223 1.Chemical Reactions IlI ter addition of ammonium sulfate to an unknown solu

Question

223 1.Chemical Reactions IlI ter addition of ammonium sulfate to an unknown solution, no precipitate forms After addition of ammonium carbonate to the unknown solution, a white precipitate forms. Which possible metal ions are present? What further reaction or experiment could you perform to narrow down your choices, and what results would you expect ior each of your suspect metal ions? 7Af An unknown solution gives a brick-red flame test. The solution produced a white precipitate with ammonium carbonate, ammonium sulfate, and ammonium phosphate after heating. Silver nitrate is added to the solution to give a pale creamy colored precipitate. Dilute ammonia is added to that precipitate but the precipitate remains. After adding concentrated ammonia, the precipitate dissolves. What is the likely formula of the salt and why?

Explanation / Answer

1. Ammonium carbonate precipitates group 5 basic radicals like Ba2+ Ca2+ and Sr2+ ions.

since the solution doesn't give precipitation with ammonium sulphate solution the cation present is not Sr2+. Because Sr2+ give white precipitate with ammonium sulphate solution.

Hence the solution may contain Ca2+ or Ba2+ ions. For Ba2+ ion perform

potassium chromate test: given solution + acetic acid + potassium chromate, gives a bright yellow precipitation which means Ba2+ is present.

Flame test: if the solution gives apple green color to the flame its Ba2+

If Ca2+ is present perform

Ammonium oxalate test: given solution + acetic acid+ ammonium oxalate solution, give white precipitate which confirms the presence of calcium.

Flame test: if the solution gives brick red to the flame its Ca2+

2. Since the solution gives brick red to the flame the cation present is Ca2+. Since it gives precipitation with AgNO3 its a halide anion and according to the chart given the halogen is bromide Br- since the pale yellow precipitate dissolves in concentrated Ammonia solution. So the salt is calcium bromide CaBr2

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