Multiple choice 6- Upon the addition of 6M HCI to solution containing cations fr
ID: 558873 • Letter: M
Question
Multiple choice 6- Upon the addition of 6M HCI to solution containing cations from group I, Group II, and Group III a white precipitate forms, what cations could be present? (5 points) C- Fe, Ni2 You took the supernatant from the previous question and added 6M HCI to make the pH 0.5 and then added 10 drops of 1M thioacetamide and black brownish precipitate forms, what cations could be present? (5 points) 7- A- Ag, Pb2+ C- Fe2, Ni2 You took the supernatant from question 7 and added enough 6M NHs until the solution is alkaline to litmus paper. After it was alkaline to litmus paper you added IM thioacetamide, heated the solutio cations could be present? (5 points) A- Ag+, Pb2+ 8- on and centrifuged and a precipitate formed. What B- Cu2+, Cd2 C- Fe2+, Ni2Explanation / Answer
6) Group-I cations readily react with HCl and form insoluble precipitates. Here, Ag+ and Pb2+ will react with HCl and form AgCl and PbCl2 as precipitate.
7) Clearly, the supernatant will be free of Ag+ and Pb2+. Now, we know that thioacetamide is a very good in situ source of sulfides. It racts with the metal cations of group-II and group-III forming the corresponding insouluble sulfides in acidic media. Here, the insoluble products are CuS and Bi2S3
8) Till now, we have separated Ag+, Pb2+, Cu2+ and Bi3+ as precipitate. We can easily reject the options A and B which will result in option C as answer. Generally, sulfides of Fe2+ and Ni2+ are soluble in acidic solutions but at moderate pH (around pH 9), they form an insoluble sulfides and separates out from the solution as precipitate.
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