Question

Distinguish between the following metal salt solutions.

Zinc and lead salts

Answer 1

Add ammonium hydroxide solution dropwise and then in excess to both the salt solutions.

Zinc salt:

Forms a white gelatinous precipitate of zinc hydroxide which dissolves in excess to form a clear, colourless solution.

\[\ce{ZnSO4 + 2NH4OH -> (NH4)2SO4 + \underset{(White gelatinous ppt.)}{Zn(OH)2↓}}\]

\[\ce{Zn(OH)2 + 4NH4OH -> \underset{(Clear, colourless solution)}{[Zn(NH3)4](OH)2} + 4H2O}\]

Lead salt:

Forms a chalky white precipitate of lead hydroxide which remains insoluble in excess.

\[\ce{Pb(NO3)2 + 2NH4OH -> 2NH4NO3 + \underset{(Chalky white ppt.)}{Pb(OH)2↓}}\]