A solution containing a mixture of metal cations was treated with dilute HCl and

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?

Explanation / Answer

Group I cations, Ag+, Pb+2, Hg2+2, should precipitate when HCl is added; since no precipitte forms, those ions are NOT present

Group II ions --> precipitate as S-2 when H2S is added (Hg2+, Bi3+ , Cu2+ , Cd2+)

Group III ions --> precipitate with H2S in basic conditions --> (Co2+, Ni2+, Fe3+, Mn2+, Cr3+, Al3+, Zn2+)

Group IV ions will precipitate with carbonates --> (Ca2+, Ba2+, Mg2+)

Group V ions --< K+, Na+; Require flame test

Then...

For sure they are NOT present:Ag+, Pb+2, Hg2+2; Ca2+, Ba2+, Mg2+

Possibly present:; Co2+, Ni2+, Fe3+, Mn2+, Cr3+, Al3+, Zn2+ ; K+, Na+

Definitevily present --> you can't be sure, unless specific test is used

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