Alex was given a solution of an unknown salt Y for analysis. He performed the following tests and recorded his observations:
- To a part of the solution Y, he added silver nitrate solution and obtained a white precipitate which was soluble in ammonium hydroxide solution.
- To the remaining solution he added a few drops of sodium hydroxide solution and obtained a pale blue precipitate.
Based on the observations made by Alex, identify:
(a) the anion and
(b) the cation present in salt Y.
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(a) Anion — Chloride (Cl-)
(b) Cation — Copper(II) (Cu2+)
Reason —
(a) The white precipitate formed with silver nitrate solution which is soluble in ammonium hydroxide is silver chloride (AgCl). This indicates the presence of chloride ion (Cl-) as the anion.
AgNO3 + Cl- ⟶ AgCl ↓ [white ppt.] + NO3-
AgCl + 2NH4OH ⟶ [Ag(NH3)2]Cl + 2H2O
(b) The pale blue precipitate formed with sodium hydroxide solution is copper(II) hydroxide [Cu(OH)2]. This indicates the presence of copper(II) ion (Cu2+) as the cation.
Cu2+ + 2NaOH ⟶ Cu(OH)2 ↓ [pale blue ppt.] + 2Na+
Hence, the salt Y is copper(II) chloride (CuCl2).