What reagent would distinguish between Ba2+ and Pb2+? A) KCl B) Li2S2O3 C) K2SO4 D) LiNO3
The Correct Answer and Explanation is:
The correct answer is C) K2SO4 (Potassium sulfate).
Explanation:
Ba²⁺ and Pb²⁺ are both divalent cations, and they belong to the same group in the periodic table, but they exhibit different solubility properties when reacting with certain anions. The key reagent here, K2SO4, plays an important role in distinguishing between these two ions due to their differing reactions with sulfate ions.
- Ba²⁺ (Barium ion) reacts with sulfate ions to form BaSO4 (Barium sulfate), which is a very insoluble white precipitate. This low solubility is a distinctive feature of Ba²⁺ in the presence of sulfate ions.
- Pb²⁺ (Lead(II) ion), on the other hand, forms PbSO4 (Lead(II) sulfate), which is also insoluble but to a lesser degree than BaSO4. However, PbSO4 is still slightly soluble in water and can be dissolved by excess potassium sulfate in some cases, especially in the presence of certain complexing agents.
So, when K2SO4 is added to a solution containing both Ba²⁺ and Pb²⁺, Ba²⁺ will immediately form a white precipitate of BaSO4, while Pb²⁺ will either form a very slight precipitate or remain in solution, depending on conditions. This allows you to distinguish between Ba²⁺ and Pb²⁺ based on the formation (or lack thereof) of the BaSO4 precipitate.
Why other reagents don’t work:
- A) KCl: Both Ba²⁺ and Pb²⁺ would form chloride salts, and both are soluble in water, so KCl wouldn’t distinguish them.
- B) Li2S2O3: Neither Pb²⁺ nor Ba²⁺ reacts distinctly with thiosulfate ions to form different precipitates or complexes.
- D) LiNO3: Both Ba²⁺ and Pb²⁺ form soluble nitrates with lithium, so no precipitation occurs.
Therefore, K2SO4 is the best reagent for distinguishing between Ba²⁺ and Pb²⁺.
