Question

For the following Assertion and Reason, the correct option is:

Assertion (A): When Cu (II) and sulphide ions are mixed they react together extremely quickly to give a solid.

Reason (R): The equilibrium constant of \[\ce{Cu^{2+}(aq) + S^{2-}(aq) <=> CuS(s)}\] is high because the solubility product is low.

Options

• (A) is false and (R) is true.

• Both (A) and (R) are false.

• Both (A) and (R) are true but (R) is not the explanation for (A).

• Both (A) and (R) are true and (R) is the explanation for (A).

Answer 1

Both (A) and (R) are true but (R) is not the explanation for (A).

Explanation:

\[\ce{CuS <=> Cu^{2+} + S^{2-}}\]

∴ k_sp = [Cu²⁺] [S²⁻]

k = `(["CuS"])/(["Cu"^(2+)]["S"^(2-)])`

In the presence of acidic medium, when H₂S is passed through the solution. H₂S being a weak acid produces a low concentration of S²⁻ ions in the solution corresponding to the solvability product of CuS. As the solubility product of Cus n very low (3 × 10⁻² at 25°C) i.e why Cu²⁺ and S² ions react extremely quickly to give a solid of CuS. Again equilibrium constant is related with solubility product in but it is not the correct explanation for [A].