Reaction of transition metal ions with sodium hydroxide

If you add sodium hydroxide solution to most transition metal ions, you will get a coloured precipitate.

If the precipitate dissolves on addition of excess sodium hydroxide solution, then the transition metal ion is amphoteric.

An amphoteric species can react as both an acid and a base.

Here is a table of the reactions you need to know:

The ionic equation for the reaction of Cr³⁺ are:

Cr³⁺(aq) +3OH⁻(aq) → Cr(OH)₃​ (s)

Cr(OH)_3​(s) + 3OH⁻(aq)→ [Cr(OH)₆​]³⁻(aq)