Question

A solution which is 10⁻³ M each in Mn²⁺,
Fe²⁺, Zn²⁺ and Hg²⁺ is treated with 10⁻⁶ M
sulphide ion. If K????p of MnS, FeS, ZnS and
HgS are 10⁻¹⁵, 10⁻²³, 10⁻²⁰ and 10⁻⁵⁴–54
respectively which one will precipitate first
(a) FeS (b) MgS
(c) HgS (d) ZnS

Answer 1

(c) HgS

Explanation:

Given: K(sp) of MnS, FeS, ZnS and HgS are 10⁻¹⁵, 10⁻²³, 10⁻²⁰ and 10⁻⁵⁴ respectively.

Salt having low K(sp) will precipitate first. Among the given list, Mercury sulphide has the lowest K(sp). So HgS will precipitate first.

Option C is the answer.