JEE Main · 2023 · 31 Jan 2023 · Shift 2 · Environmental Chemistry

The normal rain water is slightly acidic and its pH value is 5.6 because of which one of the following?

(A) $CO_{2} + H_{2} O \to H_{2} CO_{3}$ ✓ Correct
(B) $4 NO_{2} + O_{2} + 2 H_{2} O \to 4 HNO_{3}$
(C) $2 SO_{2} + O_{2} + 2 H_{2} O \to 2 H_{2} SO_{4}$
(D) $N_{2} O_{5} + H_{2} O \to 2 HNO_{3}$

Answer: (A)

Solution

Even clean, unpolluted rain dissolves atmospheric carbon dioxide, which combines with water as

C O_{2} + H_{2} O ⇌ H_{2} C O_{3}

. The weak carbonic acid so formed dissociates slightly to release hydrogen ions, holding the pH near 5.6. The reactions producing nitric and sulphuric acids describe acid rain, where the pH falls well below 5.6. The slight acidity of normal rain water is caused by dissolved carbon dioxide forming carbonic acid.

JEE Main · 2023 · 31 Jan 2023 · Shift 2 · Single correct option

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JEE Main · 2023 · 31 Jan 2023 · Shift 2 · Environmental Chemistry

Solution

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