An unknown solution may contain any of the seven cations listed below. One stude

Question

An unknown solution may contain any of the seven cations listed below. One student preformed a series of experiments to determine what ions are in the solution. Based upon the experiments performed by the students, the results are as follows: a) On addition of 6 M HCl, a white precipitate results. The white precipitate is then mixed with NH3 where it dissolves. b) When acidic H2S is added to the unknown, a black precipitate results, and is dissolved in NH3 giving a deep blue color. c) When ammonium carbonate, concentrated ammonia, and ammonium chloride are added to the unknown, a clear solution results. Classify the following ions as present, absent, or undetermined. (input the whole word)

Explanation / Answer

Unknown solution when treated with,

a) 6 M HCl, white ppt is formed. Group I metal cations form precipitate with HCl. So possible cation could be Ag+, Hg+, Tl+.

b) precipitate dissolved upon addition of NH3. Ag+ forms Ag(NH3)2^+ is soluble.

c) Acidic H2S is added forms black precipitate. Group II metal cations forms precipitate with acidic H2S. the cations could be thus, Hg2+, Pb2+, Br3+, or Cu2+.

d) The precipitate formed in c) dissolved upon addition of NH3 and forms a deep blue color. Cu2+ forms a deep blue color solution with NH3 as [Cu(NH3)4]2+ which is soluble.

e) A clear solution is obtained when (NH4)2CO3 , conc. NH3 and NH4Cl are added. The cations present could be NH4+, Mg2+ or Li+

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