Question

A student analyzing an unknown solution containing some of thecations studied in this module records the following results. Ateach step, indicate which cations are present and which have beenproven absent from the unknown mixture.

1) 4 drops of 6M HCl solution are added to the unknown solution andno precipitate
2) The pH of the solution from (1) is raised to 9.5 by the additionof 6M NH3 solution. A cloudy, red-brown reaction mixtureresults
3) The solution from (2) is centrifuged, and the colorlesssupernatant liquid is decanted into a separate container for lateranalysis. The precipitate is rinsed, and 6M NaOH solution is added.The mixture is heated and then centrifuged, resulting in ared-brown precipitate and a clear, colorless supernatantliquid.
4) The precipitate from (3) is dissolved in 6M HCl solution, the pHis adjusted to 5, and 0.1M K4Fe(CN)6 solution is added to theprecipitate, resulting in the formation of a dark blue precipitatein a blue solution
5) When 6M HCl, aluminon, and 6M NH3 solutions are added to thesecond supernatant liquid from (3), a clear, red solutionresults.
6) When 0.5M (NH4)2C2O4 solution is added to the first supernatantliquid from(2), a clear, colorless solution results
7) The solution from (6) is heated to dryness with HNO3, and theresidue dissolved in 6M HCl solution. The solution remains clearand colorless following the adjustment of the pH of the solution to12 with the addition of 6M and 1M NaOH solution
8) When 6M CH3COOH followed by 0.1M Na3Co(NO2)6 solutions are addedto the solution from (7), a yellow precipitate forms.