2. Consider the following analysis. (Remember: A conclusion must state what ion
ID: 567711 • Letter: 2
Question
2. Consider the following analysis. (Remember: A conclusion must state what ion is/may be absent or present as well as what any ppt may be and what significant species may be in solution.) sie received her Group il unknown solution. Her first observation was that it was colorless. Su Her conclusion?abrel rom joun bl She a took about half of her sample, adjusted the pH so that it was not lower than 0.5, added thioacetamide, and warmed the solution. A dark precipitate (1) formed. o Her condlusion? CA 14 Following the regular procedure, she treated ppt (1) with potassium hydroxide and stirred. She not tell for sure if any of the ppt dissolved. could Her conclusion? She centrifuged, and decanted the supernatant solution (2) into a clean tt. She treated the remaining ppt (3) with 3M HCI solution. Some very black ppt (4) remained and she decanted the solution (5) into a clean tt. Her conclusion? She made solution (5) basic with ammonia, added thioacetamide and warmed it. A yellow ppt formed. Her conclusion? She forgot to check out solution (2) and cleaned up all her glassware. In summary, which cations are present absent in doubtExplanation / Answer
Qualitative analysis of Group II cations
Adding thioacetamide forms dark color precipitate
Hg2+, Cu2+, Bi3+, Pb2+ may be present
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Added KOH, could not tell If precpitate dissolved
Hg2+, Cu2+, Bi3+, Pb2+ may be present
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centrifuged and decanted filtrate. Precipitate treated with HCl. Black ppt remained,
Hg2+ present
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Made solution basic, added thioacetamide and warmed. A yellow ppt formed.
Cd2+ present
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In summary,
cations present : Hg2+, Cd2+
Cations absent : Cu2+
in doubt : Pb2+, Bi3+
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