Problem 6 - A Complete Resource Book in Chemistry for JEE Main

Question

Which gas is liberated, when alkaline formaldehyde solution is treated with \(\mathrm{H}_{2} \mathrm{O}_{2} ?\) (a) \(\mathrm{CH}_{4}\) (b) \(\mathrm{H}_{2}\) (c) \(\mathrm{CO}_{2}\) (d) \(\mathrm{O}_{2}\)

Step-by-Step Solution

Answer

Oxygen gas (\(\mathrm{O}_2\)) is liberated.

Step 1: Understand the Reaction Setup

The problem involves treating an alkaline solution of formaldehyde with hydrogen peroxide (\(\mathrm{H}_2\mathrm{O}_2\)). "Alkaline formaldehyde solution" suggests formaldehyde (\(\mathrm{CH}_2\mathrm{O}\) or \(\mathrm{HCHO}\)) in a basic medium.

Step 2: Determine the Type of Reaction

In an alkaline medium, \(\mathrm{H}_2\mathrm{O}_2\) acts both as an oxidizing agent and can decompose, especially in the presence of reducible substances like formaldehyde. We expect some redox activity in this setup.

Step 3: Identify the Redox Reaction

Hydrogen peroxide can decompose in alkaline conditions to form oxygen gas and water: \[ 2\mathrm{H}_2\mathrm{O}_2 \rightarrow 2\mathrm{H}_2\mathrm{O} + \mathrm{O}_2 \] Formaldehyde can undergo further reactions, but the key note is that \(\mathrm{O}_2\) is liberated from the decomposition of \(\mathrm{H}_2\mathrm{O}_2\).

Step 4: Confirm the Liberated Gas

In the setup, while formaldehyde is present, the action and nature of \(\mathrm{H}_2\mathrm{O}_2\) in alkaline conditions prominently leads to the liberation of \(\mathrm{O}_2\) gas from its own decomposition.

Key Concepts

Formaldehyde Chemistry

Formaldehyde is a simple yet important organic compound with the formula \(\mathrm{CH}_2\mathrm{O} \) or \( \mathrm{HCHO} \). It is an example of an aldehyde, characterized by a carbon atom double-bonded to an oxygen atom, also known as a carbonyl group. In the context of formaldehyde chemistry, it serves diverse roles depending on its environment:

• In basic media, such as when dissolved in alkaline solutions, formaldehyde can engage in various chemical reactions due to its reactivity.
• Being a versatile participant, it is often employed in synthesis and reactions where its carbonyl group can be transformed or facilitated into further reactions.

Notably, in these reactions, formaldehyde can act as a reducing agent, meaning it can donate electrons to other substances during a chemical process. This characteristic is significant, especially when discussing redox reactions.

Redox Reactions

Redox reactions stand for oxidation-reduction reactions, which are fundamental chemical processes where the transfer of electrons occurs between two species. These reactions are characterized by one species undergoing oxidation (loss of electrons) and another reduction (gain of electrons). When investigating the reaction of formaldehyde in an alkaline environment with hydrogen peroxide, redox dynamics are at play.

Hydrogen peroxide (\(\mathrm{H}_2\mathrm{O}_2\)) can act as both:

• An oxidizing agent: It can accept electrons from another substance, undergoing reduction itself.
• A reducible substrate: It can also decompose, releasing oxygen gas in basic conditions.

In the presence of formaldehyde, hydrogen peroxide facilitated the redox process leading to the eventual liberation of \(\mathrm{O}_2 \) gas, showcasing its dual behavior within the reaction setup.

Decomposition Reactions

Decomposition reactions are a type of chemical reaction where a single compound breaks down into two or more simpler substances. These reactions are crucial in understanding the behavior of compounds like hydrogen peroxide under different conditions.

In the exercise, we look at hydrogen peroxide in an alkaline medium:

• Upon introduction to the alkaline environment, \(\mathrm{H}_2\mathrm{O}_2\) can spontaneously decompose.
• The reaction: \(2\mathrm{H}_2\mathrm{O}_2 \rightarrow 2\mathrm{H}_2\mathrm{O} + \mathrm{O}_2\) illustrates how hydrogen peroxide splits into water and oxygen gas.

This decomposition is enhanced in the presence of reactive substances like formaldehyde. Such reactions are particularly noteworthy in experimental setups, providing insight into the reactivity patterns of hydrogen peroxide in different chemical environments.