For a solution containing at least one of the cations involved in this experimen

Question

For a solution containing at least one of the cations involved in this experiment, answer the following questions. (1) When 6M HCI is added to the solution, a white precipitate forms. What cation(s) may be present in the solution? (2) when hot water is added to the precipitate, a while solid remains after filtration. What cation(s) May be present? (3) When the filtrate from (2) is cooled, a white precipitate forms. What cation(s) may be present? (4) when the precipitate remaining in (2) after filtration is treated with aqueous NH_3 the precipitate completely dissolves, What conclusions cna be drawn about the presence or absence of the cation(s) in the solution? (5) If HNO_3 is added to the solution in (4), what would you expect to happen? Briefly explain.

Explanation / Answer

1. Cations present in the solution are Ag+, Pb2+ and Hg22+.

2. PbCl2 is fairly soluble in boiling water. Hg2Cl2 and AgCl, are not affected that much by hot water. The PbCl2 solid would dissolve in the hot water leaving one of the other chlorides.

3. The white solid is PbCl2 which is soluble when filtered but reprecipitates when cooled down.

4. The treatment of the precipitate from (2) with ammonia identifies the precipitate as AgCl.

AgCl(s) + 2 NH3(aq) --> [Ag(NH3)2]Cl This is soluble in ammonia solution.

5. If HNO3 is added the NH3 will react with HNO3 to produce NH4NO3(aq). The H+ ions added will compete for the presence of the NH3 much better than the AgCl. The AgCl will appear again as a precipitate.

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