A solution may contain Ag + , Pb 2+ , and/or Hg 2 2+ . A white precipitate forms

Question

A solution may contain Ag+, Pb2+, and/or Hg22+. A white precipitate forms when 6 M HCl is added. The precipitate is partially soluble in hot water. The supernatant and the precipitate are placed into two separate test tubes. The solid remaining after treatment with hot water turns black on addition of 6 M NH3. The supernatant is tested with K2CrO4 and a yellow precipitate forms. No other precipitates are observed while performing the procedure. Which of the ions are present and which are absent? State your reasoning with equations

Explanation / Answer

Solution :-

After adding the HCl white ppt is formed which is partially soluble means it’s the precipitate of the PbCl2 which when reacted with K2CrO4 gives the yellow color and confirms presence of the Pb^2+

Ag^+ do not form precipitate with the ammonia

But Hg2^2+ forms the precipitate with black color

This means Ag^+ is not present in the solution means Ag^+ is absent

Therefore only Pb^2+ and Hg2^2+ is present in the solution

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