JEE Main 2022 · 26 July · evening · Single correct · +4 / −1
Vulcanization of rubber is carried out by heating a mixture of
- (a) isoprene and styrene
- (b) neoprene and sulphur
- (c) isoprene and sulphur
- (d) neoprene and styrene
Answer and solution
Answer (c) isoprene and sulphur
Solution
Chemistry ma’am · 4 steps
Vulcanization is natural rubber plus sulphur, and natural rubber is just polyisoprene.
- What rubber is. Natural rubber is cis-1,4-polyisoprene, a polymer of isoprene (CH₂=C(CH₃)-CH=CH₂). In options like these, "isoprene" stands for this natural rubber.
- Why it needs treating. Raw rubber chains are held together only by weak forces. So it turns soft and sticky when hot, goes brittle when cold, and absorbs a lot of water.
- What sulphur does. Heating raw rubber with sulphur (and an accelerator) at about 373 to 415 K makes sulphur bridges between chains at the reactive sites next to the double bonds. These cross-links make the rubber harder, less sticky and elastic over a wider temperature range.
- So. Vulcanization heats isoprene rubber with sulphur, which is option (c).
The idea to keep. Vulcanization means sulphur cross-links between polyisoprene chains. Whenever you see vulcanized rubber, think natural rubber plus sulphur.
Answer from the NTA final answer key. Solution by PrepWiser.