Problem 42 - A Complete Resource Book in Chemistry for JEE Main

Question

The monomer unit of polyvinyl chloride has the formula (a) \(\mathrm{CH}_{3}-\mathrm{CH}_{2} \mathrm{Cl}\) (b) \(\mathrm{CH}_{2}=\mathrm{CH}_{2}\) (c) \(\mathrm{CHCl}=\mathrm{CHCl}\) (d) \(\mathrm{CH}_{2}=\mathrm{CHCl}\)

Step-by-Step Solution

Answer

The monomer unit of polyvinyl chloride is \( \mathrm{CH}_{2} = \mathrm{CHCl} \).

Step 1: Identify the Polymer

Polyvinyl chloride (PVC) is a polymer that is commonly used in a variety of applications. To understand the monomer unit of PVC, we first need to recognize what PVC actually is. PVC is made by the polymerization of vinyl chloride monomers.

Step 2: Examine Possible Monomer Structures

Given the options, identify which one represents vinyl chloride. Vinyl chloride is known to have a double bond between carbon atoms and a chlorine atom attached to the ethylene molecule, which best fits the structure.

Step 3: Match with Vinyl Chloride Structure

The molecular formula of vinyl chloride is \( \mathrm{CH}_{2} = \mathrm{CHCl} \), which consists of a double bond between the two carbon atoms and one chlorine atom directly connected to one of these carbon atoms.

Step 4: Conclude the Correct Answer

From the analysis of the options, the formula \( \mathrm{CH}_{2} = \mathrm{CHCl} \) corresponds to vinyl chloride, the monomer unit of polyvinyl chloride.

Key Concepts

Monomer Unit

A monomer unit is a basic building block of a polymer. Polymers are large molecules composed of repeated monomer units, which are held together by covalent chemical bonds. In the case of polyvinyl chloride (PVC), the monomer unit is vinyl chloride. Understanding monomer units is crucial because the properties of a polymer largely depend on its monomer constituents. The physical, chemical, and mechanical properties of polymers can be traced back to their monomer configurations. When we want to create PVC, we repeatedly link vinyl chloride monomers through a chemical process known as polymerization. This repetitive linking is what enables the construction of a complex polymer structure from simple monomer units.

Vinyl Chloride

Vinyl chloride is an organic compound that serves as the monomer for polyvinyl chloride (PVC). Its molecular structure is denoted as \( \mathrm{CH}_{2}=\mathrm{CHCl} \). This structure features a double bond between two carbon atoms, and a chlorine atom attached to one of these carbons.
Vinyl chloride itself is a colorless gas, known for its role in the production of PVC.

• High reactivity due to the presence of a double bond.
• Contains both carbon and chlorine atoms, contributing to PVC’s unique characteristics.
• Utilized predominantly in manufacturing PVC, a highly versatile material.

Understanding vinyl chloride is essential since its incorporation into a polymer leads to a wide array of commercial and industrial applications, from pipes and cables to clothing and furniture.

Polymerization

Polymerization is the chemical process that combines monomer units into a polymer. For PVC production, the polymerization of vinyl chloride is essential.
In the case of vinyl chloride, a process called "addition polymerization" occurs. This means each monomer adds to the chain, connecting through the reactive centers at the double bond to form lengthy, repeating chains.
Replacement of the double bond in each monomer with single bonds leads to the formation of long polymer chains.

• The process is initiated by heat, light, or a catalyst.
• Creates a tightly bound chain of vinyl chloride units.
• Enables mass production of PVC in different forms and grades for various uses.

Polymerization is crucial because it not only establishes the polymer framework but also changes the behavior and characteristics of the resulting material, PVC, enhancing its practicality for countless applications.

Chemical Formula

The chemical formula plays a central role in understanding any compound. It is a simplified representation of the molecule’s composition using elemental symbols and numerical subscripts.
For vinyl chloride, the chemical formula \( \mathrm{CH}_{2}=\mathrm{CHCl} \) specifically reflects:

• Two carbon atoms (\( \mathrm{C}\)) bonded with a double bond.
• Three hydrogen atoms (\( \mathrm{H}\)) distributed among the carbons.
• One chlorine atom (\( \mathrm{Cl}\)) attached to one of the carbons.

This formula is significant in identifying the unique properties of vinyl chloride, impacting the characteristics and functionalities of polyvinyl chloride (PVC). Understanding the chemical formula provides an insightful glimpse into the reactivity and molecular interaction that define the material properties of PVC.