Question

The monomer used for the manufacture of PVC is obtained by the addition of (a) \(\mathrm{Cl}_{2}\) to ethylene (b) \(\mathrm{Cl}_{2}\) to acetylene (c) HCl to ethylene (d) HCl to acetylene in presence of \(\mathrm{Hg}^{2+}\) salts

Short answer

The monomer for PVC is obtained by adding HCl to acetylene with Hg²⁺ salts (option d).

Step-by-step solution

Understanding PVC Production

PVC, or polyvinyl chloride, is a polymer that is manufactured from a specific monomer. The monomer used for PVC is vinyl chloride (CH2=CHCl). This monomer is obtained through specific chemical reactions involving simpler molecules.

Identifying the Monomer

Vinyl chloride can be produced in several ways. One common industrial method involves the addition of HCl to acetylene (C2H2) in the presence of mercuric chloride (HgCl2) as a catalyst, which forms vinyl chloride. This method is historically significant in the production of PVC.

Examining the Options

Let's analyze the given options: (a) and (c) involve reactions with ethylene, which do not readily produce vinyl chloride directly. Option (b) involves adding Cl2 to acetylene, which leads to a dichloro compound, not vinyl chloride. Option (d) involves the addition of HCl to acetylene in the presence of mercuric salts, which is precisely the reaction that produces vinyl chloride.

Selecting the Correct Answer

After examining all options and identifying the correct chemical process that forms vinyl chloride, the correct answer is option (d) because it describes the correct method of producing the vinyl chloride monomer used for PVC.

Key concepts

Vinyl Chloride

Vinyl chloride, with the chemical formula \( ext{CH}_2= ext{CHCl}\), is an essential compound used in the production of polyvinyl chloride, commonly known as PVC. PVC is one of the world's most used plastics, found in a variety of products from pipes to credit cards. Vinyl chloride acts as the building block or monomer for PVC, undergoing a process called polymerization where thousands of these monomer molecules join together to form the long chains that make up the plastic material. This compound is typically a colorless gas under standard conditions and has a sweet odor at high concentrations.
Given its role in industrial applications, understanding how vinyl chloride is produced is crucial for students studying chemistry or industrial processes. Often, industries produce vinyl chloride by adding HCl to acetylene—a method that will be detailed in subsequent sections. The polymerization of vinyl chloride into PVC is a key step that utilizes the properties of vinyl chloride to create materials suited for numerous applications.

Acetylene

Acetylene is a simple alkyne, a hydrocarbon compound featuring a carbon-carbon triple bond, giving it the formula \( ext{C}_2 ext{H}_2\). It is known for being a colorless gas with a faintly sweet smell and is quite flammable, which makes it useful in applications such as welding. The triple bond in acetylene makes it incredibly reactive, enabling it to undergo various chemical reactions.
In the context of PVC production, acetylene is a critical starting material. It serves as the backbone for the eventual formation of vinyl chloride. The reactivity of acetylene allows it to undergo addition reactions, which are vital in transforming acetylene into more complex compounds like vinyl chloride. When hydrochloric acid is added to acetylene in the presence of specific catalysts, the acetylene molecule accepts the additional elements to transform into vinyl chloride. This step is crucial in establishing the right structure for vinyl chloride and hence PVC.

HCl Addition

The process of HCl addition involves a chemical reaction where hydrochloric acid (HCl) is added to another compound. In PVC production, this step involves acetylene reacting with HCl. The formula of hydrochloric acid is \( ext{HCl}\), and it plays a pivotal role in transforming acetylene into vinyl chloride.
This reaction is of particular interest due to its historical significance in industrial processes. When HCl is added to acetylene, the result is the production of vinyl chloride, which is the main monomer for PVC. This transformation is not spontaneous and requires the presence of a catalyst to proceed efficiently. The addition of HCl brings about the structural changes in acetylene needed to form the vinyl chloride, making this process a cornerstone in PVC manufacturing. Understanding the chemistry behind this reaction enables students to comprehend how simple molecules can interact to form essential industrial compounds.

Catalysis with Mercuric Chloride

Catalysis is a process where the rate of a chemical reaction is increased by a substance called a catalyst, which is not consumed in the reaction. In the production of PVC, mercuric chloride (\( ext{HgCl}_2\)) acts as a catalyst. It facilitates the addition of HCl to acetylene, enabling the formation of vinyl chloride.
The role of mercuric chloride in this reaction is substantial, as it helps to enable the otherwise slow interaction between acetylene and HCl. By providing a surface or environment where reactions occur more readily, catalysts like mercuric chloride lower the energy needed for the reaction. This efficiency is vital in a large-scale industrial setting, where the quick and cost-effective production of vinyl chloride is essential. Understanding catalysis with mercuric chloride allows students to appreciate the importance of catalysts in chemistry and industry, offering deeper insights into how industrial processes are optimized for efficiency and economic viability.