Question

State True or False.

The white precipitate formed on treating with NaOH confirms the presence of zinc cations in a solution.

• A. True
• B. False

Answer 1

The correct option is B False

The given statement is False.
The white precipitate formed on treating with hydrogen sulphide in ammoniacal solution confirms the presence of zinc cations in a solution. Zinc sulphide (white ppt) is insoluble in ammonium hydroxide solution.
$Z{n}^{2+}+H_{2}S\stackrel{N{H}_{4}OH}{\to }ZnS+2H^{+}$
Note: $Z{n}^{2+}$ ions combine with NaOH to form precipitate of $Zn(OH{)}_2$ which is soluble in excess NaOH.
$Z{n}^{2+}+2NaOH\to Zn(OH{)}_2\downarrow +2NaCl$
$Zn(OH{)}_2+2NaOH\to N{a}_{2}Zn{O}_2+2H_{2}O$