The unknown solution below may contain the following ions: Ag^+, Pb^2+, Al^3+, F
ID: 526727 • Letter: T
Question
The unknown solution below may contain the following ions: Ag^+, Pb^2+, Al^3+, Fe^3+, Mn^2+, Mg^2+, Co^2+, Cu^2+, Ni^2+, NH_4^+. Upon addition of 6 M HCl, a while precipitate formed (solid A). The solution. which contained the group II ions, was separated from solid A. The solution II. which contains the group II ions was decanted from a while precipitate. This white solid did not dissolve in the hot water bath but the solid did dissolve in aqueous ammonia. The same white precipitate was formed after adding nitric acid. The addition of ammonium carbonate to the decanted solution did not result in a precipitate despite the solution being basic. The group II ion solution (solution II) was made slightly basic to yield a precipitate (solid C). After decanting solid C from solution III, 6 M NaOH was added to solid C until strongly basic in which some of solid C dissolved. The resulting solution was then decanted from solid C. Phosphoric acid was added to this solution that produced a white precipitate. Solid C dissolved upon treatment with nitric acid to form solution D that was then divided between two test tubes. Solution D turned a reddish-purple in the presence of NaBiO_3 but there was no visible reaction in the presence of KSCN. Treatment of solution III with a 1 M Na_2 HPO_4 solution yielded a white precipitate that was decanted from solution III. After heating to dryness, the resulting residue was acidified and then the solution was partitioned between four small test tubes. To the first test tube, a spatula tip of KI was added to produce a tan solid/brown liquid. In the second test tube, no change was visible with the addition of a few drops of the DMG solution. To the third test tube. 1 mL of the NN solution was added to the solution that resulted in the formation of a red-brown precipitate. The contents of the fourth test tube were added to a hot NaOH solution that gave a positive test for the ammonium ion. Present: ____ A possible false positive: ___Explanation / Answer
Group I cation form precipitate with 6 M HCl, so Ag+ or Pb2+ may be present
The solid A did not dissolve in hot water, so Ag+ is present which dissolved in NH3 and reprecipitated with HNO3
No precipitate upon addition of (NH4)2CO3 in basic solution, Mg2+ absent
Group II cations, forms solid C with basification, Bi3+ present
No precipitate with KSCN, Fe3+ absent
Precipitate with NaBiO3, Mn2+ present
No change by adding DMG, Ni2+ absent
Precipitate with KI, Cu2+ present
Present : Ag+, Mn2+, Cu2+, NH4+
A possible false positive : Al3+, Co2+
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