sapling leaming A solution containing a mixture of metal cations was treated wit

Question

sapling leaming A solution containing a mixture of metal cations was treated with dilute HCI 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? Definitely present Definitely absent Possibly present

Explanation / Answer

From the chart given at the end of the page we have to identify the species which are definitely present.

Group III (Al3+, Cr3+, Fe3+, Zn2+, Ni2+, Co2+, Mn2+) cations produce slightly soluble sulfides (Ksp values more than 10-20) so they can be precipitated by relatively high amounts of sulfide ion; this can be achieved by adding a basic solution of H2S.

Thus, we can say that of all the species,

Fe2+, Cr3+, Mn2+ are definitely absent in the solution

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