A solution may contain any of the Group II cations. Treatment of the solution wi

Question

A solution may contain any of the Group II cations. Treatment of the solution with thioacetamide in acid solution gives a black precipitate that is partially solution in strongly alkaline solution. The precipitate that remains is soluble in 6 M HNO3. The alkaline solution, when acidified produces an orange precipitate. The solution in HNO3 turns a deep blue upon the addition of 15 M NH3 and no precipitate is observed in this solution. On the basis of this information, which ions are present, which are absent, and which are still in doubt? Justify the choices made.

Explanation / Answer

As for the original precipitate being black, a IIA cation (Pb2+, Cu2+, Cd2+, Bi3+) must be present. The only IIB cation with a black sulfide is Hg2+ which we ruled out above. Of these four, when the acid extract is made alkaline with NH3, Cu2+ and Cd2+ will form soluble amine complexes, the deep blue color is indicative of the present to the deep blue complex ion, Cu(NH2) 2+, formed from the Cu2+. Additionally, the addition of chromate ion in the form of potassium chromate precipitates the lead ion as the orange yellow lead chromate which confirms the presence of lead ion.

Cd2+is absent and Bi3+ are still in doubt.

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.