Problem 1 - Arihant Objective Approach to Organic Chemistry for IIT JEE and NEET all Medical Entrances Part 4

Question

The bakelite is prepared by the reaction between: (a) urea and formaldehyde (b) phenol and formaldehyde (c) ethylene glycol (d) tetramethylene glycol

Step-by-Step Solution

Answer

Bakelite is prepared by the reaction between phenol and formaldehyde (option b).

Step 1: Identify Components of Bakelite

Bakelite is a type of plastic that is known as a phenolic resin. It is commonly used in electrical insulators and radio and telephone casings due to its good insulating properties and heat resistance.

Step 2: Determine Key Reactants

Bakelite is specifically synthesized through a condensation reaction involving phenol and formaldehyde. This reaction involves the combination of these two chemicals under heat, resulting in a hard, thermosetting polymer.

Step 3: Analyze Options

Go through the provided options: (a) urea and formaldehyde, (b) phenol and formaldehyde, (c) ethylene glycol, (d) tetramethylene glycol. Option (b) contains phenol and formaldehyde, which matches the known reactants for creating bakelite.

Step 4: Verify the Correctness

Confirm that option (b) is the correct choice by recalling that phenolic resins, like bakelite, have a base chemical composition primarily involving phenol and formaldehyde. The other options do not contain both these necessary components.

Key Concepts

Phenolic Resins

Phenolic resins, a major component in the production of Bakelite, were one of the first synthetic polymers ever created. These resins are formed primarily from phenol, an organic compound, and formaldehyde, a simple aldehyde. Phenolic resins are valued for their strength, thermal stability, and insulating properties. They're commonly used in various industries:

• Electronics for circuit boards and insulators
• Automotive for brake linings and parts
• Household products like kitchenware

Phenolic resins come in two forms: novolacs and resoles.
Novolacs remain stable until hardeners are added, while resoles can harden on their own when heated. This versatility makes them particularly useful in industrial applications.

Condensation Reaction

The synthesis of Bakelite is a classic example of a condensation reaction. A condensation reaction occurs when two molecules combine to form a single molecule, producing a small molecule as a byproduct, often water, in the process. In the case of Bakelite, the reaction involves phenol and formaldehyde. Under heat, these reactants form a network polymer, releasing water as a byproduct.
This type of reaction essentially builds up larger and more complex structures from simpler molecules. The release of byproducts like water signifies the transition from individual small molecules to a solid network polymer, contributing to Bakelite's robust physical properties.
Understanding this reaction helps us appreciate the science behind how materials like Bakelite gain their useful characteristics such as high thermal resistance and electrical insulation.

Thermosetting Polymer

Bakelite belongs to a category of polymers known as thermosetting polymers. These polymers are unique because once they are shaped and solidified, they cannot be remelted or reshaped. This behavior results from their cross-linked structure formed during polymerization, which imparts high structural integrity and resistance to high temperatures and chemicals.

• These polymers do not soften upon heating.
• Because of their rigid structure, they are used in high-stress environments such as electrical insulating materials.
• They are also more brittle compared to thermoplastics, which can be remelted and reshaped.

The thermosetting nature of Bakelite makes it highly valuable in industrial applications where durability and resistance to heat and electricity are crucial.