With reference to industrial chemical agents and cleansing compounds used in daily life, c… — State PSC Exam

With reference to industrial chemical agents and cleansing compounds used in daily life, consider the following statements:

1. Calcium hypochlorite ( $CaOCl_2$ ), commonly known as bleaching powder, acts as a bleaching agent primarily due to the liberation of nascent oxygen upon reaction with dilute acids or atmospheric carbon dioxide.
2. Hard water reduces the cleansing efficiency of soaps by reacting with sodium or potassium salts of fatty acids to form insoluble calcium and magnesium precipitates.
3. Synthetic detergents containing highly branched-chain alkyl benzene sulfonates are readily biodegradable by microorganisms compared to linear alkyl chain detergents.

Which of the statements given above is/are correct?

1 and 2 onlyAnswer
B
2 and 3 only
C
1 and 3 only
D
1, 2 and 3

Answer

The correct option is the one stating that statements 1 and 2 only are correct.

Statements 1 and 2 accurately describe fundamental chemical processes: bleaching powder releases nascent oxygen which acts as a powerful oxidizing bleach, and hard water containing dissolved calcium and magnesium ions precipitates fatty acid salts of soaps. Statement 3 is false because highly branched alkyl chains resist microbial breakdown, whereas straight/linear alkyl chain detergents are readily biodegradable.

Step-by-Step Solution

Analyze statement 1 regarding bleaching powder mechanism

Bleaching powder (

CaOCl_2

) reacts with dilute acid or atmospheric

CO_2

to release hypochlorous acid (

HOCl

), which decomposes to liberate nascent oxygen (

[O]

). The nascent oxygen oxidizes colored organic matter into colorless compounds. Thus, statement 1 is correct.

Bleaching action of chlorine-based bleaches depends on oxidation via nascent oxygen.

Analyze statement 2 regarding soap behavior in hard water

Hard water contains soluble

Ca^{2+}

and

Mg^{2+}

ions. When soap (sodium/potassium salts of fatty acids, e.g.,

RCOONa

) is added, it forms insoluble calcium and magnesium carboxylates (

scum

), removing soap molecules from solution and hindering micelle formation. Thus, statement 2 is correct.

Precipitation of fatty acid salts depletes active surfactant molecules.

Analyze statement 3 regarding synthetic detergent structure and biodegradability

Detergents with highly branched alkyl chains cannot be degraded easily by sewage bacteria, leading to persistent foaming and water pollution. Linear alkylbenzene sulfonates (LAS) are straight-chain compounds easily broken down by microorganisms. Therefore, branched-chain detergents are less biodegradable than linear-chain detergents, making statement 3 incorrect.

Steric hindrance from alkyl branching prevents microbial enzymatic breakdown.

Key Concept

Chemical mechanisms of bleaching agents, soap-hard water interactions, and environmental biodegradability of surfactant hydrocarbon chain structures.

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