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a solution may contain any of cation you tested for in group iii. addition of nh

ID: 1037599 • Letter: A

Question

a solution may contain any of cation you tested for in group iii. addition of nh3 and nh4cl a buffer 990 130 9. A solution may contain any of the cations you tested for in Group III. Addition of NH, and NH CI to the solution gives a reddish precipitate that turns black when HzS is added. The final precipitate is completely soluble in HCL Treatment of the HCl solution with NaOCI and NaOH produces a colorless solution and a precipitate that is completely soluble in H2S04. Given this information, state which lons must be present, absent, or are stili in doubt. Explain your answer. (use the flow chart to help youl) Present: Absent Still in Doubt:

Explanation / Answer

1)

Addition of NH3 and Nh4Cl gives a reddish precipitate that turns black when H2S is added.

The cation could be Ni2+, Co2+, Fe2+, Al3+, Zn2+

2)

Final precipitate is completely soluble in HCl

The cation could be Fe2+, Al3+, Zn2+ [Ni2+]

3)

Treatment with NaOCl and NaOH gives colorless solution with precipitate, completely soluble in H2SO4

The cation could be Fe2+, [Ni2+]

Present: Inconclusive

Absent: Co2+, Al3+, Zn2+

Still in doubt: Fe2+, Ni2+