This set of Engineering Chemistry Multiple Choice Questions & Answers (MCQs) focuses 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
Explanation: 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?
c) Tetra ethyl lead
d) Vanadium penta-oxide
Explanation: 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)?
Explanation: 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
Explanation: 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.
Explanation: 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
Explanation: 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
Explanation: 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
Explanation: 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 %
Explanation: 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
Explanation: 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.
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