Question

observation when sodium hydroxide is added to a solution containg copper ions​

Answer 1

Answer:

If copper exists in the form of salt, and it is called precipitation reaction. Cu2+(aq)+2NaOH(aq)→ Cu(OH)2(s)+2Na+(aq), which gives a very beautiful blue precipitate. ... Some basic salts may also form. The precipitate does not dissolve in excess sodium hydroxide unless theNaOH solution is very concentrated.

Explanation:

Hydroxide ions (from, say, sodium hydroxide solution) remove hydrogen ions from the water ligands attached to the copper ion. Once a hydrogen ion has been removed from two of the water molecules, you are left with a complex with no charge - a neutral complex. This is insoluble in water and a precipitate is formed.