Problem 39 - A Complete Resource Book in Chemistry for JEE Main

Question

Ebonite is (a) natural rubber (b) synthetic rubber (c) highly vulcanized rubber (d) polypropene

Step-by-Step Solution

Answer

Ebonite is (c) highly vulcanized rubber.

Step 1: Understand the Composition of Ebonite

Ebonite is also known commonly as hard rubber. It is obtained by vulcanizing rubber with a high percentage of sulfur.

Step 2: Analyze the Vulcanization Process

Vulcanization is a chemical process that involves the addition of sulfur to rubber to improve its durability, elasticity, and hardness. Ebonite contains approximately 30-40% sulfur, making it significantly more vulcanized than other forms of rubber.

Step 3: Evaluate the Options

Consider the options: (a) Natural rubber - This is the raw form of rubber extracted from rubber trees. (b) Synthetic rubber - These are rubber types that are artificially made, like polybutadiene. (c) Highly vulcanized rubber - Matches the description of ebonite which has a high sulfur content. (d) Polypropene - This is a type of thermoplastic polymer, not related to ebonite.

Step 4: Identify the Correct Answer

From the analysis, option (c) "highly vulcanized rubber" closely matches the description of ebonite, as it specifically undergoes intensive vulcanization with sulfur.

Key Concepts

Vulcanization

Vulcanization is a remarkable chemical process that significantly improves the qualities of natural or synthetic rubber. The essence of vulcanization lies in the addition of sulfur. When sulfur is introduced to rubber under high heat, it creates cross-links between the rubber molecules. These cross-links are like bridges that bind the molecules tightly together.

This transformation imparts several enhanced properties to the rubber:

• Durability: The rubber becomes more resistant to wear and tear.
• Elasticity: It gains the ability to stretch and return to its original shape repeatedly.
• Hardness: The rubber becomes tougher and can withstand greater pressure.

This process is what allows rubber to be molded into useful products like tires, which need to endure friction and varied environmental conditions.

Highly vulcanized rubber

Highly vulcanized rubber, like ebonite, stands out due to its significant sulfur content, typically ranging between 30-40%. This high degree of vulcanization results in a rubber form that is extremely hard and rigid. Unlike regular rubber, which remains fairly soft and elastic, ebonite is akin to a durable plastic.

The high sulfur content in ebonite increases the number of cross-links between the polymer chains, which weighs heavily on its distinctive properties:

• Rigidity: It becomes sturdy and firm, making it suitable for products requiring hardness.
• Non-conductive: Ebonite does not conduct electricity, lending itself well to use in insulating products.
• Scratch Resistance: The surface becomes tougher, which is why ebonite often finds use in items like bowling balls and certain musical instruments.

Chemical process in rubber production

The chemical process in rubber production centers around polymer chemistry. Rubber, by nature, is a long chain of polymer molecules that are free to move past each other. This freedom makes natural rubber sticky and not very useful for strong products without additional processing.

Vulcanization changes that. The chemical interaction involves heating the rubber with sulfur, which prompts a reaction that integrates sulfur links in the polymer chains. These links stabilize the molecular structure, preventing the chains from sliding individually. The result is a more cohesive and reliable rubber with enhanced mechanical properties.

This systematic chemical process improves natural and synthetic rubber extensively, extending its utility across various industries. From automotive to household items, this process makes rubber more versatile and adaptable to fulfill multiple demands of everyday products.