A solution containing a mixture of metal cations was treated as follows 1. Dilut

Question

A solution containing a mixture of metal cations was treated as follows 1. Dilute HCl was added and no precipitate formed 2. H2S was bubbled through the acidic solution. A precipitate formed and was filtered off 3. The pH was raised to about 9 and H2S 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? Cation Group Ag+, Pb2+, Hg22+ Bi3+, Cd2+, Cu2+, Hg2+ | form acid-insoluble Pb2, Sb3*, Sn2* Sn4* sulfides A3+ Co2+, Cr3+ Fe2+ form base-insoluble Fe3*, Ni?-, Mn2* Zn2* Sulfides or hydroxides Description form insoluble chlorides Present in the original solution? At least one of these ions was present At least one of these ions was present. None of these ions were present None of these ions were present. unknown +form insoluble carbonates Li, Na, K, NH4 completely soluble unknown All of these ions were present At least one of these ions was present None of these ions were present. There is additional feedback available! w this feedback by clicking on the tom divider bar. Click on the divider r again to hide the additional feedback Clnse Incorrect

Explanation / Answer

Step 1. Dilute HCl was added and no precipitate formed.

           From this step we can rule out the presence of Ag+, Pb2+ and Hg22+ because if any of these ions were present they would definitely form insoluble compound with chloride ions present in solution due to dissociation of HCl into H+ and Cl- ions. so none of these ions were present.

Step 2. H2S was bubbled through the acidic solution. A precipitate formed and was filtered off.

            From this step we can safely say that atleast one of the metallic cations from Bi3+, Cd2+, Cu2+, Hg2+, Pb2+, Sb3+, Sn2+, Sn4+, was present in the solution because a precipitate was formed indicating the reaction between atleast one of these cations and H2S which dissociates as 2H+ and S2-. so atleast one of these ions was present.

Step 3. The pH was raised to about 9 and H2S was again bubbled through the solution. A precipitate formed and was filtered off.

           From this step we can safely say that atleast one of the metallic cations fromAl3+, Co2+, Cr3+, Fe2+, Fe3+, Ni2+, Mn2+, Zn2+ was present in the basic solution because a precipitate was formed indicating the reaction between atleast one of these cations and H2S which dissociates as 2H+ and S2-. so atleast one of these ions was present.

Step 4. Sodium Carbonate was added to the filtered solution. A precipitate formed and was filtered off.

            From this step we can safely say that atleast one of the metallic cations from Ba2+, Ca2+, Mg2+, Sr2+ was present in the solution because these cations react with carbonate ions to form insoluble compounds which was obtained during this step. Sodium Carbonate (Na2CO3) dissociates as 2Na+ and CO32- ions in the solution. Hence At least one of these ions was present.

For the last group of metallic cations i.e., Li+, Na+, K+, NH4+ nothing can be said based on above 4 steps as these cations are completely insoluble and did not react with any of the added reactants. Hence their presence is unknown.

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