Category: Engineering Chemistry Objective Questions

Engineering Chemistry Multiple Choice Questions on “Silicones and Polymeric Composites”.

1. Silicones are called inorganic polymers due to absence of _________________in the main backbone chain.
a) Nitrogen atom
b) Oxygen atom
c) Carbon atom
d) Hydrogen atom
Answer: c
Clarification: Silicones are called inorganic polymers due to the absence of carbon atoms in the main backbone chain. Carbon compounds are the basis of organic chemistry.

2. Silicones resemble inorganic polymers in having high % of ____________
a) Ionic character of Si-O bond
b) Organic groups on silicon atoms
c) Controlled hydrolysis
d) Solubility
Answer: a
Clarification: Silicones resemble inorganic polymers in having high % of ionic character of Si-O bond. The bond between silicon and oxygen molecule is very ionic in nature.

3. The catalyst used in the preparation of poly-siloxanes is ____________
a) Benzoyl peroxide
b) Grignard reagent
c) Cumene hydroperoxide
d) Lewis acid
Answer: b
Clarification: The catalyst used in the preparation of poly-siloxanes is Grignard reagent. The Grignard reaction is an organometallic chemical reaction in which alkyl, vinyl, or aryl-magnesium halides, CH₃MgI (Grignard reagents) add to a carbonyl group in an aldehyde or ketone.

4. Which of the following is tri-functional?
a) Dimethyl silicon chloride
b) Trimethyl silicon chloride
c) Tetramethyl silicon chloride
d) Momethyl silicon chloride
Answer: d
Clarification: Momethyl silicon chloride is tri-functional and gives cross-linking to the final polymer.

5. Which of the following gives linear chain silicones on polymerisation by controlled hydrolysis?
a) Dimethyl silicon chloride
b) Trimethyl silicon chloride
c) Tetramethyl silicon chloride
d) Momethyl silicon chloride
Answer: a
Clarification: Dimethyl silicon chloride gives linear chain silicones on polymerisation by controlled hydrolysis. All the other options does not give such type of reaction.

6. Which of the following is mono-functional?
a) Dimethyl silicon chloride
b) Trimethyl silicon chloride
c) Tetramethyl silicon chloride
d) Momethyl silicon chloride
Answer: b
Clarification: Trimethyl silicon chloride is mono-functional and hence, a chain-stopper.

7. The proportion of momethyl silicon chloride determines the amount of cross-linking that can be obtained in polymerisation.
a) True
b) False
Answer: a
Clarification: The proportion of momethyl silicon chloride used in polymerisation determines the amount of cross-linking that can be obtained. It is made on an industrial scale as the principal precursor to dimethyl silicone and polysilane compounds.

8. On increasing the temperature, the viscosity of polysiloxanes ____________
a) Increases
b) Decreases
c) Remain constant
d) First increases then decrease
Answer: c
Clarification: The viscosity of polysiloxanes does not change appreciably with a change in temperature.

9. The bond energy of Si-O bond is ____________
a) 37 kJ/mol
b) 115 kJ/mol
c) 248 kJ/mol
d) 502 kJ/mol
Answer: d
Clarification: The bond energy of Si-O bond is 502kJ/mol. The bond energy is a measure of the amount of energy needed to break apart one mole of covalently bonded gases and Si-O bond is very strong.

10. Silicones have good electrical insulation because they are less stable to heat than organic polymers.
a) True
b) False
Answer: b
Clarification: Silicones have good electrical insulation because they are more stable to heat than organic polymers.

Engineering Chemistry Multiple Choice Questions on “Characteristics of Coal”.

1. How does the texture of coal changes with its maturity?
a) Becomes hard, less brittle and moderately tough
b) Becomes hard, more brittle and more tough
c) Becomes hard, more brittle and less tough
d) No change
Answer: b
Clarification: The texture of coal tends to the layer present on the coal and its maturity is from lignite to anthracite. The number of layers from lignite to anthracite increases due to which the compactness increase, thus increasing its toughness, hardness and brittleness.

2. On what factors does the specific gravity of coal depends?
a) Its calorific value and ash content
b) Its ignition temperature and calorific value
c) Type of coal and ash content
d) Type of coal and calorific value
Answer: c
Clarification: Specific gravity is the ratio of the density/mass of a substance to the density/mass of reference substance. The total ash content represents its mass and
The type of coal is required for its density.

3. Which of the coal have the best heating values in terms of volatile matter?
a) Containing 20% volatile matter
b) Containing 60% volatile matter
c) Containing 30% volatile matter
d) Containing 50% volatile matter
Answer: a
Clarification: Coals containing high volatile matter produces long and smoky flame due to which its heating value decreases. Semi-bituminous coal has the highest heating value due to less volatiles content.

4. Which type of coals have the highest grindability index?
a) Steam coals
b) Gas coals
c) House coals
d) Pulverised coals
Answer: d
Clarification: Grindability is the ease with which a coal can be grounded. The grindability index of pulverised coal is about 100. This is because of the volatile matter present in the coal, the higher the volatile matter of coal, the more will be its grindability index.

5. How does the friability of the coal is tested?
a) Drop shatter test
b) Thermal cracking
c) Knocking
d) Proximate analysis
Answer: a
Clarification: Friability is the tendency of the coal to break into pieces. The more the friability, the less will be the quality of coal. Splint and cannel coal are less friable. Knocking is the unusual sound produced by an engine.

6. Which property of coal is tested in Audibert Arnu test?
a) Bulk density
b) Colour
c) Caking and coking
d) Texture
Answer: c
Clarification: This method uses a dilatometer to find out the swelling properties of coal. Caking is the ability to form a coherent cake when the coal is carbonised. If there is residue formed during carbonisation, then the coals formed are called coking coals.

7. On which property of coal does the design of bunkers for the storage of coal depends?
a) Specific gravity
b) Bulk density
c) Grindability
d) Friability
Answer: b
Clarification: Bunkers/coal bins are the containers in which the coal can be transported. Bulk density is weight of soil present in coal. According to the bulk density the design of containers are generated.

8. Which type of coals are non-caking in nature?
a) Steam coals
b) Gas coals
c) House coals
d) Pulverised coals
Answer: a
Clarification: Steam coals are volatile lignitous coals which are used in steam raising. These coals produce long smoky flames. Gas coals are strongly caking in nature.

9. Phosphorous and sulphur content in the coal tend to make a metal brittle.
a) True
b) False
Answer: a
Clarification: A coal should not contain high phosphorous and sulphur content because coal have a role in number of metallurgical operation due to which it affects the properties of metal and makes it brittle.

10. Which of the following is not a characteristic of coal?
a) Weathering
b) Slaking index
c) Moisture content
d) Bulk density
Answer: c
Clarification: Moisture content represents the total vapours present inside the coal. Moisture develops from the outside atmospheric conditions due to which it is not a characteristic of coal.

Engineering Chemistry Multiple Choice Questions on “Anti Knocking Agents – 1”.

1. How can we increase the octane rating of gasoline?
a) By addition of fuel of low anti-knock value
b) By addition of fuel of high anti-knock value
c) By adding a product of high cetane rating
d) By heating of the fuel
Answer: b
Clarification: Compounds such as casing-head gasoline, cracked and reformed gasoline, benzol and alcohol are added to increase the octane rating of the fuel. The more will be the octane rating, the less will be the knocking in the engine.

2. Which compound is usually added to decrease the knocking in the engine?
a) Sulphur
b) Phosphorous
c) Tetra ethyl lead
d) Vanadium penta-oxide
Answer: c
Clarification: The anti-knocking properties of gasoline are usually increased by adding tetra ethyl lead and the process is called as doping. The molecular formula of tetra ethyl lead is Pb(C₂H₅)₄ .

3. What is the specific gravity of tetra ethyl lead (TEL)?
a) 1.09
b) 1
c) 1.97
d) 1.62
Answer: d
Clarification: Tetra ethyl lead is a colourless liquid with sweet odour. Specific gravity is the ratio of the mass of a substance to the mass of a reference substance for the same given value. 1.09 is the specific gravity of water.

4. How much ml of tetra ethyl lead (TEL) is added to aviation petrol?
a) 1 ml/litre
b) 0.5 ml/litre
c) 2 ml/ litre
d) 3 ml/litre
Answer: a
Clarification: About 0.5 ml of TEL per litre is added for motor spirits and about 1ml of TEL per litre is generally added for aviation petrol. Tetra ethyl lead is highly poisonous in nature.

5. Gasoline containing TEL is colourless to indicate its poisonous nature.
a) True
b) False
Answer: b
Clarification: Some colour is added to gasoline to differ from the gasoline, which does not contain TEL, since TEL is poisonous in nature and has to be use safely. TEL should be added safely to gasoline as it can enter the body through cut or bruise.

6. At what temperature does TEL (tetra ethyl lead) starts getting decomposed?
a) 500 ⁰C
b) 100 ⁰C
c) 900 ⁰C
d) 200 ⁰C
Answer: d
Clarification: TEL (tetra ethyl lead) starts to boil at 200 ⁰C and also starts getting decomposed. At this time it is added to gasoline, so that it can mix uniformly.

7. At most how much ml of TEL can be added, so as to increase the octane rating of aviation fuel?
a) 15 ml per gallon
b) 9 ml per gallon
c) 7 ml per gallon
d) 5 ml per gallon
Answer: c
Clarification: Generally no applicable increase in octane number can be obtained by using more than 7 ml of TEL per gallon. Hence, not more than 7 ml of TEL per gallon are added for aviation fuel.

8. How is knocking produced in a petrol engine?
a) Due to the size of the engine
b) Due to spontaneous combustion in the engine
c) Due to the presence of less impurities in the fuel
d) Due to the parts of the engine
Answer: b
Clarification: Knocking in petrol engine is due to the spontaneous ignition of the last positions of the compressed mixture of petrol and air. This process of ignition of the mixture relatively slows the induction period.

9. What is the work of TEL in addition in petrol engine?
a) It increases its induction period by 200-300 %
b) It decreases the induction period by 50 %
c) It increases the induction period by 50-100 %
d) It increases the induction period by 400-500 %
Answer: a
Clarification: The addition of TEL increases the induction period of the petrol engine by 200-300 % by interaction with the free radicals whereby lead oxide is produced. As soon as the explosive combustion occurs, the lead oxide is rapidly reduced to metallic lead.

10. Which of the following compound is added to the petrol engine to overcome the problems caused by tetra ethyl lead (TEL)?
a) Methylene dibromide
b) Ethylene dibromide
c) Propylene dibromide
d) Butylene dibromide
Answer: b
Clarification: Lead is formed as the final product after adding TEL in the petrol engine which is kind of hazardous in nature. To overcome this problem ethylene dibromide is added to the petrol engine so that the product obtained is lead bromide, which is swept out with the exhaust gases.