Model Paper 3 — Question 21

(a) Add copper sulphate solution (CuSO₄) to both the solutions. With sodium hydroxide, a pale blue precipitate is formed which is insoluble in excess of sodium hydroxide. With ammonium hydroxide it forms a pale blue precipitate which dissolves in excess of ammonium hydroxide and forms a deep/inky blue solution.

(b) When ammonium hydroxide (NH₄OH) is added dropwise to Zinc chloride (ZnCl₂), white gelatinous precipitate of zinc hydroxide forms initially. On adding excess NH₄OH, the precipitate dissolves, forming a clear solution.

With calcium chloride, no precipitate forms with NH₄OH because calcium hydroxide is not precipitated by ammonium hydroxide in cold solution.