📘 IB Understanding
Combustion of fossil fuels releases non-metal oxides (SO2, NOx) into the atmosphere. These react with water to form acid rain with a pH below 5.6.
Sources of Acid Rain
- Sulfur dioxide (SO2) - from burning coal and oil containing sulfur impurities
- Nitrogen oxides (NOx) - formed when N2 and O2 react at the high temperatures inside vehicle engines and power stations
Key Equations
Formation of Acids
- SO2(g) + H2O(l) → H2SO3(aq) (sulfurous acid)
- SO3(g) + H2O(l) → H2SO4(aq) (sulfuric acid)
- 2NO2(g) + H2O(l) → HNO2(aq) + HNO3(aq) (nitrous + nitric acid)
Environmental Effects
| Effect | Detail |
|---|---|
| Lakes & rivers | Acidification kills fish and aquatic organisms |
| Soil | Leaches essential minerals (Ca2+, Mg2+) and releases toxic Al3+ ions |
| Buildings | Corrodes limestone (CaCO3) and marble structures |
| Forests | Damages leaves and weakens trees |
| Metals | Accelerates corrosion of iron and steel structures |
Prevention
- Catalytic converters in vehicles reduce NOx emissions
- Flue gas desulfurisation removes SO2 from power station exhaust using CaCO3
- Liming acidic lakes with CaCO3 neutralises the acid
- Switching to renewable or low-sulfur fuels
⚠️ Exam Tip
IB questions frequently ask you to write the balanced equations showing how SO2, SO3, and NO2 react with water. Make sure you can recall all three.