Problem 2 - Chemistry in 30 days

Question

Sodium benzoate on heating with soda lime gives: (a) Benzenc (b) Methane (c) Calcium benzoate (d) Toluene

Step-by-Step Solution

Answer

Sodium benzoate on heating with soda lime gives benzene (option a).

Step 1: Understanding the Reaction

When sodium benzoate is heated with soda lime (a mixture of NaOH and CaO), it undergoes decarboxylation. Decarboxylation is a chemical reaction in which a carboxyl group (-COOH) is removed from a molecule, often releasing carbon dioxide (CO₂). This process results in the formation of a hydrocarbon.

Step 2: Identify the Product

The decarboxylation of sodium benzoate using soda lime results in the removal of the carboxyl group from the benzoate ion. The compound that remains after removing the -CO₃ group from sodium benzoate is benzene (C₆H₆).

Step 3: Equation of the Reaction

The chemical equation for the reaction can be written as:\[ ext{C₆H₅COONa + NaOH} ightarrow ext{C₆H₆ + Na₂CO₃}\]This equation shows that sodium benzoate when heated with soda lime produces benzene and sodium carbonate.

Step 4: Verify the Options

Given the multiple-choice options, check which one corresponds to benzene. The options are: (a) Benzene, (b) Methane, (c) Calcium benzoate, (d) Toluene.

Step 5: Select the Correct Option

Based on the analysis and the chemical reaction described, the answer to the reaction of sodium benzoate with soda lime is option (a) Benzene.

Key Concepts

Sodium Benzoate

Sodium benzoate is a commonly used compound in various chemical and industrial applications. It is the sodium salt of benzoic acid. One of its key roles is as a preservative in food, where it inhibits the growth of mold, yeast, and some bacteria, ensuring longer shelf life. When discussing sodium benzoate in a chemical reaction context, it serves as a reactant where a transformation occurs under specific conditions.
In the process of decarboxylation, where sodium benzoate is heated with soda lime, its structure undergoes change. The benzoate ion part of sodium benzoate, which contains a carboxyl group, loses this group as carbon dioxide. This leaves behind a different compound, typically a hydrocarbon. Understanding this chemical behavior is important in organic chemistry, especially in processes where removal of carboxyl groups is necessary.

Soda Lime

Soda lime is a crucial component in the decarboxylation reaction of sodium benzoate. It is a mixture of sodium hydroxide (NaOH) and calcium oxide (CaO). This blend is highly effective in absorbing carbon dioxide, but in this reaction, it contributes to the successful removal of the carboxyl group from sodium benzoate.

• Sodium hydroxide, a strong base, reacts with sodium benzoate to trigger the decarboxylation process.
• Calcium oxide serves as a stabilizing agent and can help in ensuring that the reaction proceeds smoothly without unintended side reactions.

Heating this mixture is essential, as it provides the necessary energy for the reaction to occur, leading to the production of benzene from sodium benzoate. Understanding the role of soda lime helps us appreciate its usage beyond just a basic chemical compound, especially in organic synthesis and various industrial applications.

Chemical Reaction

A chemical reaction is a process in which one or more substances are converted into new substances. The scenario of sodium benzoate reacting with soda lime involves a chemical transformation known as decarboxylation:

• The reaction specifically targets the removal of a carboxyl group, resulting in the evolution of carbon dioxide.
• This conversion leads to the formation of a simpler molecule, usually a hydrocarbon.

In our case, the initial reactants are sodium benzoate and soda lime, and through the reaction, these are transformed into benzene and sodium carbonate. The balanced chemical equation representing this is:\[ \text{C}_6\text{H}_5\text{COONa} + \text{NaOH} \rightarrow \text{C}_6\text{H}_6 + \text{Na}_2\text{CO}_3 \]\This equation shows how the loss of the -COO part of the sodium benzoate leads to benzene formation, highlighting the reaction type and products.

Benzene

Benzene is the result of the decarboxylation of sodium benzoate using soda lime. It is a simple aromatic hydrocarbon, characterized by its ring structure composed of six carbon atoms with alternating double bonds. Benzene, with the formula \(\text{C}_6\text{H}_6\), is a fundamental building block in organic chemistry and is widely used as a precursor to various chemicals and materials.
Due to its structure, benzene serves as a foundation in the petrochemical industry, with applications in producing plastics, resins, synthetic fibers, and rubber. However, it is important to note that benzene is a known carcinogen, prompting careful handling and use in controlled environments.
Understanding how benzene is formed through reactions like decarboxylation helps chemists harness its properties while applying precautions to mitigate its risks, promoting safe usage in laboratory and industrial settings.