pH of acid rain is approximately

Options

A. 5.6
B. 6.2
C. 6.7
D. 7

Answer

To determine the approximate pH of acid rain, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Acid Rain**:
- Acid rain is formed when pollutants such as sulfur oxides (SOx) and nitrogen oxides (NOx) are released into the atmosphere from sources like automobile exhaust and industrial emissions. These substances react with water vapor and oxygen in the atmosphere.

2. **Chemical Reactions**:
- Sulfur dioxide (SO2) reacts with oxygen (O2) to form sulfur trioxide (SO3):
\[ 2SO2 + O2 \rightarrow 2SO3 \]
- Sulfur trioxide (SO3) then reacts with water vapor (H2O) to form sulfuric acid (H2SO4):
\[ SO3 + H2O \rightarrow H2SO4 \]
- Similarly, nitrogen dioxide (NO2) reacts with oxygen and water to form nitric acid (HNO3):
\[ 2NO2 + 1.5O2 + H2O \rightarrow 2HNO3 \]
- Carbon dioxide (CO2) reacts with water to form carbonic acid (H2CO3):
\[ CO2 + H2O \rightarrow H2CO3 \]

3. **Effect on pH**:
- The formation of these acids increases the concentration of hydrogen ions (H+) in the rainwater. The pH scale measures the concentration of hydrogen ions, where lower pH values indicate higher acidity.
- Normal rainwater has a pH of about 5.6 to 6.0, which is slightly acidic due to the presence of carbonic acid formed from CO2.

4. **pH of Acid Rain**:
- Acid rain typically has a pH ranging from approximately 4.2 to 5.5. This decrease in pH indicates a higher concentration of hydrogen ions compared to normal rainwater.

5. **Conclusion**:
- Therefore, the approximate pH of acid rain is around **4.2 to 5.5**.