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

ID: 512243 • Letter: A

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?

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 s 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? S Definitely absent Possibly present Ag 2+ Cd 2+ 2+. Fe The complete protocol and a list of possible 2+ precipitates can be found here Mn 2+ Cr K+ 4+ Sn 2+. Mg 3+. 2+. g2 2+ Hg 2+ Pb

Explanation / Answer

Group I cations precipitate with dilute HCl : Present

Group II cations precipitate with H2S in dilute HCl : Present

Group IV cations precipitate at higher pH with H2S : absent

Group V cations precipitate with Na2CO3 in basic medium : Present

Group VI cations does not precipitate with any reagent : May be present

Thus cations present here would be,

Definietly present

Ag+

Pb2+

Bi3+

Hg2^2+

Cd2+

Sn4+

Ca2+

Possibly present

Mg2+

K+

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