9.6 Acid Rain

• Formation of Acid Rain:

Non-metal oxides react with water to form various acids.

• Natural Sources:

• Pure air contains small amounts of carbon dioxide and other oxides of oxygen.

• Animals release carbon dioxide (CO2) during respiration.

• When lightning strikes, the temperature can reach up to 3000°C, causing nitrogen (N2) and oxygen (O2) in the air to react and form nitrogen oxide (NO).

• The NO is further oxidized by oxygen to form NO2.

• These oxides dissolve in rainwater, producing acids. This process results in acid rain.

• Example Reactions:

• CO2 (g) + H2O (l) → H2CO3 (aq) (Carbonic acid)

• 2NO (g) + H2O (l) → HNO3 (aq) + HNO2 (aq) (Nitric acid and nitrous acid)

• pH of Rainwater:

• Typically, rainwater has a pH value between 5 and 6. This is due to natural acids like carbonic acid and nitric acid.

• However, human activities can increase the amount of acids in rainwater.

• Human Impact on Acid Rain:

• Emissions from Vehicles, Power Plants, and Industries:

• Carbon dioxide (CO2) from vehicles, power plants, and industries mixes with air and reacts with rainwater, producing more carbonic acid (H2CO3).

• Combustion of Coal and Petroleum:

• Power plants, brick kilns, and other industries burning coal and petroleum release sulfur and nitrogen oxides, which react with water to form sulfuric acid and nitric acid.

• Acid Rain and Its Effects:

• In some areas, human activity leads to a higher concentration of acids in the rain, causing the pH of rainwater to drop to 4 or lower, which is considered acid rain.

• Effects on Soil:

• Acid rain lowers the pH of the soil, making it more acidic. This has harmful effects on crops and plants, damaging growth and fertility.

• Effects on Water Bodies:

• The pH of water bodies, such as rivers and lakes, can also decrease, making the environment inhospitable for aquatic life.

• Fish populations are harmed, and the overall ecosystem is disrupted.

• Damage to Infrastructure:

• Acid rain causes damage to buildings, metal structures, and marble sculptures. The acid reacts with materials, eroding surfaces and weakening structures over time.