My answer was wrong. What is the correct answer ? A solution containing a mixtur

Question

My answer was wrong. What is the correct answer ? A solution containing a mixture of metal cations was treated as follows. 1. Dilute HCI was added and no precipitate formed. 2. H_2S was bubbled through the acidic solution. A precipitate formed and was filtered off. 3. The pH was raised to about 9 and H_2S was again bubbled through the solution. A precipitate formed and was filtered off. 4. Finally, sodium carbonate was added to the filtered solution. A precipitate formed and was filtered off. What can be said about the presence of each of these groups of cations in the original solution?

Explanation / Answer

Group 1 --> precipitates in acidic media with Cl-

Group 2 --> precipitates in acidic media with S-2

Group 3 --> precipitates in basic media with S-2

Group 4 --> precipitates in basic media with OH-

Group 5 --> does not preicpitate, we require flame test

knowing this

Group 1 = Ag+, Pb2+, Hg2+2

Group 2 = Hg2+, Bi3+ , Cu2+ , Cd2

Group 3 = Co2+, Ni2+, Fe3+, Mn2+, Cr3+, Al3+, Zn2+

Note that from

Step 1) no precipitate forms, so no Ag+, No Pb2+, No Hg2+2; therefore none of these ions are present

Step 2) precipaiteion implies --> there is at least 1 ion present

Step 3) increase of pH ---> at least 1 is present, since precipitate is formed

Step 4) If there is precipitate, then there is at least 1 ion present

Finally, no flame test was performed, so we can't know if Li+, Na+, K+, NH4+ was present so it is unkown

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