Problem 112 - A Complete Resource Book in Chemistry for JEE Main

Question

Oxalic acid is heated with concentrated \(\mathrm{H}_{2} \mathrm{SO}_{4}\). When the resultant gases are passed over red hot carbon, \(X\) is obtained. \(X\) is (a) \(\mathrm{CO}\) (b) \(\mathrm{CO}_{2}\) (c) \(\mathrm{C}_{2} \mathrm{H}_{4}\) (d) \(\mathrm{CH}_{4}\)

Step-by-Step Solution

Answer

The compound \(X\) is carbon monoxide \(\mathrm{CO}\), which is option (a).

Step 1: Understanding the reaction of oxalic acid and sulfuric acid

When oxalic acid (\[ \text{H}_2\text{C}_2\text{O}_4 \] ) is heated with concentrated sulfuric acid (\[ \text{H}_2\text{SO}_4 \] ), a dehydration reaction occurs, resulting in the formation of carbon monoxide (\[ \text{CO} \] ) and carbon dioxide (\[ \text{CO}_2 \] ) as the main gases.

Step 2: Reacting the gases with red hot carbon

The resultant gases, which are carbon monoxide and carbon dioxide, are then passed over red hot carbon. Carbon dioxide reacts with carbon to produce carbon monoxide according to the reaction: \[ \text{CO}_2 + \text{C} \rightarrow 2\text{CO} \]. Thus, the main product formed is carbon monoxide (\(\text{CO}\)).

Step 3: Identifying compound \(X\)

As per the reaction, when both \(\text{CO}_2\) is completely converted, the final product \(X\) obtained is carbon monoxide (\(\text{CO}\)). Therefore, \(X\) corresponds to option (a).

Key Concepts

Oxalic Acid

Oxalic acid is an organic compound with the formula \( ext{H}_2 ext{C}_2 ext{O}_4\). It is a type of dicarboxylic acid, which means it has two carboxyl groups (-COOH) attached. Oxalic acid is naturally found in many plants, such as rhubarb and spinach. When it is heated, it tends to decompose into simpler molecules.
In chemical reactions, oxalic acid often acts as a reducing agent, meaning it donates electrons during the reaction. When combined with concentrated sulfuric acid, it undergoes dehydration, leading to the release of gases including carbon monoxide \( ext{CO}\) and carbon dioxide \( ext{CO}_2\). These reactions are significant in understanding how organic acids break down when subjected to heat and strong acids.
Given its potential for decomposition, handling oxalic acid requires caution, especially since its breakdown can release the toxic gas carbon monoxide.

Sulfuric Acid

Sulfuric acid, having the chemical formula \( ext{H}_2 ext{SO}_4\), is a highly corrosive and strong mineral acid. It is widely used in laboratories and industry due to its excellent dehydrating properties. Here are some important characteristics of sulfuric acid:

• It acts as a dehydrating agent, meaning that it can remove water (\( ext{H}_2 ext{O}\)) from compounds.
• It is a strong acid, dissociating completely in water to release hydrogen ions (\( ext{H}^+\)) and sulfate ions (\( ext{SO}_4^{2-}\)).
• It can cause severe chemical burns and should be handled with care.

When sulfuric acid is used with oxalic acid, it promotes the decomposition of oxalic acid by pulling out water, ultimately leading to the formation of gases like carbon monoxide and carbon dioxide. This specific reaction showcases how sulfuric acid can drive complex chemical processes by altering the chemical structure of substances through dehydration.

Carbon Monoxide

Carbon monoxide is a colorless, odorless gas with the molecular formula \( ext{CO}\). It is a product of incomplete combustion and certain chemical reactions, including the breakdown of oxalic acid in the presence of sulfuric acid and hot carbon. Here are some key characteristics of carbon monoxide:

• It is highly toxic, as it can bind to hemoglobin in the blood, preventing proper oxygen transport.
• It is flammable and can produce more heat than carbon dioxide when combusted, which is why it has some industrial uses.
• The production of CO can occur naturally in processes like volcanic eruptions or be a result of human activity, such as vehicle emissions.

In chemical reactions, carbon monoxide often serves as a reducing agent. Its ability to bond with metals and other compounds makes it a versatile molecule in various industrial applications.
The understanding of how carbon monoxide is formed and used highlights its importance in both chemical reactions and environmental considerations.