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 (d) \(\mathrm{CH}_2=\mathrm{CH}\mathrm{Cl}\).

Step 1: Understand the Definition of a Monomer

A monomer is a small molecule that can bind chemically to other molecules to form a polymer. Polyvinyl chloride (PVC) is a widely used polymer.

Step 2: Know the Structure of Polyvinyl Chloride

Polyvinyl chloride (PVC) is composed of repeating units derived from vinyl chloride monomers. The chemical formula of vinyl chloride is C2H3Cl or, in expanded form, CH2=CHCl.

Step 3: Identify the Correct Monomer from the Options

Given the options, we need to choose the molecular formula that represents the monomer of PVC, which we found to be CH2=CHCl. Review each option: (a) CH3-CH2Cl, (b) CH2=CH2, (c) CHCl=CHCl, (d) CH2=CHCl.

Step 4: Select the Correct Answer

Compare the known formula for the monomer of PVC (CH2=CHCl) with the provided options. Option (d) is CH2=CHCl, which matches the known monomer formula for vinyl chloride.

Key Concepts

Monomers in Polymers

A monomer is a fundamental concept in polymer science. It is a small molecule capable of bonding with other similar molecules to form a long chain or network known as a polymer. The process of forming these large structures is called polymerization, and it occurs when monomers repeatedly react with each other.

Understanding monomers is crucial as they determine the structure and properties of the resulting polymer. For example, if you consider polyvinyl chloride (PVC), its desirable characteristics such as flexibility, durability, and resistance to environmental conditions stem from the nature of its monomer unit - vinyl chloride. These properties make PVC useful in everyday products like pipes, wires, and clothing. By studying monomers, we understand the building blocks that create polymers' variety and utility.

Vinyl Chloride Structure

Vinyl chloride is a simple molecule yet it plays a vital role in the structure of polyvinyl chloride (PVC). Its chemical formula is \( \mathrm{C_2H_3Cl} \) or, written in a more detailed format, \( \mathrm{CH_2=CHCl} \). This structure displays a double bond between carbon atoms, which is essential for polymerization.

Breaking it down further, the structure includes:

• Two carbon atoms (C)
• Three hydrogen atoms (H)
• One chlorine atom (Cl)

The presence of the chlorine atom is key to the functionality and properties of vinyl chloride. The chlorine gives vinyl chloride its unique reactivity, contributing to the rigidity and stability of PVC. When these monomer units connect, they form the durable and versatile polyvinyl chloride material. Vinyl chloride's simple yet distinct composition shows how even small variations in a molecule's makeup can lead to diverse material properties.

Chemical Formulas in Chemistry

Chemical formulas are shorthand representations of chemical compounds. They reveal significant information about the types and numbers of atoms in a molecule. In chemistry, understanding these formulas is essential for studying substance composition and reactions.

Within chemical formulas, elements are represented by their chemical symbols, followed by a subscript showing the number of each type of atom. For instance, in polyvinyl chloride's monomer, \( \mathrm{CH_2=CHCl} \), we know:

• The symbols \( \mathrm{CH_2} \) and \( \mathrm{CHCl} \) indicate the presence of two carbon atoms and one chlorine atom.
• The numeric subscripts denote the number of hydrogen atoms linked to each respective carbon atom.

Chemical equations, such as the polymerization reaction involving vinyl chloride, use these formulas to provide essential insight into how materials interact at the molecular level. Mastering the interpretation of chemical formulas enables chemists to predict the outcomes of reactions and design new materials with desired properties.