Question

You are presented with a white solid and told that due to careless labeling it is not clear if the substance is silver fluoride, calcium fluoride, or potassium bromide. When you transfer the solid to a beaker and add water, the solid dissolves to give a clear solution. Next a Na2SO4(aq) solution is added and a white precipitate forms. What is the identity of the unknown white solid?

Answer 1

Because the solid is soluble in water, it cannot be calcium fluoride.
This leaves us with either silver fluoride or potassium bromide, as both are soluble in water.

Upon addition of sodium sulfate, a white precipitate forms, confirming that the substance was silver fluoride as the precipitate are of silver sulfate.