when an aqueous solution suspected of containing BA2+ or Pb2+ or both is 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 likely presence of Ba2+ and Pb2+ in the original solution? Explain your answer.
Pb is present. Ba is not present. Do you know why?
Ba^+2 + SO4^= ==> BaSO4(s) white ppt.
Pb^+2 + SO4^= ==> PbSO4(s) white ppt.
Ba^+2 + S^= ==> BaS is soluble; therefore, no ppt.
Pb^+2 + S^= ==> PbS(s) black ppt.
The first test involving the addition of sulfuric acid to the aqueous solution can help identify the presence of Ba2+ and/or Pb2+ ions in the original solution. When sulfuric acid is added to an aqueous solution containing Ba2+ or Pb2+ ions, a precipitate forms. This precipitate is insoluble and appears as a white solid.
To verify the presence of Ba2+ and/or Pb2+ ions, you can perform the following steps:
1. Take a sample of the aqueous solution suspected to contain Ba2+ and/or Pb2+ ions.
2. Add a few drops of sulfuric acid to the solution.
3. Observe any formation of a white precipitate.
If a white precipitate forms upon the addition of sulfuric acid, it indicates the likely presence of either Ba2+ or Pb2+ ions, or both, in the original solution. The sulfuric acid reacts with these metal ions to form insoluble sulfates:
Ba2+ (aq) + SO4^2- (aq) → BaSO4 (s)
Pb2+ (aq) + SO4^2- (aq) → PbSO4 (s)
However, if no precipitate forms in the first test, it indicates the absence or a lower concentration of Ba2+ and Pb2+ ions in the original solution.
The second test involving the addition of an aqueous solution of sodium sulfide to the original solution can provide further confirmation. Ba2+ and Pb2+ ions react with sulfide ions (S^2-) to form insoluble sulfides:
Ba2+ (aq) + S^2- (aq) → BaS (s)
Pb2+ (aq) + S^2- (aq) → PbS (s)
If no precipitate forms upon the addition of sodium sulfide, it suggests that neither Ba2+ nor Pb2+ ions are present in the original solution.
In summary, if a precipitate forms when sulfuric acid is added, indicating the presence of Ba2+ and/or Pb2+ ions, it implies their likely presence in the original solution. Conversely, if no precipitate forms when sodium sulfide is added, it suggests the absence of Ba2+ and Pb2+ ions in the original solution.