In the industrial vulcanization of rubber, which chemical element is commonly added to improve the strength, elasticity and durability of natural rubber?

Introduction / Context:
Natural rubber in its raw form is soft, sticky, and becomes brittle at low temperatures and too soft at high temperatures. To make rubber more useful for tyres, hoses, and many other products, it is chemically treated in a process called vulcanization. This process involves adding a specific element that forms cross links between rubber chains, improving strength and elasticity. The question asks you to identify which chemical element is used for vulcanizing rubber.

Given Data / Assumptions:

• We are dealing with the vulcanization process, an important treatment for natural rubber.
• The options given are sulphur, chlorine, bromine, and phosphorus.
• We assume standard industrial practice for making tyres and other rubber goods.
• The element in question should form cross links between polymer chains.

Concept / Approach:
Vulcanization is the process of heating natural rubber with sulphur, sometimes in the presence of accelerators. Sulphur atoms form cross links between the long polyisoprene chains of natural rubber. These cross links restrict the movement of the chains, making the material stronger, more elastic, and less sticky. Chlorine and bromine are halogens used in certain chemical reactions and polymers, but they are not the primary cross linking agents in classical vulcanization. Phosphorus is used in many industrial processes but not as the main element for vulcanizing rubber. Therefore, sulphur is the correct answer.

Step-by-Step Solution:
Step 1: Recall that natural rubber consists of long chains of polyisoprene that can slide past one another easily, making the material weak and sticky. Step 2: Understand that the purpose of vulcanization is to create cross links between these chains to improve mechanical properties. Step 3: Remember that sulphur is the traditional element added during vulcanization to form these cross links between rubber chains. Step 4: Examine the other elements: chlorine and bromine are halogens mainly associated with disinfection or halogenated polymers, and phosphorus is used in matches and fertilizers, not primarily in rubber cross linking. Step 5: Conclude that sulphur is the element used for vulcanizing rubber and select sulphur as the answer.

Verification / Alternative check:
Chemistry and materials science references describe the discovery by Charles Goodyear that heating natural rubber with sulphur and appropriate additives greatly enhanced its properties. Modern rubber technology still relies on sulphur based vulcanization systems, although formulations may include accelerators and activators. The term vulcanization itself is strongly associated with sulphur cross linking. None of the other elements listed in the options is mentioned as the primary vulcanizing agent in standard texts, confirming that sulphur is the correct choice.

Why Other Options Are Wrong:
Chlorine is used in water disinfection and in the manufacture of PVC and other chlorinated compounds, but it is not the main element used for vulcanization of natural rubber. Bromine is a halogen used in flame retardants and certain organic reactions, again not primarily in rubber cross linking. Phosphorus is important in matches, phosphoric acid production, and fertilizers, but not as the key cross linking agent in vulcanization. These elements do not match the classical definition and practice of vulcanization and therefore cannot be the correct answers.

Common Pitfalls:
Students may be tempted to choose a halogen like chlorine or bromine because of their reactivity, but reactivity alone is not enough; the element must specifically form stable cross links that improve rubber properties. Another pitfall is to mix up uses of chemical elements across industries without focusing on what is described in rubber technology. To avoid such confusion, remember the strong association between sulphur and vulcanization, especially in the context of tyres and automotive rubber parts.

Final Answer:
The element commonly added to natural rubber during vulcanization is sulphur, which forms cross links between polymer chains and improves strength and elasticity.