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JAMB Chemistry 1984 Question 48

Question 48

Qualitative Analysis

An aqueous solution of a metal salt, M, gives a white precipitate with NaOH which dissolves in excess NaOH. With aqueous ammonia, the solution of M also gives a white precipitate which dissolves in excess ammonia. Therefore the cation in M is

  1. A.Zn2+
  2. B.Ca2+
  3. C.Al3+
  4. D.Pb2+
  5. E.Cu2+
Show the answer and explanation

Answer: A (Zn2+)

Explanation

Zn(OH)2 is white and dissolves in excess of both NaOH and ammonia. Al(OH)3 and Pb(OH)2 do not dissolve in excess ammonia, and copper gives a blue precipitate.