Question

An aqueous solution of a substance gives a white precipitate on treatment with dil. HCl which dissolves on heating. When H₂S is passed through the hot acidic solution, a black precipitate is obtained. The substance is a

a) Hg₂²⁺ salt 

(b) Cu²⁺ salt

(c) Ag⁺ salt 

(d) Pb²⁺ salt

Answer 1

Correct option is (d) Pb²⁺ salt

The given substance is a salt of lead (II). It reacts with dil. HCl to form white precipitate of lead chloride.

Pb²⁺ + 2HCl → PbCl₂ ↓ (black) + 2H⁺

Lead chloride has low solubility in cold water and it dissolves in hot water.

It reacts with sulphide ions from hydrogen sulphide to form a black precipitate of lead sulphide.

PbCl₂ + H₂S → PbS ↓ (black) + 2HCl