Question

What happens when sodium hydroxide is added in excess to zinc sulphate solution?

Answer 1

When sodium hydroxide is added to zinc sulphate solution:

1. Initially, a white precipitate of zinc hydroxide is formed.

\[\ce{ZnSO4 ​+ 2NaOH -> Zn(OH)2​↓ + Na2​SO4​}\]

2. In excess NaOH, the white precipitate dissolves to form a soluble sodium zincate solution.

\[\ce{Zn(OH)2​ + 2NaOH -> Na2​[Zn(OH)4​]}\]

Thus, zinc hydroxide is amphoteric and dissolves in excess sodium hydroxide.