CY6251 ENGINEERING CHEMISTRY TWO MARK WITH ANSWER

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CY-6251-ENGINEERING CHEMISTRY-II

TWO MARKS

II-SEMESTER

COMMON TO ALL BRANCHES

ANNA UNIVERSITY

REGULATIONS 2013



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UNIT I

WATER TECHNOLOGY

1.Define boiler feed water?

The water, which is fed into the boiler especially for the production of steam, is

called boiler feed water.

2.What are the objectives of boiler feed water?

Prevention of scaling in boiler by using chemicals.

Prevention of corrosion in boiler by using corrosion inhibitors. Prevention of stress corrosion cracking.

Prevention of steam contamination.

3.What are the disadvantages of using Hard water in boilers?

The following are the disadvantages of using hard water in boilers are as follows:

Scale and sludge formation Caustic embrittlement.

Priming and foaming

Corrosion

4.Write short notes about desalination of brackish water?

Water containing high concentrations of dissolved salts is known as brackish

water. Sea water containing about 3.5% of salts is an example of brackish water.

Brackish water is unfit for most of the domestic and industrial applications before

removal of the high concentration of salts. The process used for the removal of



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salts is called desalination. There are different methods employed to remove the

excess salts. Distillation , feezing, electrodialysis and reverse osmosis.

5.Define Reverse osmosis?

A semi permeable membrane permits only solvent molecules to pass through it but

not the solute molecules. When two solutions of different concentrations are

separated by a semipermiable membrane , solvent from dilute side will move

towards concentrated side due to osmotic pressure existing across membrane. This

is known as osmosis. The solvent can be forced to flow in opposite direction that is

from the more concentrated side to the dilute side by applying a hydrostatic

pressure on the more concentrated side . This is the princiople of Reverse osmosis.

6. What are the internal treatment methods?

The internal treatment methods are as follows :

Carbonate conditioning

Colloidal conditioning

Treatment with sodium aluminate

Calgon conditioning

Phosphate conditioning

Radio active conditioning

Electrical conditioning

7.Define priming?

During production of the steam in the boilers , rapidly some droplets of water are

carried along with the steam. The mixing of water sroplets with steam is called wet

steam. This process of wet steam formation is called priming.



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8.Define foaming?

Foaming is the formation of foams in boiler which do not break off easily. Oily

substances which reduce the surface tension of water, contribute to foaming. Both

priming and foaming which generally occur together are disadvantageous in

boilers as the dissolved salts carried by them get deposited on the turbine blades

and other machinery parts thereby decreasing their lives.

9.Define alkalinity?

Alkalinity the another important characteristics of water may be due to the

presence of hydroxide , bicarbonate and carbonate ions.

10.How boiler corrosion occurs?

Boiler corrosion is the decay of boiler material due to chemical or electrochemical

attack of its environment. The corrosion in boilers is due to dissolved CO2 ,

dissolved oxygen and mineral acids produced by the hydrolysis of dissolved salts.

UNIT II

ELECTROCHEMISTRY AND CORROSION

1. What is electrode potential?

The tendency of an electrode to lose or gain electrons, when it is in contact with its

own ions.2. What is an electrochemical cell?

A device used to convert the chemical energy produced in a redox reaction into

electrical energy.



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3. Write the Nernsts equation for the electrode reaction?

Mn+(aq) + ne- M(s)

EMn+/M = E0

Mn+/M + 2.303 RT/ nF log [Mn+(aq)]

4. Define a reference electrode?

The tendency of an electrode to lose electrons, when it is in contact with solution

of its own ions.

5. Why glass electrode cannot be used for solution of pH above 9.0?

At pH above 9.0, the ions of the solution affect the glass interface and

render the electrode useless.

6. Glass electrode is preferred to quinhydrone electrode in measuring pH of a

solution. Give reason.

Glass electrode is simple, not easily oxidized and attains equilibrium rapidly. It can

safely be used up to pH of 10. On the other hand, quinhydrone electrode can be

used upto a pH of 8 only. Moreover, it cannot be used in solutions containing

redox system. Hence, use of glass electrode in pH measurement is preferred over

quinhydrone electrode.

7. What is galvanic cell or voltaic cell?

It is a simple device of producing electrical energy by chemical reaction, e.g.,

Daniel cell. Such a cell is also known as electrochemical cell.

ZnSO4 CuSO4

Zn -------- >Zn+2 + 2e~(oxidation)

Cu2+ + 2e --------- >Cu (reduction)

In the above cell Zn-electrode is anode and Cu-electrode is cathode.



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8. What is an electrolytic cell?

It is a device used for converting electrical energy into chemical energy.

9. What do you meanby electrode potential (E)?

It is the tendency of an electrode in a half cell to lose or gain electrons when it is

in contact with the solution of its own ions.

10. What are reduction and oxidation potentials?

Reduction potential is the tendency of an electrode in a half cell to gain electrons

and oxidation potential is the tendency of an electrode in a half cell to lose

electrons.

11. What do you meanby standard electrode potential (E)?

It is the electrode potential of a metal in contact with its ions when the

concentration of ions is 1 M (1 molar).

12. What is a salt bridge?

It is an inverted U-tube containing an electrolyte (e.g.,KC1, KNO3). It connects

(acts as a bridge) the solutions of the two half cells.

13. What is the E.M.F. of a cell?

It is defined as the potential difference between the two terminals of the cell

when no current is drawn from it.

14.What is an indicating electrode?

It is an electrode in balance with an redox couple, the potential of which

is given by Nernst equation.

15. What are reference electrodes?

These are the electrodes whose potential is constant and

independent of the composition of the contacting solution.

The most widely used are saturated calomel electrodes (G = + 0.246 V) and

the silver-silver chloride electrode (e = + 0.222 V).



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16. Define the electrochemical series?

When the standard reduct ion potent ials of the electrodes are arranged in an

increasing order, the series so obtained is known as electrochemical series.

17. What is corrosion?

The destruction of metals or alloys by the action of gaseous atmosphere,

water or any other reactive liquid medium is known as corrosion.

18.Mention the conditions for wet corrosion to takes place?

When two dissimilar metals are in contact with each other in presence

of aqueous solution or moisture, electrochemical or wet corrosion occurs.

When a metal is exposed to an electrolyte with varying amount of oxygen,

then also wet corrosion takes place.

19.What is Pilling Bedworth ratio? Give its significance?

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

called Pilling Bedworth ratio. It gives an idea about whether the oxide film formed

on the metal surface is protective or non-protective.

20.How do you classify the corrosion?

Chemical corrosion - it involves direct chemical action between metals and

gases.

Electrochemical corrosion - it involves deterioration of metal due to flow

of electric current from one point to another.

Dry corrosion - it refers to the corrosion of metals involving direct chemical

action between metals and dry gases.

Wet corrosion- it involves flow of electric current from one point to another

through some perceptible distance in the presence of liquid or moisture in

air.



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21. What is dry corrosion? Give examples.

Dry corrosion is the direct chemical attack of metals by the gases such as O2, CO2,

SO2, H2O etc.Eg: - i) Tarnishing of silver articles in H2O gas.

ii)Action of dry HCl on iron surfaces.

22.What is wet corrosion?

It is a type of corrosion which occurs when a conducting liquid is in contact with

metal (or) two dissimilar metals or alloys either immersed or partially dipped in

a solution.

23. What is galvanic corrosion?

When two metals are electrically connected and exposed to an electrolyte, the

metal higher in electrochemical series undergoes corrosion. Eg; Zn-Cu couple, Zn

gets corroded.

24. What is pitting corrosion?

Pitting is a localized attack which results in the formation of a hole around which

the metal is relatively unattached. The mechanism involves setting up of

differential aeration cell.

25.Name the factors which affect corrosion.

Air and Moisture

Electrolyte in water

pH of the medium

Presence of corrosive gases

Presence of impurities in a metal



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26.A steel screw in a brass marine hardware corrodes.?Give reason.

This is due to galvanic corrosion. Iron which is higher in the emf series becomes

anodic and is corroded. Brass which is present lower in series acts as cathodic and

is not corroded.

27. Iron corrodes under drops of salt water.?Explain.

This is due to differential aeration. Areas of iron covered by drops, having poor

access to oxygen, become anodic with respect to other areas which are freely

exposed to air. Due to electrochemical corrosion, the areas under drops undergo

corrosion, while the freely exposed parts remain unaffected.

28. The rate of metallic corrosion increases with increase in temperature. Give

reason.

With increase of temperature of the environment, the rate of reaction as well as

rate of diffusion increases, thereby corrosion rate increases.

29. Iron corrodes faster than aluminium, even though iron is placed below

aluminium in emf series. Why?

This is because aluminium forms a non-porous, very thin, tightly adhering

protective oxide film (Al2O3) on its surface and this film does not permit corrosion

to occur.

30. Rusting of iron is quicker in saline water than in ordinary water. Give

reason.

The presence of sodium chloride in saline water leads to increased conductivity of

water layer in contact with the iron surface, thereby corrosion current increases and

rusting is speeded up.



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31. What is cathodic protection? Mention its two applications.

Cathodic protection is the reduction or prevention of corrosion by making

metallic structure as cathode in the electrolytic cell. This can be done by either

using sacrificial anodic (or) impressed current cathodic method. They give

protection to cables, pipelines, ship hulls from marine corrosion.

32. What is impressed current cathodic protection?

It is a method in which an impressed current (greater than corrosion current) is

applied in opposite direction to nullify the corrosion, thereby converting the

corroding metal from anode to cathode.

33. What are corrosion inhibitors? Give examples.

Corrosion inhibitors are substances which are added to the corrosive

environment to decrease the corrosion rate.

Eg. Anodic inhibitorsphosphates & chromates.

Cathodic inhibitorsaniline and its derivatives.

34.What is the role of pigment in paint? Give examples.

Pigments are solid substances and they provide color to the paint.

They provide capacity to the paint.

They give protection to the paint film by reflecting harmful UV radiation.

Eg. Greenchromium oxide

BluePrussian blue.

35.What is meant by electroplating?

Electroplating is the process by 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 coat metal.



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UNIT III

ENERGY SOURCES

1.Define nuclear fission. Give example?

Nuclear fission is defined as the process of splitting of heavier nucleus into two or

more smaller nuclei with simultaneous liberation of large amount of energy.

2.Mention any few important characteristics of nuclear fission?

A heavy nucleus (U235

or Pu239

) , when bombarded by slow moving

neutrons , split into two or more nuclei. Two or more neutrons are produced by fission of each nucleus.

Large quantities of energy is produced as a result of conversion of small

mass of nucleus into energy.

3.What is nuclear fusion?

The process of combination of lighter nuclei into heavier nuclei, with simultaneous

liberation of large amount of energy. Nuclear fusion occurs in sun.

4.What is nuclear chain reaction?

A fission reaction , where the neutrons rom the previous step continue to propagate

and repeat the reaction is called nuclear chain reaction.



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5.Differnce between nuclear fission and nuclear fusion?

S.NO NUCLEAR FISSION NUCLEAR FUSION

1 It is the process of breaking a heavier It is the process of combination of

nucleus lighter nuclei

2 It emits radioactive rays It does not emit any kind of rays.

3 It occurs at ordinary temperature. It occurs at hugh temperature.

6.What is Super critical mass?

If the mass of the fissionable material (U235

) is more than the critical mass, it is

called super critical mass.

7.What are the types of nuclear fission reaction?

The nuclear fission reactions are of two types 1) uncontrolled fission reactions 2)

controlled fission reactions.

8.What is a nuclear reactor?

The arrangement or equipment used to carry out fission reaction under controlled

conditions is called a nuclear reactor.

9.What is a light water nuclear power plant?

Light water nuclear power plant is the one, in which U235 fuel rods are submerged

in water . Here the water acts as coolant and moderator.

10.What are moderators?

The substance used to slow down the neutrons are called moderators.



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11.What are the general components of a nuclear reactor?

Fuel rods

Control rods

Coolents

Moderators

Pressure vessel

12.What is Breeder Reactor?

Breeder reactor is the one which converts non-fissionable material into fissionable

material.

13.What is solar cell or Photogalvanic cell?

Photogalvanic cell is the one, which converts the solar energy directly into

electrical energy.

It consists of a p-type semiconductor and n-type semiconductor. They are in

close contact with each other.

As the solar energy is available freely and also it is pollution free, in future

its utility is very important.

14.What are the applications of solar cells?

Solar cells are used in calculators, electronic watches, radios and TVs.

Solar cells are superior to other type of cells, because these are non

polluting and eco-friendly.

Solar energy can be stored in Ni-Cd batteries and Lead-Acid batteries.

Solar cells can be used to drive vehicles.



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Solar cells, made of silicon are used as a source of electricity in space craft and

satellites.

15.What are fuel cells?

Fuel cell is a voltaic cell, which converts the chemical energy of the fuels directly

into electricity without combustion. It converts the energy of the fuel directly into

electricity . In these cells, the reactants, products and electrolytes pass through the

cell.

16.What is a battery? How does it differ from a cell?

A battery is an arrangement of several electrochemical cells, connected in series,

that can be used as a source of direct electric current,

A cellContains only one anode and cathode.

A BatteryContains several anodes and cathodes.

17.What is a primary battery? Give eg?

Primary cells are cells in which the electrode and the electrode rections cannot be

reversed by passing an external electrical energy. The reactions occur only once

and after use they become dead. Therefore , They are not chargeable.

Eg : Leclanches cell.

18.What are secondary cells?

Secondary cells are cells in which the electrode reactions can be reversed by

passing an external electrical energy. Therfore they can be recharged by passing

electric current and used again and again . These are also called storage cells or

Accumulators.

19.Describe lithium battery?



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The lithium battery consists of a lithium anode and a TiS2cathode . A solid

electrolyte , generally a polymer, is packed in between the electrodes. The

electrolyte permits the passage of ions but not that of electrons.

20.What are the advantages of Li-S battery?

Li-S battery has light weight unlike the lead acid battery.

It possess a high energy density.

It is used in electric cars.

UNIT IV

ENGINEERING MATERIALS

1.Define Abrasive?

Abrasives are hard substances used for polishing, shaping, grinding, operations.

They are characterized by high melting point, high hardness and chemically

inactive.

Natural abrasive- Diamond, Quartz, Corundum, Emery

Artificial abrasives- Silicon carbide, Boron carbide

2. What are soft abrasives?

Abrasives having their hardness 1-4 Mohs scale are known as soft abrasives.

3.What is abrasive power?

It is the strength of an abrasive to grind away another materials. It depends onhardness, toughnesss and refractoriness.



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4.What is hardness of an abrasive?

It is the ability of an abrasive to grind or scratch away other materials. The harderthe abrasive quicker will be its abrading action.

5.Mention some important applications of abrasives?

To clean the surface orior to coating abrasive powders are used. Eg- Quartz,garnet.

To prepare smooth wood, metal and plastic surfaces, abrasive paper is used.Eg- Alumina, Silicon carbide.

To remove the scales from iron surfaces, grinding wheels are used.

6.Mention some important characteristics of abrasives?

It should be very hard.

It should resist the abrading action.

It should be chemically inactive.

It should posses high refractoriness.

It should have high melting point.

7.What is diamond? Mention its types?

It is a pure crystalline carbon. It is the hardest known substance. Its hardness in 10on Mohsscale. It is chemically inert and not affected by acids or alkalis. The off-

colour diamond is called borts and black colour diamond is called carbonado.

8.What are Natural abrasives?

Natural abrasives are abrasives available and obtained in the nature as such.

9.What are Synthetic abrasives?

Synthetic abrasives are the man made abrasives obtained by some chemicalreactions.

10.How are abrasives used?

Abrasives are used in three forms:

As loose powder



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As abrasive paper or cloth

As grinding wheels.

11.Define refractories?

Refractories are materials which can withstand very high temperature without

undergoing softening , melting or deformation. These materials can withstand heat

excellently and hence they can be used as lining in industrial furnaces which are

operated at high temperature.

12.What are the characteristics of a good refractory?

A good refractory should posses following characteristics:

It should be able to withstand the temperature to which it is exposed.

It should be chemically inert under the service conditions in which it is

employed.

It should not react with reactants or products in the furnace.

It should possess good thermal strength.

It should have excellent resistance to change in volume at high temperature.

13.Mention the classification of refractories?

Refractories are classifies into three types based on the condition used. They are

Acid refractories

Basic refractories

Neutral refractories

14.Define thermal spalling?

Spalling means cracking , fracturing or peeling off in the refractory lining of the

furnace.



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15.What are the causes for spalling?

On sudden heating or cooling of the furnace , uneven expansion or contraction may

occur and this leads to appalling. A refractory with low efficient of expansion and

high thermal diffusivity have high spalling resistance. A good refractory materials

should have good resistance to thermal spalling.

16. How can we prevent spalling?

The spalling can be minimized by avoiding sudden change of furnace temperature,

using high porosity , low coefficient of expansion and good thermal conducting

refractory materials and by modifying the furnace design.

17.Define RUL?

Refractoriness under load. Refractoriness used in metallurgical operations and

industries have to withstand varying loads, tension and stress without deformation

at high temperature. Hence refractories should have high mechanical strength

under operating conditions.

18.Define Dimensional stability?

It is the resistance to any volume changes of a refractory material when subjectedto high temperature. Eg are as follows

The contraction of magnesite bricks during service life

Expansion of silica bricks during service life.

19.Define porosity?

The porosity of the refractory material is the ratio of its pore volume to the bulkvolume. Properties like strength, thermal spalling, thermal conductivity are

influenced by its porosity .



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20.Define thermal Expansion?

The expansion of a refractory with changing temperature should be negligible. Itthis effect were appreciable the furnace lining would undergo cracking.

UNIT V

FUELS AND COMBUSTION

1. Define a fuel.

Fuel is a combustible substance, which on combustion produces a large amount of

heat, which can be used for various domestic and industrial purposes. The fuels

commonly used contain carbon as the main constituent and some common fuels

are wood, charcoal, kerosene, diesel, producer gas etc.

2. What is meant by Gross Calorific Value?

The quantity of heat evolved by the combustion of unit quantity of fuel is its gross

calorific value (GCV). Gross or higher calorific value is the quantity of heatliberated by combusting unit mass of fuel in oxygen, the original material and the

final product of combustion being at a reference temperature of 25C and the water

obtained in the liquid state, represented by GCV or HCV.

3. Define Net Calorific Value?

Net calorific value (NCV) is the quantity of heat evolved when a unit quantity of

fuel is burnt in oxygen, the original material and the final products of combustion

being at a reference temperature of 25C and the water obtained from the fuel

being at the vapor state. The net calorific value is hence always less than the gross

calorific value by the amount corresponding to the heat of condensation of water



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vapours i.e., 587.0 kcal/kg NCV = HCV Latent heat of water vap. Formed =

HCV - Mass of hydrogen x ax Latent heat of steam

Since 1 part by mass of hydrogen produces 'a' part by mass of water.

4.What is a coke?

It is a carbonaceous residue obtained from the destructive distillation of coal,

petroleum and coal tar pitch. Petroleum yields coke during cracking processes. The

main source of coke is coal. Petroleum coke is used as metallurgical coke since it

is pure.

5. What is an anti-knocking agent?

They are organometallic compounds that increase the octane number of gasoline

when added in low percentage to it. Most common is TEL (-tetraethyl lead). They

can increase the octane number over 100%.

6.What are the requirements of a good fuel?

It should be cheap and readily available.

It should have higher calorific value.

It should have moderate ignition temperature.

The combustion should be easily controllable.

It should have low ash content and low non combustible matters.

It should be safe and economical for storage and transport.

It should not undergo spontaneous combustion.

7.how are fuels classified?

Fuels are classified into 1) Primary fuelseg Coal , petroleum, natural gas.

2) Secondary fuelseg Coke, gasoline, coal gas.



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Both primary and secondary fuels may be further sub- classified into three types

based on their physical state as 1) Solid fuels

2)Liquid fuels

3)Gaseous fuels.

8.What are primary and secondary fuels?

Primary fuels occur in nature while secondary fuels are derived from primary fuels.

9.List the advantages of liquid fuels?

Liquid fuels have higher calorific value than solid fuels.

They occupy less storage space than solid fuels

Their combustion is uniform and can be controlled.

They do not yield any ash after burning.

10.List the advantaged of Solid fuels?

Solid fuels are easily available and are very cheap.

Handling and transportation are easy.

They have moderate ignition temperature.

They can be stored economically without any risk.

11.Mention the disadvantages of Solid Fuels?

They form large amount of ash while burniong .

The disposal of ash is a big problem.

A large space is required for storage.

Combustion of solid fuel is a slow process and it cannot be easily controlled.



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It requires a lot of air for complete combustion. Hence, its thermal efficiency

is low.

The calorific value is comparatively low.

12.How are gaseous fuels superior to other types of fuels?

Gaseous fuels have high calorific value.

They do not produce any ash or smoke during burning.

Complete combustion is possible.

They have high thermal efficiency.

They can be easily transported through pipes.

13.What is CNG?

CNG is compressed natural gas used in motor engines now-a-days instead of

gasoline fuel causing less pollution.

14. Why is calorific value of coal gas higher than that of producer gas?

Coal gas contains all the combustible gases like CH4, C2H4, C2H2, CO and H2,

whereas producer gas contains CO, H2 and N2. N2 acts as inert diluent. So

calorific value of coal gas is higher than that of producer gas.

15. Producer gas is madeby passing air and steam through a thick bed of coal.

Why?

The primary purpose of steam is to use up the heat developed during exothermic

reaction of coal and O2 of air to maintain the temperature of producer.

16. Why is NCV greater than GCV?

Gross calorific value GCV includes the latent heat steam during combustion of a

fuel, but Net calorific value NCV excludes the latent heat of steam.



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17. What is meant by the term fixed carbon?

It is the pure carbon present in coal. Higher the fixed carbon content of the coal,

higher will be its calorific value.

18.Name the different varities of coal.

Peat

Lignite

Sub-bituminous

Bituminous Anthracite

19.Define cetane number?

Cetane number is defined as the percentage of cetane in cetane-2-methyl

naphthalene mixture which has the same ignition delay as the diesel iol when burnt

in a standard test engine under standard conditions.

20.Define octane number?

Octane number is defined as the percentage of iso-octane in iso- octane-n-heptane

mixture which has the same knocking as the gasoline sample when burnt in a

standard test engine under standard conditions.

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CY6251 ENGINEERING CHEMISTRY TWO MARK WITH ANSWER