ℹ️ Enrichment / Legacy Topic
This topic is no longer part of the core syllabus for examinations from 2025 onwards. It is provided here as enrichment material.
📘 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.
Study this topic on the go
Get flashcards and quizzes in ChemEasy, or plan your revision with ChemPlan IB.