Question

Why does rain water have pH less than 7 ?

Answer 1

Carbon dioxide reacts with water to form weak carbonic acid which is slightly acidic having pH about 5.6.
Hence, the pH of rain water usually ranges between 5.6 and 3.5; at times, it can be as low as 2.
Normal rain is only slightly acidic having pH about 5.6.
This is because carbon dioxide reacts with it to form weak carbonic acid.
CO₂ + H₂O → H₂CO₃
pH of acid rain usually ranges between 5.6 and 3.5; at times, it can be as low as 2.