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, \(\mathrm{X}\) is obtained. \(\mathrm{X}\) is (a) \(\mathrm{CO}\) (b) \(\mathrm{CO}_{2}\) (c) \(\mathrm{C}_{2} \mathrm{H}_{4}\) (d) \(\mathrm{CH}_{4}\)

Step-by-Step Solution

Answer

X is carbon monoxide (CO).

Step 1: Identify Reaction of Oxalic Acid with Concentrated Sulfuric Acid

When oxalic acid \((\mathrm{H}_2\mathrm{C}_2\mathrm{O}_4)\) is heated with concentrated \(\mathrm{H}_{2} \mathrm{SO}_{4}\), it decomposes to form carbon monoxide \((\mathrm{CO})\), carbon dioxide \((\mathrm{CO}_2)\), and water \((\mathrm{H}_2\mathrm{O})\). This is represented by the chemical equation: \[ \mathrm{H}_2\mathrm{C}_2\mathrm{O}_4 \rightarrow \mathrm{CO} + \mathrm{CO}_2 + \mathrm{H}_2\mathrm{O} \] This means after the reaction, both \(\mathrm{CO}\) and \(\mathrm{CO}_2\) gases are liberated.

Step 2: Pass Resultant Gases over Red Hot Carbon

The next step is to pass the gases \(\mathrm{CO}\) and \(\mathrm{CO}_2\) over red-hot carbon. When carbon dioxide \((\mathrm{CO}_2)\) reacts with hot carbon, carbon monoxide \((\mathrm{CO})\) is produced. This reaction can be represented as: \[ \mathrm{CO}_2 + C \rightarrow 2\mathrm{CO} \] This reaction converts any \(\mathrm{CO}_2\) present into additional \(\mathrm{CO}\).

Key Concepts

Oxalic Acid

Oxalic acid is an organic compound, often found naturally in plants like spinach and rhubarb. Its chemical formula is \( \mathrm{H}_2\mathrm{C}_2\mathrm{O}_4 \), and it belongs to a family of compounds known as dicarboxylic acids, which have two carboxyl groups \(-COOH\).
Oxalic acid is known for its ability to form strong hydrogen bonds and can easily coordinate with metal ions.
In many chemical reactions, it plays an important role due to its acidic nature and is often used in rust removal and cleaning agents.

• Oxalic acid readily donates protons due to its carboxyl groups.
• It forms various coordination compounds with metals.
• In concentrated forms, it's a powerful reducing agent.

Oxalic acid is also used industrially for bleaching and metal cleaning due to these reductive capabilities.

Sulfuric Acid

Sulfuric acid, or \( \mathrm{H}_2\mathrm{SO}_4 \), is a highly corrosive strong mineral acid. It's one of the most important industrial chemicals and is used in a wide range of applications including fertilizer production and chemical synthesis.
Due to its highly exothermic reaction with water, it serves as an efficient dehydrating agent.
This property makes it useful for removing water molecules from various compounds, which is evident in its reaction with oxalic acid.

• Highly corrosive and strong acidic nature.
• Used as a drying agent in many chemical processes.
• In concentrated form, it effectively dehydrates compounds.

During heating, sulfuric acid can decompose certain organic acids, such as oxalic acid, by extracting water molecules, thus aiding in their decomposition.

Carbon Monoxide Production

Carbon monoxide \( \mathrm{CO} \) is a colorless and odorless gas produced through the incomplete combustion of carbon-containing materials.
In the reaction involving oxalic acid and sulfuric acid, carbon monoxide is one of the decomposition products.
When the resultant gases (carbon monoxide and carbon dioxide) are passed over red-hot carbon, more carbon monoxide is produced by the reaction of carbon dioxide with carbon.

• Produced from incomplete combustion or decomposition reactions.
• Often found in environments where combustion occurs but oxygen is limited.
• Dangerous due to its ability to bind with hemoglobin more effectively than oxygen.

The ability to convert carbon dioxide into carbon monoxide by reacting it with carbon under high heat showcases an important transformation that has been utilized in industrial processes.

Decomposition Reactions

Decomposition reactions involve a single compound breaking down into two or more simpler substances. These reactions are common in various chemical and biological processes.
For oxalic acid, its decomposition in the presence of sulfuric acid is represented by the breakdown into carbon monoxide, carbon dioxide, and water.

• These reactions often require energy input, such as heat, to proceed.
• They are important in both producing simpler substances and understanding stability.
• Decomposition is also a key step in recycling and waste management processes.

This concept is fundamental in chemistry as it helps explain how complex molecules can be broken into more manageable components.