards through the scale to the surface or the oxygen must diffuse inwards through the

scale, to the underlying metal.

Both transfer occurs, but the outward metal diffusion is generally, much more rapid than the

inward diffusion of oxygen. Since the metal ion is appreciably smaller than the oxygen ion and

consequently of much higher mobility.

02. PILLING – BEDWORTH RULE:

The ratio of the volume of the oxide formed to the volume of the metal consumed is pilling

bed worth rule.

03. Corrosion by other gases – Hydrogen.

i) At ordinary Temperature : Hydrogen Embrittlement.

The process of formation of cracks and blisters on the metal surface, due to high pressure of

hydrogen gas is called hydrogen embrittlement

(i) Metal direct contact with H2s and forms atomic hydrogen

(ii) Atomic hydrogen diffuses readily into metal to form molecular hydrogen

2) At high temperature – Decarburization

The process of decrease in carbon content in steel is termed as decarburization of steel.

04) Liquid – metal corrosion

This is due to the chemical action of following liquid metal at high temperature.

The corrosion reaction involves

(i) Either dissolution of a solid metal by a liquid metal.

(ii) Liquid metal may penetrate into the solid metal.

06. Explain Electrochemical corrosion with its types.

01. Galvanic corrosion:

The corrosion occurs when two different metals are in contact with each other in presence of

an aqueous electrolyte solution or moisture is known as Galvanic corrosion.

The more active metal acts an anode the less active and metal acts as a cathode

In Zn-Fe bimetallic couple, Zn undergoes to

corrosion, because compare with Fe, it has

higher –Veemf Value. So it acts as an anode.

Iron acts as cathode and it is protected.

But in the case of Fe – copper bimetallic couple

Fe dissolves and copper is protected.

(ie) Fe acts an anode and copper as a cathode.

Prevention of Galvanic corrosion:

To prevent Galvanic corrosion, the bolt and but

are made by same metal. If they are n’t

corrosion will take place easily.

It may be minimized by putting an insulating material between the two metals.

02. Differential aeration corrosion:-Otherwise it is known as concentration cell corrosion.

It is due to the formation of concentration cell formed by the variation of concentration mainly of

oxygen or any electrolyte on the surface of the base metal.

i).When a metal is partially immersed in a solution, the

metal inside the solution has very poor aeration

compared with the metal that is outside the solution.

ii).The difference in the air concentration of the base

metal can produce the anode with less aerated area and

cathode.

iii).Corrosion will take place at the anode area where the

metal is converted into metal ion.

Example: A zinc metal partially dipped ina brackish

solution.

Example: Pitting Corrosion - The holes are formed at corrosion in concentrated places.

Low oxygen part= anode ,More oxygen part=cathode.

It is a localized attack, resulting in the formation of a hole around which the metal is relatively

unattached.Ex: metal area covered by a drop of water, sand, dust, etc.

07. Distinguish between Chemical corrosion and Electrochemical corrosion.

Chemical corrosion Electrochemical corrosion

1) It occurs dry state Wet state (i.e) presence in moisture

2) Local attack to metal by environment Large number of cathodic and anodic areas

3) Homogeneous metal surface gets

corroded

Heterogeneous surface

(i.e) Bimetallic contact.

4) Corrosion products accumulate in the

same place, where corrosion occurs

Corrosion occurs at the anode, while the

products formed else where

5) Chemical corrosion is self-controlled It is continuous process

6) It follows adsorption mechanism It follows electrochemical reaction

7) Ex: formation of mild scale on iron surface Ex: rusting of iron in moisture

8) 3 types. i). Oxidation corrosion

ii). Corrosion by other gases- H2

iii). Liquid – Metal corrosion.

2 types.

i). Galvanic corrosion.

ii). Differential aeration corrosion.

08. What are the factors influencing corrosion?

The rate of corrosion is mainly depends on

i) Nature of the metal

ii) Nature of the environment

i). Nature of the metal

a). Position in emf series: Metals above hydrogen in emf series, corroded easily.

Metals have high –ve reduction potential undergoes corrosion.

b) Relative areas of the anode and cathode: Rate of the corrosion has higher % in anodic area, the

rate of corrosion will be more, when the cathodic area is larger.

c) Purity of the metal: The 100% pure will not undergo any type of corrosion.

If impurity present in higher percentage, corrosion takes places at anode.

d) Over voltage:Corrosive environment is inversely proportional to corrosion rate.

e) Nature of the surface film: It is known as pilling- bed worth rule.

f) Nature of the corrosion product:Corrosion is faster when the corrosion product is soluble in

corroding medium. If the corrosion product is volatile, the corrosion rate will be faster.

ii). Nature of the environment:

i). Temperature: Rate of corrosion α temperature.

The rate of corrosion increase with temperature

ii). Humidity: If the humidity is high in the environment, corrosion will be more.

iii). Presence of corrosive gases: The acidic gases like CO2,SO2,H2S are produce electrolytes,

which are acidic and increases the electrochemical corrosion.

iv). Presence of suspended particles: Particles like NaCl present in the moisture and acts a

powerful electrolyte and then enhance the electrochemical corrosion.

v). Effect of pH; the rate of corrosion will be maximum when the corrosive environment is acidic

(ie) PH<7.

09. Explain the Sacrificial anode and impressed current techniques for the preventions

ofcorrosion.

i) Sacrificial anode method:

i). The application of sacrificial anodes in cathodic protection is based on the differences in

electrochemical reactivity of metals.

ii). In this method, the metal to be protected from corrosion is connected to more activemetal

which acts as an anode.

iii). In a redox reaction involving iron and zinc, the zinc will serve as the anode, and iron the

cathode.

iv). The zinc anode will oxidize and provide electrons for the reduction of Fe2+ to elemental

iron.

v).This is called cathodic protection. The zinc anode is termed a sacrificial anode.

vi). Iron pipes buried in the ground, and designed to carry water, would normally be expected

to rust pretty quickly.

vii).If they are buried along with a piece of zinc, and connected by a wire the zinc will provide

cathodic protection.

2. Corrosion control through Impressed current method:

An alternative method of providing the current to protect a system is to use some sort of

external power supply. As with the sacrificial system , the structure to be protected is made the

cathode, the difference being that the driving force. Behind the current is not the difference in

potential between the anode and cathode of the system but from the power supply.

Both these types of cathodic protection may be applied to buried pipelines and to steel

hulled ships. For oil drilling platforms, however the method employed is sacrificial in the vast

majority of cases in the north sea.

This technique is useful for protecting large structures like water tanks, underground oil

collers, laid up ships,etc.

10. What is paint? What are the constituents and their functions in paint?

Paint: paint is a mechanical dispersion of one or more finely divided pigments in a medium (thinner

+ vehicle) . When paint is applied to a metal surface, the thinner evaporates, while the vehicle

undergoes slow oxidation forming a pigmented film.

Constituents:

1. Pigments. 2. Vehicle or drying oil. 3. Thinner. 4. Drier. 5. Filler or extender. 6. Plasticizer

7. Antiskinnig agent.

i) Pigments: They are colour producing substances in paint.

Ex: white colour- white lead, black=- carben black red-indian red, green –chromium

oxide.

Function: i). It gives colour and opacity to the film.

ii). It also provides strength to the film.

iii). It provides weather resistance of the film.

ii) Vehicle (or) drying oil:This is a non-volatile portion of a medium and film forming constituent of

the paint. These are high molecular weight fatty acids present in vegetable and animal oils. Ex:

Linseed oil, castor oil.

Function:

i) They form a protective film by the oxidation and polymerization of the oil

ii) They hold the pigment particles together on the metal surface

iii) They impart water repellency , toughness and durability to the film.

iii) Thinners or solvents: Thinner is a volatile substance present in the medium.

Ex: turpentine, toluol, xylol etc.

Function:

I) It increases the elasticity of the film

II) It helps easy drying of the paint film

III) It increases the penetrating power of the vehicle.

iv) Extenders or fillers: These are colourless (white) pigments which improve the quality of the

paint. Ex: Gypsum, Jal ,china clay, silica, etc.

Functions:

i) It reduces the cost of paint

ii) It prevents the cracking and shrinkage of the film

iii) It modifies the shades of the pigments

v).Driers: these are the substances, used to accelerate the process of crying.

Ex: metallic soaps.

Functions: i).They are oxygen –carriers (or) catalists.

ii). They provide oxygen , which is essential for oxidation, polymerization of drying oil.

vi).Plasticisers: these are chemicals added to the paint to provide elasticity to the film and to

prevent cracking of the film. Ex: triphenyl phosphate, tricresyl phosphate, etc.

vii). Antiskinning agents:These are chemicals added to the paint to prevent gelling and skinning of

the paint. Ex: polyhydhroxy phenol.

11. Explain the electroplating of Gold.

Electroplating: It’s a process in which the coating metal is deposited on the base metal by passing

a direct current through an electrolytic solution containing the soluble salt of the coating metal.

Ex: Electroplating of Au (gold) over copper object.

The copper object to be plated is first treated with dilute acid.

Then this copper object and gold rod are immersed in an electrolyte.

Copper object acts cathode and gold rod is an anode.

These electrodes are connected with direct power supply.

When current is passed from battery through the solution, gold dissolves in electrolyte and deposits

uniformly in copper object.

12. Explain the Electroless plating of Nickel.

Definition: it is a technique of depositing of a noble metal from its salt solution on a catalytically

active surface of a base metal by using a suitable reducing agent.

Electroless Nickel plating:

Step 1: Pretreatment and activation of the surface:

The surface to be plated is first degreased by using organic solvents or alkali followed by acid

treatment.

Step 2: preparation of plating bath composition:

Coating solution NiCl2.6H2O 30 g/l

Reducing agent NaH2PO2H2O (sodium hypophosphite)

10 g/l

Complexing agent Sodium succinate 10 g/l

Buffer Sodium acetate 10 g/l

Temp 85-95oc

pH 4-6

The pretreated object is immersed in the plating bath for the required time during which the

following reduction reaction will occur and the Ni gets coated over the object.

Metal ions + Reducing Agent Metal (Deposited) + Oxidised Product

01. Distinguish between Nuclear fission and Nuclear fusion reaction.

Nuclear fission Nuclear fusion

1. Breaking a heavy nucleus into smaller Combination of two smaller nuclei.

2. Emits radioactive rays Does not emit radioactive rays

3. Reaction takes place at ordinary temperature

At high temperature. > 106K.

4. It gives chain reaction. No chain reaction

5. Emits neutron Emits positron

6. It can be controlled It cannot be controlled.

7. The mass number and atomic number of new elements are lower than the parent nucleus.

Higher than that of starting elements.

8. Ex: Fission reaction of 92U235, power

generation in Nuclear Power Plant, Kalpakkam&koodankulam, Tamilnadu.

Ex: Fission reaction takes place in sun.

CY6251, ENGG. CHEMISTRY-II / 16 MARKS Q &A

Unit – Iii energy sources.

02. Define Nuclear fission reaction. Explain with one example in detail.

03. Explain Nuclear Reactor-Power Generator with neat diagram./ Light Water Reactor

Nuclear Reactor: A device used for power generation, in which a nuclear chain reaction

is initiated, maintained and controlled to produce the heat energy is

known as nuclear reactor

.

Converted Converted

Components:

1) Fuel Rods: It produces heat energy and neutrons.

Ex: Natural Uranium (99.28% U238 and 0.714 % U235) and Pu239

2) Control Rods: To keep power production at a steady state.

Ex: Boron and Cadmium rods.

3) Moderators: Function to reduce the kinetic energy of fast fission neutrons to slow neutron

and this is done in a small fraction of a second.

Ex: Graphite, Be, Ordinary water and Heavy water.

4) Coolants: To remove the intense heat produced in the reactor and to bring it out for

utilization. Ex: Ordinary water, Heavy water, liquid metals and gases.

5) Reflector: It placed around the core to reflect back some of the neutrons that leak out

from the surface of the core.

6) Pressure vessel: It enclosed the core and reflector. It also provides the entrance and exit

passages for coolant. (Pressure 200 kg/cm2)

7) Shielding: To attentiate the Gama rays and other radiations coming out from the reactor.

2 Types. (i). Thermal shield (ii). Biological shield.

8) Turbine: The steam at high pressure, generated in the heat exchanger is used to

operate a steam turbine, which derives a generator to produce electricity.

Nuclear Energy

Thermal Energy

(or)

Heat Energy

Electrical Energy

04. Explain Breeder reactor with reactions.

05. Define solar cell. Explain solar energy conversion in detail.

Solar cell = Photogalvaniccell : It is a device used for converting solar energy into electricity. It is

made by interconnecting a large number of photovoltaic cells.

Solar Energy Conversion: It is the process of conversion of direct sunlight into more useful forms.

Conversion may be in two forms. 1. Thermal Conversion. 2. Photo Conversion.

01. Thermal Conversion:

It involves absorption of thermal energy in the form of IR radiation. Temperature below

100oC, is useful for heating purpose of water and refrigeration.

Methods: (i).Solar heat collectors. (ii).Solar water heater.

(i). Solar heat collectors: It consists of natural materials like stones, bricks which can absorb

heat during the day time and release it slowly at night.

Uses: It is used for houses in cold condition.

(ii). Solar Water Heater:

It consists of an insulated box inside of which is

painted with black paint. There is a provision for sun light

absorption using a glass lid and store solar heat. Inside the

black painted, copper coil and cold water is flow in and gets

heated and storage in a tank.

02. Photo Conversion: It involves conversion of light energy directly into electrical energy.

Methods: Solar Cell.

Solar Cell: Ex: Solar light, solar pump, solar battery.

It is a device, converting solar energy directly into

electrical energy.

Principle: When solar rays fall on a two layer of

semi-conductor devices, a potential difference between the two layers is produced. This potential

difference causes flow of electrons and produces electricity.

Working: When the solar ray falls on the top layer and the e-s promoted to the conduction into n-

type semiconductor. The potential difference occurs; it should lead current increasing (i.e) flow e-s.

They are connected with an external circuit, and current is generated.

Applications of Solar Energy :(i). Used in calculators,Watches, etc.

(ii). Used to drive Vehicles.

(iii). Used in boilers to produce hot water for domestic and Industrial uses.

(iv). Used for lighting purposes. (v). Used as a source power in space crafts and satellites. (vi).

Used for producing hydrogen by hydrolysis of H2O.

Demerits of Solar Energy: (i). Huge capital cost.

(ii). Not available during night and cloudy days. (iii). Storage of energy is not possible.

06. Write a short note on Wind Energy.

Moving energy is called Wind.

Energy recovered from the force of the wind is called wind energy.

The wind energy is harnessed by making use of wind mills.

01.Wind Mills:

The strikes of blowing wind on blades of the

wind mill make it rotating continuously. The

rotational motion of the blade drives a number of

machines like water pump, flour mills and electric

generators.

Wind mills are capable of generating about 100 kw

electricity.

02. Wind Farms.

It is known as the large number of joining wind mills called wind farm. It produces a large amount of

electricity.

The minimum speed required for working of a wind generator is 15 km/hr

03. Other methods: (i). Sky Sail (ii). Ladder mill.

Advantages/ Merits of Wind energy:

i. It does not cause any Air pollution.

ii. It is very cheap and economic.

iii. It is renewable.

Disadvantages of Wind energy:

i. It produces noise.

ii. It produces unwanted sound.

iii. Affects bird’s life.

iv. Affected to the radio signals.

07. Define Battery. Explain with its types.

Battery:

It is a device, converted chemical energy into electrical energy. It contains

several anodes and cathodes.

It is an arrangement of several electrochemical cells connected in series and it

can be used as a source of direct electric current. (D.C).

TYPES OF BATTERIES:

01. PRIMARY BATTERY

i. It is known as Non-Reversible battery.

ii. Electrode and electrode reactions cannot be reversed by passing an external current.

iii. Reactions take place only once and after use they become dead.

iv. They are not chargeable.

v. Ex: Dry Cell, Mercury Cell, Leclanche’s cell.

02. SECONDARY BATTERY

i. It is known as Reversible battery.

ii. Electrode and electrode reactions are reversiblewhen an external current is passing

iii. It can be recharged again and again.

iv. Also called as Storage cells or Accumulators.

v. Ex: Lead-Acid Battery, Ni-Cd.

03. FLOW BATTERY

In these cells, the reactants, products and electrolytes and continuously passing through the

cell. Here chemical energy is converted to electrical energy.

Ex: H2-O2 fuel cell.

08. Explain Alkaline Battery with neat diagram and cell reactions.

Alkaline battery consists of electrolyte KOH and a Zinc cylinder filled with powdered Zn, KOH and

MnO2 in the form of paste using starch and water. A carbon rod [Graphite] acts as a cathode and it

is immersed in the electrolyte in the centre of the cell. The outside cylindrical zinc body acts as an

anode.

- -

2

- -

2 2 2 3

2 2 2 2

At Anode : Zn+2OH --- Zn(OH) + 2e

At Cathode : 2MnO +H O+2e --- Mn O +2OH

-----------------------------------------------------------------------------Overall : Zn+2MnO +H O --- Zn(OH) +Mn O

3-----------------------------------------------------------------------------

Advantages:

i. Zinc doesn’t dissolve in a basic medium.

ii. Its life is longer than dry battery because there is no corrosion on Zn.

iii. It maintains its voltage, when the current is drawn from it.

Uses:

It is used in calculators and watches.

Anode Zinc body

Cathode Carbon rod / Graphite rod

Electrolyte Powdered KOH, MnO2 in the form of paste.

09. Explain Lead acid storage battery.

Cell Representation:

This is also a rechargeable battery.

It consists of number of voltaic cells. In each cell, anode is Pb plate and cathode is PbO2

A known number of lead plates are connected with parallel and a number of PbO2 plates

and also connected in parallel. Various plates are separated by insulators like glass fibre. The total

anodes and cathodes are immersed in dil.H2(SO)4 Solution.

Cell reactions: Discharging.

2 -

(S) 4 4

2 -

2(S) 4 4( ) 2

(S) 2(S) 2 4( ) 4( ) 2

At Anode : Pb +SO PbSO + 2e

At Cathode : PbO +4H + SO 2e PbSO +2H O

Overall : Pb PbO 2H SO 2PbSO 2H O Ener

S

aq S

gy

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

Advantages:

(i). It is made easily. (ii). It produces very high current.

(iii). Effective one at low temperature. (iv). Self- discharging rate is low.

Uses:

(i). Used in automobiles like Car, Bus, Van, Lorry, Bike etc.

(ii). Used in Hospitals, Power stations, Telephone exchanges etc.

Anode Lead - Pb

Cathode Lead Oxide PbO2

Electrolyte Sulphuric acid - H2(SO)4

Pb/Pb(SO)4//H2(SO)4(aq)/PbO2/Pb

10. Explain Nickel – Cadmium battery with cell reactions.

Cell Representation:

This is also a rechargeable battery.

It consists of Cd anode and a metal grid containing a paste of NiO2 acts as a cathode. The

electrolyte is KOH.

Discharging: When Ni-Cd battery operates, Cd gets oxidation and forms Cd2+ and insoluble

Cd(OH)2 is formed. Its emf value is 1.4 V.

discharging- -

(S) 2charging

discharging- -

2(S) 2 2charging

Cell Reaction:

At Anode : Cd +2OH Cd(OH) +2e

At Cathode : NiO +2H O+2e Ni(OH) +2OH

discharging

(S) 2(S) 2 2 2chargingOverall : Cd NiO 2H O Cd(OH) Ni(OH) Energy-----------------------------------------------------------------------------------------------

Recharging: When an current is passed opposite direction, the cell reaction is reversed. As a

result, Cd gets deposited on anode and NiO2 on cathode.

Charging

2 2 (S) 2(S) 2DischargingCd(OH) Ni(OH) Energy Cd NiO 2H O

Advantages:

(i). It is smaller and lighter.

(ii). It has longer life than lead storage cell.

Uses:

(i). It is used in calculators, Electronic devices.

(ii). Used in transistors, cordless appliances.

Anode Cadmium (Cd)

Cathode A metal grid containing a paste of NiO2

Electrolyte KOH

Cd/Cd(OH)2//KOH(aq)/NiO2/Ni

11. Explain Lithium batteries in detail.

It is known as solid state battery because the electrolyte is used here at solid state.

Anode : Li(S) Li+ + e-

Cathode: TiS2 (S) + e- -

2TiS

Over all Li(S) + TiS2 (S) Li++ -

2TiS LiTiS2

Discharging:

When the anode is connected to cathode, Li+ ions move from anode to cathode.

Anode is Li and cathode is TiS2 and the electrolyte is solid polymer. The cathode is a material

capable of receiving the Lithium ions and electrons.

Recharging:

LiTiS2 Li+ + -

2TiS

It is recharged by applying an external current. Emf of Li cells = 3.0V.

Advantages: (i). Itsemf is high 3.0V.

(ii). It is a light weight material only 7g required for produce 1 mole of e-s.

Anode Lithium (Li)

Cathode TiS2

Electrolyte Polymer

12. Explain Hydrogen- Oxygen Fuel cell / [H2 – O2] Fuel cell.

Fuel Cell: It is a device in which the chemical energy of the fuel hydrogen is directly

converted into electricity without combustion.

Two porous electrodes – Made of compressed

carbon containing a catalyst like pt / pd.

It consists of two porous electrodes anode and

cathode. In between two electrodes an electrolytic solution

25% KOH or NaOH filled.

When H2 is bubbled through the anode

compartment, where it is oxidized. The O2 is bubbled at the

cathode compartment where it is reduced.

- -

2 2

- -

2 2

2 2 2

At Anode : H +2OH --- 2H O+ 2e

1At Cathode : O +H O+2e --- 2OH

2----------------------------------------------------------------------

1Overall : H O --- H O

2-------------------------------

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

The emf of the cell = 0.8 to 1.0 V.

Merits:

i. High efficiency.

ii. No unwanted noise and less maintenance.

iii. No pollution

iv. No need to change electrode often.

Uses:

i. Used in military vehicles and space vehicles.

ii. H2 – O2 fuel cell, the product is water, so no need of fuel because fuel is water.

Anode Hydrogen

Cathode Oxygen ( oxidizer)

Electrolyte 25% KOH or NaOH

01. What are Abrasives? Explain with classification.

Abrasives are hard substances used for Grinding, cutting, Shaping, drilling,

poslishingandsharpening operations.

Ex: Diamond,Talc

Moh’s scale of hardness:

It is a scale, in which common abrasives are arranged in the order of their increasing hardness.In

this scale, Lowest hardness substances is talc and noted 1

Highest hardness substance is diamond and noted 10

Classification of Abrasives:

CY6251, ENGG. CHEMISTRY-II / 2 MARKS Q &A

Unit – Iv, engineering materials

Property of an Abrasive = Hardness

02. Write short notes on (i). Grinding Wheel (ii).Abrasive paper and cloth.

(i). Grinding Wheel : It is manufactured by mixing abrasive grains with binder. The mixture

ismoulded and heated and cured.

Uses: It is used for the removal of scales from iron surfaces, cutting

tool sharpening.

(ii). Abrasive paper and cloth: The role of paper or cloth is made to pass through a series of

rollers and a thin coating of glue is applied on its upper side.

It is then passed then under a hopper from which the grit of

abrasive is allowed to fall and spread evenly on the glued

paper or cloth. Then it is dried in warm drying room. Finally it

is allowed to age for few days so that the glue sets firmly.

Uses: It is used to prepare smooth wood, metal and plastic surfaces.

03. Define refractories. What are its characteristics? Explain with classification and

itsproperties.

Refractories: Refractories are materials that can withstand very high temperature without

softening or decomposition in shape.

iii). Neutral Refractories:

i). They are neutral substances.

ii). They are made from weakly acidic and weakly basic materials.

iii). They are not attacked by both acidic and basic materials.

Example: Chromite, Graphite ,carborundum.

Properties : Refractoriness, RUL, Dimensional stability, Thermal spalling,

Thermal expansion , porosity.

04. Explain the properties of refractories.

Properties : Refractoriness, RUL, Dimensional stability, Thermal spalling,

Thermal expansion , porosity.

01. Refractoriness:

1. It is ability of a refractory material to withstand very high temperature without softening or

deformation under the working conditions

2. It is measured by PCE test.

3. PCE= Pyrometric cone equivalent

4. P.C.E number and softening temperature of some refractories are as follows

a. Silica bricks

b. Alumina bricks

c. Magnesite bricks

5. PCE is the number which refer to the softening temperature of a refractory specimen

of standard dimension 38mm height and 19mm triangular base.

Measurement:

5) This measurement is called segarcone test.

6) A test cone is determined by comparing its softening

temperature with softening temps.of a series of

standard pyrometric cones.

7) A test cone is prepared from the sample refactory

then it is placed along with the standard segar cone in an electric furnace and

heated at a rate of 10oC per minute.

8) The temperature at which apex (top) of the cone touches the base is taken as the

softening temperature .the PCE number of the standard cone which behaves

identically is taken as the PCE of the test sample.

2)RUL: Refractoriness Under Load:

The temperature at which the refractory deforms by 10 % is called refractoriness under

load. (i.e). The load bearing capacity of a refractory can be measured by RUL test.

A good refractory should have high RUL value.

RUL TEST:

RUL test is conducted by applying a constant load of 3.5 or 1.75 kg/cm2 to the test refractory

specimen of size base 5 cm2 and height 75 cm and heating in a furnace at a standard rate of 10oC

per minute.

03.Porosity: It is defined as the ratio of its por volume to the bulk volume

If porosity of a refractory is lower

i) posseses lower thermal conductivity

ii) it reduces thermal spalling

If porosity of a refactory is high

i). it reduces the strength

ii) .It reduces resistance to abrasion

iii). It reduces the resistance to corrosion

Porosity is used to determine like strength, corrosion and thermal conductivity.

A good refractory should have low porosity.

.

05. How Alumina, Magnesite and Silicon carbide are manufactured?

Manufacture of Alumina bricks:

Alumina bricks is an example for acidic refractories.

Alumina bricks are prepared from minerals silimanite and kyanite

They are anhydrous aluminosilicate materials Al2O3.SiO2

This mineral is fixed with coal in the ratio 1:1 along with plastic clay as binders.

The raw materials are mixed and moulded into bricks

The bricks are then dried and fired at 1600oc

The final product material contains 63 % alumina and 34% silica approximately.

These are used in steel industries.

Manufacture of Magnesite bricks:

Magnesite bricks are an example for basic refractories

Powdered caleinedmagnoite (Mgo) is mixed with caustic magnesia or iron oxide, as a

birder with water mixed and moulded into bricks.

The bricks are then dried and fired at 1500oC

The final product material containsMgO=85%,CaO=2.5% & SiO2=5.5%

There are used in open hearth furnaces, libing converters and reverberatory furnaces.

Manufacture of Silicon carbide (SiC): CARBORUNDUM

SiC is an example for very hard synthetic abrasive.

It is a mixture of SiO2 and coke.

Its hardness is 9.8 on Moh’s scale.

It is chemically inert and can withstand high temperature.

Preparation Or Manufacture:

It is prepared by heating a mixture of 60% sand (i.e) SiO2 and 40% coke with a small

amount of saw dust and a little salt in an electric furnace to about 1650oC for 36 hours.

2

SiO + 3C SiC + 2CO

Uses: used as heating elements in electric furnaces. Walls of chambers, kilns, coke ovens

and muffle furnaces. Used for grinding low tensile strength materials like cast iron, brass

etc.,

06. How Portland cement is manufactured?

It is manufacture by as follows

1. Mixing of Raw materials.

2. Burning.

3. Grinding.

4. Storage and Packing.

1. Mixing of Raw materials: It can be done by (i). Dry Process (ii). Wet Process.

(i). Dry Process: “ Silos” – limestone + clay > crushed and powdered – Dry raw mix.

(ii). Wet Process: Silos + Wet clay > Grinding mills > paste known as slurry.

2. Burning: Dry raw mix / slurry is carried out in rotary kiln.

The Dry raw mix / slurry is fed into the kiln from upper end and the flame is forced into the lower

end. Due to slope and slow rotation, the material gradually descends in the klin into different zones

of increasing temperatures.

(i). Drying Zone: Upper part of the kiln - About 400oc, water in slurry gets evaporated.

(ii). Calcination zone: Center part of the kiln - About 1000oc, limestone gets decomposed

intoCaO and CO2. 3 2CaCO ----- CaO + CO

(iii). Clinkering Zone: Lowest part of the kiln - About 1350-1500oc, limestone reacts with

clay to form Bogue compounds. C2S,C3S,C3A,C4AF.

The Bogue compounds fuse together to form small, hard, grayish

coloured stone like mass called cement clinkers.

3. Grinding : The hot clinkers are cooled with atmospheric air and then pulverized together

with 2-3% gypsum in ball mills. Gypsum act as retarding agent for quick setting

cement.

4. Storage and Packing: The cement coming out of the grinding mill is stored in a concrete

storage silos. Then the cement is packed in jute bags by automatic

machine.

07. Explain the properties of Portland cement.

Properties: (i). Setting and Hardening of cement. (ii). Heat of Hydration.

(i). Setting and Hardening of cement.

Setting: It is defined as the stiffening of the original plastic mass, due to the formation of

tobermonite gel.

Hardening: It is defined as the development of strength due to formation of crystals.

When cement is mixed with water, results formation of gel and crystalline products.

Chemical reactions:

(i). Flash set – When cement is mixed with water, hydration of C3A takes place and the paste

becomes quite rigid within a short time.(1 Day)

3 2 3 2

C A + 6H O C A.6H O

(II). Formation of Tobermonite gel: After the hydration of C3A, C3S begins to hydrate to give

Tobermonite gel and crystalline Ca(OH)2. This is responsible for the development of initial strength

of cement. The hydration of C3S gets completed within 7 days. It does not contribute much to the

strength of cement.

3 2 3 2 2 2

C S + 6H O C S .3H O +3Ca(OH)

(III). Dicalcium silicate (C2S) reacts with water very slowly and gets completed in 7 to 28 days.

2 2 3 2 2 2

2C S + 4H O C S .3H O +Ca(OH)

The increase in strength between 7 to 28 days is due to the formation of tobermonite gel and

crystalline Ca(OH)2.

(iv). The hydration of C4AF takes place initially, the hardening takes place finally through

crystallization along with C2S.

4 2 3 2

C AF + 7H O C A.6H O

Thus the final setting and hardening of cement is due to the formation of tobermonite gel plus

crystallization of Ca(OH)2 and hydrated tricalcium aluminate.

(ii). Heat of Hydration:

When water is mixed with

Portland cement some amount of

heat is liberated due to hydration and

hydrolysis reactions of Bogue

compounds. The average quantity of

heat is liberated is 500 kJ/kg.

08. Write short notes on special cements like waterproof and white cement.

(i). Waterproof cement:

It is obtained by adding water- proof materials like calcium stearate, aluminium stearate and

gypsum with tannic acid to ordinary Portland cement during grinding.

Functions: (i). To make concrete impervious to water under pressure.

(ii). To resist the absorption of water.

Properties:

(i). It is more expensive than ordinary Portland cement.

(ii). It act as pore-blocking and water- repelling agent.

Uses:

(i). Used in the construction bridges and structures under water.

(ii). White Cement:

It is white in color due to absence of iron compounds.

Such cements are made from raw materials which are free from iron oxide.

Properties:

(i). It is more expensive than ordinary Portland cement.

(ii). It act as pore-blocking and water- repelling agent.

Uses:

(i). Repairing and joining marble pillars and blocks, manufacture of tiles and mosaic

works.

(ii). Used in the construction bridges and structures under water.

09. Explain the manufacture the glass.

Raw materials:

a) Sodium is soda , Na2CO3 – Soft glass.

b) Potassium is potash, K2CO3 – Hard glass.

c) Calcium are limestone, chalk and lime

d) Lead are litharge, and red lead – Flint glass

e) Silica are quartz, white sand.

f) Zinc is zinc oxide – Heat and shock proof glass

g) Borate are borax , and boric acid - Heat and shock proof glass

h) Cutlets or pieces of broken glass to increase the fusibility.

4 steps.Involved in the manufacture.

1. Melting: The raw materials in proper proportions are mixed and finely powdered. This mixture

called batch is fused with some broken glass, called cullet in the pot of the tank furnace, in which

heating is done by burning produces gas and air mixture over the charge.

Heating is continued, till the molten mass is free from bubbles and glass-balls, and then cooled to

about 800oC.

2. Foaming and shaping:

Molten glass is then worked into articles of desires shapes by either blowing or moulding or

pressing between rollers.

3. Annealing:

Glass articles are then allowed to cool gradually to room temperature( sudden cooling must

be avoided, because cracking occurs ). The longer the annealing period, the better quality of glass.

4. Finishing:

All glass articles after annealing are subjected to finsish processes such as cleaning,

grinding, polishing, cutting etc.

10. Explain the types and properties and uses of glass.

1) . Soda lime or soft glass:

Raw materials: silica, calcium carbonate and soda ash.

Approximate composition: Na2O.CaO.6SiO2

Properties:

a) They are low cost.

b) It is resistant to water.

c) It is attacked by common reagents like acids.

Uses:

Window glasses, electric bulbs, bottles, jars, cheaper table wares, where high temperature –

resistance and chemical stability required.

2). Potash lime or Hard glass:

Raw materials: silica, calcium carbonate and Potassium carbonate.

Approximate composition: K2O.CaO.6SiO2

Properties:

a) Possess high melting point so it will not fuse easily.

b) Less acted upon by acids, alkali and other solvents than ordinary glasses.

Uses:

Chemical apparatus, combustion tubes, which are to be used for heating operations.

3). Lead glass or Flint glass:

Raw materials: Lead oxide and silica are fused.

Approximate composition: K2O.PbO.6SiO2

Properties:

a) Lower softening temperature than soda- glass.

b) Higher refractive – index.

c) Has excellent electrical properties.

d) High specific gravity ( 3 to 3.3)

Uses:

High quality table wares, optical purposes(like lenses), neon sign tubing, cathode ray tubes,

electrical insulators and in art objects.

High lead content glasses are used for extra-dense optical glasses for windows and shields to

protect personnel from x-rays and gamma rays in medical and atomic energy fields respectively.

4). Boro silicate glass / Pyrex glass / Jena glass.

Raw materials: silica, boron with a small amount of alumina and some oxides.

Approximate composition: SiO2(80.5%),B2O3(13%), Al2O3(3%),K2O(3%),Na2O(0.5%)

Properties:

a) Low thermal efficient of expansion

b) High chemical resistance.

c) Very high softening points.

d) Excellent shock-proof.

Uses:

Used in industry for pipelines for corrosive liquids, gauge glasses, superior laboratory

apparatus, kitchenware, chemical plants, television tubes, electrical insulators.

5). Aluminosillicate glass

Raw materials: alumina, silica, boron with a small amount of and some oxides.

Approximate composition: SiO2(55%),Al2O3(23%),B2O3(7%), MgO(9%),CaO(5%),

Na2O+K2O(1%)

Properties:High softening temperature

Uses:

High-pressure mercury discharge tubes, chemical combustion tubes, certain domestic

equipments, etc,

6). Glass wool:

It is a fibrous wool-like material, composed of intermingled fine threads of filaments of glass. They

are completely alkali free. The glass filaments are obtained by forcing molten glass through small

offices. The average diameter of the office is 0.0005 to 0.007mm. then the filaments of glass so

obtained are thrown over a rapidly rotating drum to get wool-like materials.

Properties:

a). fire- proof and heat proof material.

b). low electrical and thermal conductivity.

c). resistant to water and most of chemicals.

d). high tensile strength – 8 times that of steel.

Uses:

1. Heat insulation purpose- domestic and industrial appliances.

2. Air filters and dust filtering materials.

3. insulation of metal pipelines and walls and roofs of houses.

4. used in filtration of corrosive liquids like acids.

5. Manufacture of fibre-glass, by blending with plastic resins.

1. How fuels are classified. Give one example for each.

Based on Occurrence - 2 Types.

1. Primary Fuels – It occurs in nature such as. Ex: Coal, Crude oil, Natural Gas.

2. Secondary Fuels – It is derived from primary fuels. Ex: Coke, Petrol, Coal gas.

Based on physical state – 3 types

1. Solid fuels, eg., coal, coke,

2. Liquid fuels eg., gasoline, diesel.

3. Gaseous fuels eg., coal gas, natural gas.

2. Define calorific value. Explain higher & lower calorific value.

It is defined as the amount of heat obtainable by the complete combustion of a unit mass of

the fuel.

Units of Calorific value ; Calorie, kilocalorie, British thermal unit, centigrade heat unit

Higher calorific value / Gross calorific value (GCV)

GCV = The total amount of heat is produced, when a unit quantity of the fuel is completely burnt

and the products of combustion are cooled to room temperature is known as GCV.

Lower calorific value / Net calorific value (NCV)

NCV = The total amount of heat is produced, when a unit quantity of the fuel is completely burnt

and products of combustion are allowed to escape is known as NCV

NCV = GCV -0.09H x 587.

CY6251, ENGG. CHEMISTRY-II / 2 MARKS Q &A

UNIT-V, fuels and combustion

3. Explain proximate analysis. Give its significance.

It involves the determination of % of moisture content, volatile matter, ash content &

fixed carbon in coal.

(i) Moisture content: About 1 gram of air-dried powdered coal sample is taken in a crucible & it is

heated at 100-105°C for 1 hour.

(ii) Volatile matter: After the analysis of moisture content, the crucible with residual coal sample is

converted with lid & it is heated upto 950°C for 7 minutes.

(iii) Ash content: After the analysis of volatile matter the crucible with coal sample is heated without

lidupto 750°C for 30 minutes.

(iv)Fixed carbon: It is determined by the subtracting the sum total of moisture, volatile & ash

content from 100.

Significance or importance of Proximate Analysis:

(i) High % of moisture is undesirable because it reduces the calorific value of a fuel, & increases

the transport cost.

(ii) High % of matter is undesirable because it reduces the calorific value of a fuel & coal burns with

a long flame & high smoke.

(iii) High % of ash content is undesirable because it reduces the calorific value of a fuel & makes

the additional cost of disposal of ash.

(iv) High % of fixed carbon in a coal, is greater its calorific value.

loss in weight of thecoal%of moisture incoal= X100

weight of Air-driedcoal

loss in weight of thecoal% of Volatilemater incoal= X100

weight of moisture-freecoal

Weight of ashformed% of ashcontent incoal= X100

weight of driedcoal

% of fixed carbon in coal = 100 - % of (moisture content + volatile matter + ash content)

4. Explain ultimate analysis. Give its significance.

Itinvolves the determination of % of Carbon, Hydrogen, Nitrogen, Sulphur&Oxygen in coal.

1. Carbon & Hydrogen: A known aount of coal sample is burnt with o2 in a combustion apparatus.

In coal carbon & hydrogen are converted into CO2& H2O & those are absorbed by KOH tubes &

CaCl2 tubes.

C + O2 CO2

12 44

H2 + ½ O2 H2O

2 18

2. Nitrogen: It is carried out by Kjeldahl’s method.A known amount of coal is heated with Con.

H2SO4 in presence of K2 SO4 catalyst in a long necked flask called Kjeldahl’s flask. Nitrogen is

converted into ammonium sulphate. Then it is heated with NaOH& absorbed by HCl.

3. Sulphur: A known amount of coal is completely burnt in a bomb calorimeter. Here sulphur is

converted into sulphate& treated with BaCl2, BaSO4 is obtained.

2BaCl-

2 4 4S+O SO BaSO

32 233

4. Oxygen: The % of oxygen is calculated as follows,

Importance or significance of Ultimate analysis:

1. Higher % of carbon & hydrogen, better is the quality of coal & higher its calorific value.

2. Should have very little nitrogen content.

3. Presence of sulphur is undesirable because it forms harmful gases during the combustion.

4. Lower of the Oxygen increases the higher its calorific value.

Increase weight in KOHtubes 12% of Carbon in coal =   X   X 100

Weight of coal sample taken 44

                                           

2Increase weight inCaCl tubes 2

% of Hydrogen in coal =   X     X 100 Weight of coal sample taken  18

                                                 

volume of acid consumed% of Nitrogen in coal = 1.4 X    X  Normality.

Weight of coal sample

                                                                   

4weight ofBaSO obtained 32

% of Sulphur in coal =    X      X 100Weight of coal sample   233

                                                      

% of Oxygen in Coal = 100 - % of ( C + H+N+S+ash)

5. How Metallurgical coke is manufactured by Otto-Hoffman’s method?

When bituminous coal is heated strongly in the absence of air, the volatile matter escapes

out & the mass becomes hard, strong, porous, which is called metallurgical coke.

Manufacture of Metallurgical coke by “Otto- Hoffman’s by products” method:

In order to (i) Increase the thermal efficiency of the carbonization process &

(ii) Recover the valuable by products by this method.

This oven consists of a number of silica chambers.

Each chamber is about 10-12 m long, 3-4 m height & 0.4 – 0.45m wide.

Coal is introduced into the silica chambers & heated 1200°C by air & producer gas.

I & IV regenerators are heated by hot flue gases & II & III regenerators are heated by

incoming air &producergas.

When the process is complete, the coke is removed & cool by with water.

Time taken for this process is 12-20 hours.

The yield of the coke is about 70%

From out coming flue gas, it gives valuable products like Tar, ammonia, benzene. H2S are

obtained.

Recovery of by products:

(i) Tar: the flue gases are first passed through a tower, in which liq. NH3 is sprayed, tar is

collected at the bottom of the tank.

(ii) Ammonia: The gases are then passed through 2nd tower, in which water is sprayed & NH3

gets in the form of NH4OH.

(iii) Naphthalene: The gases are again passed through next tower, cooled water is sprayed,

Naphthalene gets & condensed.

(iv) Benzene: The gases are passed through next tower, petroleum oil is sprayed, benzene gets

condensed.

(v) H2S gas: The remaining gases are then passed through a purifier, H2S gas is obtained.

The final gas left out is called coal gas.

Advantages:

(i) Valuable by product like NH3, benzene, etc are obtained.

(ii) The carbonization time is less.(iii) Heating is done by extremely by producer gas.

6. What do you mean by hydrogenation of coal? How Synthetic petrol is manufactured by

Bergius Process? Or How solid fuel is converted into liquid fuel? Explain in detail.

The preparation of liquid fuels from solid coal is known as hydrogenation of coal & this

gasoline is known as synthetic petrol.

Bergius Process – Direct method:

Process: Powdered coal is converted into gasoline.

In this process powdered coal is mixed with Ni oleate& heavy oil & made into paste.

It is pumped along with H2 gas into the converter, the paste is heated to 400 - 450°C under

pressure of 200-250atm.

Crude oil comes& it is fractionated into 3 parts.

1. Gasoline. 2. Middle oil. 3. Heavy oil.

The middle oil is further hydrogenated in vapour phase to get gasoline.

The heavy oil is recycled for making paste again coal powder.

60% of yield is obtained from this process.

Input Powdered coal + Ni Oleate catalyst + Heavy oil are made into paste + H2

Heating in 400 - 450°C.

Pressure 200-250atm.

7. Explain the following (i) Compressed natural gas (CNG)

(ii) Liquid petroleum gas. (LPG)

(i) Compressed Natural Gas:(CNG)

Natural gas (CH4) compressed to a pressure of about 1000 atm is known as CNG.

Its calorific value is 12000-14000kcal/m3.

It is fully of methane only & derived from natural gas.

Its composition is as follows.

CH4 = 70-90%

C2 H2 = 5- 10 %

H2 = 3%

Uses: CNG is a cheapest, clearest & the least polluting fuel for automobiles instead of petrol or

diesel.

(ii) Liquid Petroleum Gas: (LPG)

It is obtained as a by- product during the cracking of heavy oil.

Its composition is

Butane = 27%

Isobutene = 25%

Butylenes = 43%

Propane = 5%

Its calorific value is 27,800 kcal /m3.

LPG is marketed under the trade names like Indane, HP, Bharat gas in steel cylinders under

high pressure.

A small amount of Ethyl mercaptan is added during filling of cylinders to help in detecting

leakage of gas.

LPG ensures complete combustion with no smoke & causes the least environmental

pollution.

Uses:

1. It is used as a domestic fuel.

2. It is used as a fuel in vehicles (i.e) motor fuel.

3. It is used in industries & laboratories.

8. Explain Water gas with reaction.

It is a mixture of CO & H2 with small amount of N2.

Its calorific value is about 2800kcal/m3.

Composition:CO = 41%, H2 = 51%, N2 = 4% & CO2 = 4%.

The water gas producer consists of a tall steel vessel, lined with refractory bricks.

It is provided with cup & cone feeder at the top & side opening for water gas exists.

At the bottom it is provided with 2 inlet pipes for passing air & steam.

When steam & little air is passed alternatively over a red hot coke maintained

at about 900-1000°C in a reactor, water gas is produced.

Two steps of reaction in production of water gas:

Step 1: C + H2O CO + H2. ENDOTHERMIC

Coke steam water gas

Here the steam is passed through red hot coke, where CO & H2 gases are produced.

The reaction is endothermic.

Step 2: C + O2 CO2. EXOTHERMIC.

Uses:

1. It is used for preparation of power alcohol.

2. For the production of H2& in synthesis of NH3.

3. To manufacture synthesis petrol in Fischer – Tropsh process.

9. Explain Producer gas with reaction.

It is a mixture of CO & N2 with small amount of H2.

Its calorific value is about 1300 kcal/m3.

Composition: CO = 30%, H2 = 10-15%, N2 = 51-56% & others = rest.

The producer gas producer consists of a tall steel vessel, lined inside with refractory bricks.

It is provided with cup & cone feeder at the top & side opening for producer gas exit.

At the bottom it is provided with an one inlet for passing air & steam.

When a mixture of air & steam is passed over a red hot coke at 1100°C in a reactor,

the producer gas is produced.

C + (O2 +N2) CO + N2.

Coke from air producer gas

Uses:

It is a used as a reducing agent in metallurgical operations.

Used for heating muffle furnaces & open- hearth furnaces.

10. Describe flue gas analysis by Orsat’s apparatus method.

Flue gas analysis is carried out by Orsat apparatus method.

A mixture of gases like CO2, CO, O2& N2etc coming out from the combustion chamber is

called flue gases.

If the flue gas contains,

CO -- It indicates incomplete combustion &

O2 --It indicates excess supply of air used in combustion.

Apparatus: It consists a horizontal tube. At one end this tube, U tube containing fused CaCl2 is

connected through 3 way stop cock. The other end is connected with a graduated burette. The

horizontal tube is also connected with 3 different absorption bulbs I, II, III for absorbing CO2, CO

and O2.

I bulb: It contains KOH solutions & it absorbs CO2 only.

II bulb: It contains Alkalinepyrogallol solution & it absorbs CO2, & O2

III bulb: It contains Ammoniacal cuprous chloride solution & it absorbs CO2,CO& O2

The 3 way stop cock is connected with flue gas supply & it is sucked into the burette & it is

adjusted by 100cc. then the 3 way stop cock is closed. In bulb I, co2 is absorbed by KOH solution

& I is closed & II stopcock is opened, O2 is absorbed by alkaline pyrogallol solution. Now II is

closed & III is opened. CO is absorbed by ammonical cuprous chloride. The decrease in volume

of the flue gas in the burette indicates the volume of I CO2, II O2,

III COrespectively.

Significance: It gives an clear idea about the complete or incomplete process.

11. Explain fractional distillation of crude oil .