Question

How to distinguish ammonium hydroxide from sodium hydroxide?

Answer 1

Answer:

The initial reaction of both NH4OH and NaOH with CuSO4 is the same. The Cu 2+ ions react with the OH- ions from the NaOH or the NH4OH to produce insoluble Cu(OH)2

Cu2+(aq) + 2OH- (aq) → Cu(OH)2 (s)

The hydroxide is very finely suspended in the solution which has a light blue colour. This applies to both reactions.

Adding more NaOH to this solution , produces no change. There is no change in the color or appearance of the solution.

But if the solution containing the Cu(OH)2 produced by reacting the CuSO4 with NH4OH is treated with additional NH4OH a further reaction takes place. As more NH4OH is added the insoluble Cu(OH)2 will dissolve because soluble [Cu(NH3)4] 2+ ions are formed. The copper ammonia complex ion has a deep purple color , which makes the solution much darker - and there is no insoluble Cu(OH)2 remaining. You have have a solution of the copper - ammonia complex.

This is how you distinguish between solutions of sodium hydroxide and ammonium hydroxide using copper sulphate solution.