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JEE Main levelSingle correct optionDifficulty 2 of 3el173

Sodium stearate solution is added to a sample of hard water containing $Ca X^{2 +}$ ions. The white scum that appears is

Asodium chloride, $NaCl$
Bcalcium carbonate, $CaCO X_{3}$
Ccalcium stearate, $(C X_{17} H X_{35} COO) X_{2} Ca$
Dstearic acid, $C X_{17} H X_{35} COOH$

Answer: C

Stearate anions exchange sodium for calcium:

2 C X_{17} H X_{35} COO X^{-} + Ca X^{2 +} (C X_{17} H X_{35} COO) X_{2} Ca ↓

. Calcium stearate is insoluble and separates as scum, wasting soap. The solution is not acidic, so free stearic acid is not formed.

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