JAMB Chemistry 2019 Objective — Question 29

Question 29 of 40 from the Joint Admissions and Matriculation Board (JAMB) Chemistry 2019 Objective paper, with the correct answer and a full explanation.

The cation which forms a white precipitate soluble in excess of both sodium hydroxide and ammonia solution is

A. Pb²⁺
B. Zn²⁺Correct
C. Al³⁺
D. Ca²⁺

Explanation

With NaOH, Ca²⁺, Zn²⁺, Pb²⁺ and Al³⁺ all form white precipitates initially, but only Zn²⁺, Pb²⁺ and Al³⁺ dissolve in excess NaOH. With ammonia solution, only Zn²⁺ forms a precipitate that dissolves in excess reagent (as a soluble complex) — the others do not.

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