Unknown solution containing Group A cations (Fe3+, Mn2+, Bi3+) and Group B catio

Question

Unknown solution containing Group A cations (Fe3+, Mn2+, Bi3+) and Group B cations (Al3+, Cr3+, Sn4+) is treated with the steps below. In each each stage, explain how each step can indicate which cations may be present, which are defintely present, or which are absent.

1. Solution is treated with NH3 until the pH is 9, producing a colored precipitate. The precipitate is treated with sodium hydroxide and hydrogen peroxide, centrifuged and separated to give a yellow solution and a precipitate. The yellow solution is saved for group B cation analysis. The remaining precipitate was dissolved in HCL and the clear solution is analyzed.

All group A cations may be present?

2. A few drops of the clear solution from step a are treated with NaBaiO3, to give a purple solution.

Mn2+ definitely present?

3. Two drops of solution from step 1 are treated with NaOH and solid SnCl3 to give a black solid

Not sure about this one. Bi3+ might be present or confirmed present?

4. A portion of the solution from step a is treated w/ KSCN and the solution is clear

None present?

Explanation / Answer

Qualittive analysis of metal cations

1. The yellow solution confirms presence of Cr3+ (yellow colored CrO4^2-) and absence of Al3+ or Sn4+ cation which are both colorless.

2. Mn2+ reacts with BiO3- ion to form a purple coloration to the solution. this confirms presence of Mn2+ cation.

3. Formation of black solid confirms reduction of Bi3+ to Bi(0). this confirms presence of Bi3+ cation.

4. Clear solution with KSCN confirms absence of Fe3+ in solution.

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