Question

Why h2s is added in hcl for precipitation of second group radicals

Answer 1

Answer:

Explanation:

The second group cations are separated in the form of their sulphides.

However their solubility product is less than the fourth group cations that are also separated as sulphides.

So we need a limited amount of sulphide ions. The concentration of sulphide ions is suppressed by HCl due to common ion effect.

The already present H+ ions suppress the dissociation of H2S by moving the reaction in the backward reaction.

HCl → H+ + Cl-

H2S ⇋​ 2H+ + S2-

Hence a lesser no of sulphide ions is produced so that only those cations are precipitated having lower solubility product.