Question

Assertion: Soft water lathers with soap but not hard water.
Reason : Hard water reacts with soap to form insoluble salts which form scum, not lather.

• A. If both assertion and reason are true and reason is the correct explanation of assertion.
• B. If both assertion and reason are true but reason is not the correct explanation of assertion.
• C. If assertion is true but reason is false.
• D. If both assertion and reason are false.

Answer 1

Answer: (A)

Hard water contains calcium and magnesium salts which react with soap containing sodium stearate $\left( C _{17} H _{35} COONa \right)$ to precipitate out $Ca / Mg$ stearate.
$2 RCOONa + Ca ^{2+} \rightarrow( RCOO )_{2} Ca +2 Na ^{+}$
$2 RCOONa + Mg ^{2+} \rightarrow( RCOO )_{2} Mg +2 Na ^{+}$