Target Exam

CUET

Subject

Chemistry

Chapter

Organic: Aldehydes, Ketones and Carboxylic Acids

Question:

Benzoic acid is almost insoluble in which of the following solvents?

Options:

Ether

Alcohol

Cold water

Benzene

Correct Answer:

Cold water

Explanation:

The correct answer is option 3. Cold water.

Why Benzoic Acid Hates Cold Water

Benzoic acid ($C_6H_5COOH$) consists of two main parts:

  1. The Benzene Ring ($C_6H_5$): This is a large, non-polar hydrocarbon group that is "hydrophobic" (water-fearing).
  2. The Carboxyl Group ($-COOH$): This part is polar and can form hydrogen bonds with water.

In cold water, the large non-polar benzene ring dominates the molecule's behavior. The water molecules would rather stay hydrogen-bonded to each other than break apart to surround the bulky, non-polar ring. This makes the acid almost insoluble at room temperature or below.

Comparison with Other Solvents

Solvent

Solubility Level

Reason

Ether

High

Both are organic and share similar intermolecular forces.

Alcohol

High

Ethanol has a non-polar tail that interacts well with the benzene ring.

Benzene

High

Non-polar dissolves non-polar; they are structurally very similar.

Hot Water

Moderate

As temperature increases, kinetic energy helps break the intermolecular bonds, allowing it to dissolve better than in cold water.

Summary

Benzoic acid prefers organic solvents (like options 1, 2, and 4) because it is largely non-polar.  

It dissolves in water only reluctantly, and that too when the temperature is increased.