Question

A sample consists of one or more of the following salts: Cu(CH₃CO₂)₂ (acetate), BaCl₂, (NH₄)₂SO₄, SrCO₃, KNO₃. The sample, when treated with water, gives a white precipitate that is filtered off and a blue solution. The precipitate is a white solid that is completely insoluble, both in water and in 6M HCl solution.

Which compounds MUST be present? Explain why. (Write the formulae and present your evidence).

Which compounds MUST be absent? Explain why. (Write the formulae and present your evidence).

Which compounds are INDETERMINATE - unable to determine if present or absent. (Write the formulae).

Answer 1

blue solution --> Cu2+ ions present for sure

white precipitate could be:

BaCO3, BaSO4, ;note that BaCO3 is not likely to occur, since Cu2+ + CO3-2 should also form blue CuCO3(s) precipitate

if not soluble in 6M HCl , then... most likely not CO3-2

thereofre, BaSO4 is most likely present, for sure

Which compounds MUST be present? Explain why. (Write the formulae and present your evidence).

for sure, Cu2+ ions,

Ba2+ due to white precipitate with sO4-2 and (NH42)SO4 also present

so..

Cu(CH3CO2)2 (acetate), BaCl2, (NH4)2SO4 most likely present

Which compounds MUST be absent? Explain why. (Write the formulae and present your evidence).

as stated, CO3- could not be present, so SrCO3 is not present

Which compounds are INDETERMINATE - unable to determine if present or absent. (Write the formulae).

KNO3, since it will not form any kind of precipitate