What happens when zinc sulfate is treated with excess of caustic potash solution ?
Sodium hydroxide reacts with metallic salts to form hydroxides which may be insoluble or dissolve in excess of NaOH to form salts of oxyacids. Some of the hydroxides decompose into insoluble oxides,
Zinc salt forms insoluble hydroxide with NaOH, which dissolves in excess of NaOH.
ZnSO4+2NaOHZn(OH)2+Na2SO4 white (insoluble)
Zn(OH)2+2NaOHNa2ZnO2+2H2O sodium zincate (soluble)