How will you distinguish NH₄OH solution from NaOH solution?

NH₄OH and NaOH can be distinguished by using CuSO₄.

CuSO₄ forms a pale blue precipitate which is insoluble in excess of sodium hydroxide and with ammonium hydroxide it forms a pale blue precipitate which dissolves in excess of ammonium hydroxide and forms a deep/inky blue solution.

$\underset{\text{blue}}{{\text{CuSO}$4}} + \underset{\text{caustic soda - colourless}}{2\text{NaOH}} \longrightarrow \underset{\text{pale blue ppt}}{\text{Cu(OH)}2} ↓ + \underset{\text{colourless}}{\text{Na}2\text{SO}4}

$\underset{\text{blue}}{{\text{CuSO}$4}} + 2\text{NH}4\text{OH} \longrightarrow \underset{\text{pale blue ppt}}{\text{Cu(OH)}2} ↓ + \underset{\text{colourless in solution}}{(\text{NH}4)2\text{SO}4}

$\text{Cu(OH)}$2 + (\text{NH}4)2\text{SO}4 + 2\text{NH}4\text{OH} \longrightarrow \underset{\underset{\text{copper (II) sulphate}}{\text{Tetraammine}}}{[(\text{Cu(NH}3)4]\text{SO}4} + 4\text{H}_2\text{O}