Question

How are Cu2+ and Zn2+ ions precipitated from the solution

Answer 1

Explanation:

This is because K

sp

of CuS is very low as compared to that of ZnS. Therefore, a low concentration of S

2−

ions can precipitate Cu

2+

ions as CuS, whereas, a high concentration of S

2−

ions is required to precipitate Zn

2+

ions as ZnS.

Now, in presence of an acid i.e., HCl dissociation of H

2

S is suppressed due to common ion effect.

HCl⇌H

+

+Cl

−

(strong electrolyte)

H

2

S⇌2H

+

+S

2−

(weak electrolyte)

As a result, in acidic solution copper will precipitate as CuS but not the Zinc as ZnS