Which of the following anion(s) can decolourise Br 2 water

Question

Which of the following anion(s) can decolourise Br 2 ​ water

TestHub · Accepted Answer

Explain the question: Identify anions that decolorize Br₂water.

Concept: Redox reactions of aqueous bromine.

Solution: Bromine water Br₂/H₂O is a reddish-brown solution that acts as a strong oxidizing agent. Anions that are reducing agents can react with it, reducing the colored Br₂ to colorless Br⁻ ions, thereby decolorizing the solution.

1. Sulfide (S²⁻): This ion is a strong reducing agent. It reacts with bromine water to form a yellow turbidity of elemental sulfur (S) while the solution becomes colorless.

$S^{2 -} (a q) + B r_{2} (a q) \to S (s) + 2 B r^{-} (a q)$

2. Sulfite (SO₃²⁻): It is readily oxidized to sulfate (SO₄²⁻) by bromine water. This process consumes the bromine and decolorizes the solution.

$S O_{3}^{2 -} (a q) + B r_{2} (a q) + H_{2} O (l) \to S O_{4}^{2 -} (a q) + 2 H B r (a q)$

3. Nitrite (NO₂⁻): Nitrite ions can also be oxidized to nitrate ions (NO₃⁻) by bromine water, resulting in the loss of the brown color.

$N O_{2}^{-} (a q) + B r_{2} (a q) + H_{2} O (l) \to N O_{3}^{-} (a q) + 2 H B r (a q)$

Since all three provided anions can reduce bromine, they all cause the brown color of bromine water to disappear.

Final Answer: Option (D).

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