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 a precipitate formed. The solution was filtered and H2S was bubbled through the acidic solution. A precipitate again formed and was filtered off. Then, the pH was raised to about 8 and H2S was again bubbled through the solution. This time, no precipitate formed. Finally, the solution was treated with a sodium carbonate solution, which resulted in formation of a precipitate. Which metal ions were definitely present, which were definitely absent, and which may or may not have been present in the original mixture?

Co2+,Sn4+,K+,Mg2+,Hg2(2+),Ag+, Bi3+,Pb2+,Zn2+,Cd2+,Ni2+,Hg2+,Ca+

I understand that none are definitely present, but I need to know which ones are maybe present and definitely not present. I have seen the picture to accompany this question, and I do not understand it.

Explanation / Answer

Since the solution is giving ppt on adding dil HCl, therefore,Hg22+, Ag+and Pb2+ (group I cations) may be present.

On bubbling this acidic solution with H2S gas, ppt is again formed that means group II cations i.e; Sn4+,Hg2+,Bi3+and Cd2+ may be present.

Since the ppt is not being formed on raising the pH and passing the H2S gas again, thereforeGroup III and IV cations(Co2+,Zn2+,Ni2+)are absent.

On treating the solution with carbonate solution, ppt is formed which means that group V cation (Ca2+) is present.

One thing is to make sure that all cations of previous groups have been separated since they can also form their carbonate ppt.

K+ and Mg2+ group VI cations, so they may or may not be present.

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