What reagent would distinguish between Ba2+ and Pb2+? A) KCl B) Li2S2O3 C) K2SO4 D) LiNO3
The Correct Answer and Explanation is:
The correct reagent to distinguish between Ba²⁺ and Pb²⁺ is C) K₂SO₄.
Explanation:
Both Ba²⁺ (barium ion) and Pb²⁺ (lead ion) are common cations found in aqueous solutions, and distinguishing between them is important in various analytical chemistry applications. The key to distinguishing between these two ions lies in their different solubilities in certain salts, particularly sulfate salts.
- Barium Ion (Ba²⁺):
- When K₂SO₄ (potassium sulfate) is added to a solution containing Ba²⁺ ions, barium sulfate (BaSO₄) forms as a white precipitate. This is because barium sulfate has an extremely low solubility in water (it is nearly insoluble).
- The precipitation of BaSO₄ is a distinctive reaction that allows you to identify the presence of Ba²⁺.
- Lead Ion (Pb²⁺):
- Lead(II) sulfate (PbSO₄) also forms when K₂SO₄ is added to a solution containing Pb²⁺. However, PbSO₄ is only sparingly soluble in water, meaning that the precipitate might not form as readily or might appear much less than that of BaSO₄. The solubility product (Ksp) of PbSO₄ is higher than that of BaSO₄, so under certain conditions (such as lower concentrations), Pb²⁺ may stay in solution, though it would still precipitate to some extent.
Therefore, while both ions react with K₂SO₄ to form a sulfate precipitate, the key difference is that Ba²⁺ will always form a precipitate of BaSO₄, while Pb²⁺ might not form a precipitate as readily or will form a much less dense precipitate due to its higher solubility.
The other reagents (A) KCl, (B) Li₂S₂O₃, and (D) LiNO₃ do not effectively distinguish between Ba²⁺ and Pb²⁺ in a straightforward way through precipitation reactions.
