What would be observed when aqueous ammonia is added in drops and then in excess to a solution of copper(II) ions?
-
blue precipitate is formed which is soluble in excess ammonia
- brick red precipitate is produced which is insoluble in excess ammonia
- white precipitate is formed which is excess in ammonia
- green precipitate is formed which is insoluble in excess ammonia
The correct answer is: A
Explanation
When a few drops of ammonia solution is added to copper(II) ions, a blue precipitate of copper(II) hydroxide is formed.
CuSO₄(aq) + 2NH₃(aq) + 2H₂O(ℓ) ⇌ Cu(OH)₂(s) + (NH₄)₂SO₄(aq)
However, when ammonia solution is added in excess, the blue precipitate re-dissolves to form a deep blue solution of tetraamine copper(II) hydroxide.
Cu(OH)₂(s) + 4NH₃(aq) → [Cu(NH₃)₄](OH)₂(aq). Therefore, the correct answer is option A.