Question

What is solubility product? Establish the relation between solubility and solubility product for CdS type compounds. In third group analysis, NH₄Cl is added before NH₄OH, Why?

Answer 1

Solubility Product: It is defined as the product of the concentration of ions in a saturated solution of an electrolyte at a given temperature. It is repersented by the symbol K_sp.

Relation between solubility and solubility product for CdS type compounds
Let x be the solubility of CdS

In third group analysis, NH₄ Cl is added before NH₄ OH because NH⁺₄ ions furnished by NH₄Cl lower the ionization of NH₄ OH and hence the concentration of OH^– ion. At low concentration of OH^– ion, III group hydroxides precipitate.

Whereas, when NH₄OH is added in the presence of NH₄Cl, the precipitation of group hydroxides takes place.