Question

When an aqueous solution suspected of containing Ba2+ or Pb2+ or both are mixed with sulfuric acid a precipitate forms. in another test, when the original solution is mixed with an aqueous solution of sodium sulfide no precipitate forms. What do these two tests indicate about the likel presence of Ba2+ and Pb2+ in the original solution? Explain your answer.

Answer 1

Ba ions, perhaps.
Pb ions, no.

Pb^+2 + H2SO4 ==> PbSO4(s) + 2H^+
Ba^+2 + H2SO4 ==> BaSO4(s) + 2H^+
Note: Both BaSO4 and PbSO4 are insoluble in water solution and both are white. This test indicates that either or both could be present (as well as other ions).

Ba^+2 + Na2S ==> no reaction since BaS is soluble in water.
Pb^+2 + Na2S ==> PbS(s) + 2Na^+
PbS is black and is insoluble in water solution.
Since there was no ppt with this reagent, Pb is definitely absent. Ba^+2 may still be present but there is no definite proof of that.