Problem 91 - Advanced Problems in Organic Chemistry for Competitive Examinations

Question

Aqueous solution of which of the following compounds is electrolysed, when acetylene gas is obtained? (a) Sodium fumerate (b) Sodium maleate (c) Sodium acetate (d) Calcium carbide

Step-by-Step Solution

Answer

Calcium carbide (d) produces acetylene gas during electrolysis.

Step 1: Analyzing the compounds possibilities

To find out which compound gives acetylene gas upon electrolysis in aqueous solution, we first need to understand how each of these compounds behave when dissolved in water and subjected to electrolysis.

Step 2: Understanding Acetylene Formation Process

Acetylene (C₂H₂) gas can be generated by the reaction of water with calcium carbide (CaC₂). The reaction is \[ \text{CaC}_2 + 2\text{H}_2\text{O} \rightarrow \text{C}_2\text{H}_2 + \text{Ca(OH)}_2 \] It is important to note that sodium compounds like fumerate, maleate, and acetate do not participate in reactions producing acetylene under electrolysis.

Step 3: Identifying the Correct Compound

Given the observation from Step 2, we can deduce that calcium carbide when reacted with water produces acetylene gas. Therefore, it must be the compound that yields acetylene gas during electrolysis in an aqueous solution.

Key Concepts

Acetylene Formation

Acetylene, a simple alkyne with the molecular formula \(\text{C}_2\text{H}_2\), is an essential building block in organic chemistry. It is a highly flammable gas, widely recognized for its use in welding due to its ability to produce a very hot flame. But where does it come from? Acetylene is formed through a specific reaction involving calcium carbide and water. This reaction is typically utilized in industrial settings to produce acetylene on a large scale.

• Acetylene is a colorless and explosive gas often stored dissolved in acetone for safety.
• In organic chemistry, acetylene is used as a precursor for synthesizing various other organic compounds.
• Its formation from calcium carbide is not just important in chemistry labs but also has historical significance as one of the earlier methods of producing acetylene.

Knowing how acetylene is produced helps in understanding its applications and safety precautions when using it in any setting.

Calcium Carbide Reaction

The reaction between calcium carbide (CaC₂) and water is a crucial chemical process for producing acetylene gas. This fascinating reaction can be illustrated by the chemical equation:\[ \text{CaC}_2 + 2\text{H}_2\text{O} \rightarrow \text{C}_2\text{H}_2 + \text{Ca(OH)}_2 \]Here's how it unfolds:

• When calcium carbide comes into contact with water, an immediate chemical reaction occurs, releasing acetylene gas and forming calcium hydroxide as a by-product.
• This reaction is highly exothermic, meaning it releases heat, which is why it needs to be carefully controlled in industrial environments.
• Calcium carbide is typically stored in sealed containers to prevent unwanted reactions with moisture from the air.

Understanding this reaction process is vital for industries that rely on acetylene for processes such as cutting, welding, and chemical synthesis.

Aqueous Electrolysis Processes

Electrolysis is a chemical process that uses an electric current to drive a non-spontaneous chemical reaction. In the context of organic compounds, particularly those in aqueous solutions, electrolysis can lead to various products, depending on the compounds involved.

• Not all compounds produce acetylene when electrolyzed in aqueous solutions. For example, sodium fumerate, sodium maleate, and sodium acetate do not produce acetylene via electrolysis.
• The focus is on calcium carbide because when it interacts with water, it directly leads to acetylene formation, as opposed to the sodium compounds mentioned.
• During electrolysis, ions present in the solution are subjected to redox reactions, which can lead to a wide array of chemical transformations.

Electrolysis is instrumental in both laboratory and industrial settings, providing a means to produce specific chemicals efficiently, making it a versatile tool in electrochemical synthesis.