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JAMB Chemistry 1995 Question 37

Question 37

Qualitative Analysis

Which of the following ions will give a white precipitate with aqueous NaOH and soluble in excess of the base?

  1. A.Ca2+
  2. B.Mg2+
  3. C.Zn2+
  4. D.Cu2+
Show the answer and explanation

Answer: C (Zn2+)

Explanation

Zn2+ forms white Zn(OH)2, which is amphoteric and dissolves in excess NaOH. Ca(OH)2 and Mg(OH)2 stay undissolved, and Cu(OH)2 is blue.