Question

When the pH of rain water is above 5.6, then it is called acid rain.

(a) True

(b) False

I got this question in a national level competition.

This intriguing question originated from Environmental Chemistry in section Environmental Chemistry of Chemistry – Class 11

Answer 1

The correct answer is (b) False

The explanation is: On the pH scale, 7 is neutral; below 7 is said to be acidic and above 7 is said to be alkaline. Rain water normally has a pH of 5.6 due to the presence of H^+  ions formed by the reaction of rain water with carbon dioxide present in the atmosphere.When the pH of rain water falls below 5.6, then it is called as acid rain.

H2O (l) + CO2 (g)→ H2CO3 (aq)

H2CO3 (aq) → H^+ (aq) + HCO3^–(aq)