Why does pure NaCl crystallise out when HCl gas is passed into a saturated solution of crude common salt?
Correct answer C. The common Cl⁻ ion lowers the solubility of NaCl
Explanation
Added HCl increases the Cl⁻ concentration, so the ionic product [Na⁺][Cl⁻] exceeds Ksp and pure NaCl precipitates. This is the common ion effect.
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