A solution containing a mixture of metal cations was treated with dilute HCl and
ID: 853368 • Letter: A
Question
A solution containing a mixture of metal cations was treated with dilute HCl and no precipitate formed. Next, H2S was bubbled through the acidic solution. A precipitate formed and was filtered off. Then, the pH was raised to about 8 and H2S was again bubbled through the solution. A precipitate again formed and was filtered off. Finally, the solution was treated with a sodium carbonate solution, which resulted in no precipitation. Which metal ions were definately present, which were definitely absent, and which may or may not have been present in the orginal mixture?
(Definitely Present)-(Definitely Absent)-(Possibly Present)
Pb2+
Hg2+
Ca2+
Mn2+
Ni2+
Co2+
Sn2+
K+
Mg2+
Hg2+
Ag+
Bi3+
Cd2+
Explanation / Answer
Ag^+ and Hg2^2+ are definitely not present, since there is no precipitate upon addition of HCl.
Pb^2+, Sn^4+, Hg^2+, Cu^2+, and Sb^3+ might be present. Normally, Pb^2+ is precipitated upon addition of HCl, but this does not always happen; however, PbS would definitely precipitate. the other ions listed here would also precipitate in the presence of acidified H2S.
At least one of Mn^2+ and Ni^2+ were also present, but it is difficult to say which. These ions precipitate in basic solution upon addition of H2S.
Mg^2+ and Ba^2+ were not present, as they would have precipitated upon the addition of carbonate.
K^+ might be present, but it is impossible to say based on the information given
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