Gujarat BoardEnglish MediumSTD 11 ScienceChemistryEnvironmental Chemistry1 Mark
Question
Why does rain water normally have a pH of 5.6? When does it become acid rain?
✓
Answer
Rain has pH of about 5.6 due to dissolution of $\text{CO}_2$, gas in water.
$\text{CO}_2+\text{H}_2\text{O}\xrightarrow{\ \ \ \ \ \ \ \ \ }\text{H}_2\text{CO}_3$
$\text{H}_2\text{CO}_3\rightleftharpoons\text{2H}^++\text{CO}^{2-}_3$
When pH of rain falls below 5.6 it becomes acid rain.
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