Question

Sulphur is used for the vulcanization of rubber to make it:
A.) Hard
B.) Elastic
C.) Malleable
D.) Soft

Answer 1

Hint: Try to recall that natural rubber is thermoplastic and it becomes soft and sticky when heated at high temperature and brittle at low temperature. So, to improve its physical properties natural rubber is vulcanized with sulphur. Now, by using this you can easily find the correct option from the given options.

Complete step by step solution:
It is known to you that natural rubber has no cross-links between the polymer chains.
Some physical properties of natural rubber are as follows:
It becomes soft and sticky at high temperature (>335K) and brittle at low temperature (<335K).
Natural rubber shows high water absorbing capacity and is non-resistant to the attack by oxidizing agents.
Also, it is not hard and tough and has low elasticity and tensile strength.
These properties of natural rubber can be modified and improved by the process of vulcanization.
Vulcanization is the process of heating natural rubber with sulphur to improve its physical properties.
It has been seen that the vulcanized rubber has excellent elasticity, low water absorption tendency, resistant to oxidizing agents and organic solvents.
Therefore, from above points we can say that option B is the correct option for the given question.

Note: It should be remembered to you that the amount of stiffness of vulcanized rubber depends upon the amount of sulphur added. For example: about 5% sulphur is used for making tyre rubber.
Also, you should remember that any vulcanised rubber is capable of getting stretched to about twice of its length and then returns to its original shape and size as soon as the external stretching force is removed.