This set of Engineering Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Elastomers – 1”.
1. Which of the following is not the essential structural requirement of an elastomer?
a) Long flexible chains
b) Weak intermolecular forces
c) Rigidity in structure
d) Occasional cross-linking
View Answer
Explanation: Elastomers are a long flexible chain; they are not rigid in nature.
2. Natural rubber is ____________
a) Poly isoprene
b) Ethylene glycol
c) Butadiene
d) Acrylonitrile
View Answer
Explanation: Natural rubber is poly (cis) isoprene. Malaysia is one of the leading producers of rubber.
3. The structural formula of isoprene is ____________
a) 2-benzyl-1,3-butadiene
b) 2-methyl-1,3-butadiene
c) 3-benzyl-1,2-butadiene
d) 3-methyl-1,2-butadiene
View Answer
Explanation: The structural formula of isoprene is 2-methyl-1,3-butadiene. It is a common organic compound with the formula CH2=C(CH3)-CH=CH2. In its pure form, it is a colorless volatile liquid. Isoprene is produced by many plants.
4. Select the incorrect statement from the following option.
a) Raw rubber is weak and have low tensile strength
b) Raw rubber is attacked by oxidizing agent
c) In organic solvents, it undergoes swelling and disintegration
d) Raw rubber is durable
View Answer
Explanation: Raw rubber is not durable due to its oxidation in air. All the other options are correct.
5. The temperature at which raw rubber is heated for the vulcanisation process is ____________
a) 0-10 0C
b) 10-50 0C
c) 50-100 0C
d) 100-140 0C
View Answer
Explanation: The temperature at which raw rubber is heated for the vulcanisation process is 100-140 0C. A typical vulcanization temperature for a passenger tire is 10 minutes at 177 °C.
6. In the vulcanisation process, the raw rubber is heated with ____________
a) Oxygen
b) Sulphur
c) Carbon
d) Calcium
View Answer
Explanation: In the vulcanisation process, the raw rubber is heated with sulphur. It is a chemical process for converting natural rubber or related polymers into more durable materials via the addition of sulphur or other equivalent curatives or accelerators. These additives modify the polymer by forming cross-links (bridges) between individual polymer chains.
7. The amount of sulphur added determines the extent of stiffness of vulcanised rubber.
a) True
b) False
View Answer
Explanation: The amount of sulphur added determines the extent of the stiffness of vulcanised rubber. This sulphur modify the polymer by forming cross-links (bridges) between individual polymer chains.
8. Select the incorrect statement from the following option.
a) Vulcanised rubber has excellent resilience
b) Vulcanised rubber has only slight tackiness
c) Vulcanised rubber has high elasticity
d) Vulcanised rubber has tensile strength 10 times more than raw rubber
View Answer
Explanation: Vulcanised rubber has low elasticity and decreases with the extent of vulcanisation. All the other options are correct.
9. The tensile strength(kg/cm 2) of vulcanised rubber is ____________
a) 200
b) 2000
c) 500
d) 5000
View Answer
Explanation: The tensile strength of vulcanised rubber is 2000 kg/cm 2. Cross-linking introduced by vulcanization prevents the polymer chains from moving independently.
10. The percentage of butadiene and styrene in Buna-S is ____________
a) 50% each
b) 60% and 40% respectively
c) 80% and 20% respectively
d) 75% and 25% respectively
View Answer
Explanation: The percentage of butadiene and styrene in Buna-S is 75% and 25% respectively. These materials have good abrasion resistance and good aging stability when protected by additives.
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