7.1.5Acids, Bases and Salts
Acid Rain: Nitrogen Oxides and Sulfur Dioxide — Cambridge IGCSE Chemistry 0620 Revision Notes & Topical Questions
5 min read 6 parts Lesson 2 of 11 Unit quiz
Curriculum Equation Key pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: pH + pOH = 14
Section 1 of 6Where the gases come from
Sulfur dioxide
- Sulfur dioxide Fossil fuels, especially coal, contain sulfur impurities that are oxidised when the fuel burns: S(s) + O2(g) → SO2(g).
- It is a colourless gas with a sharp smell.
Nitrogen oxides
- Nitrogen oxides In a hot car engine, nitrogen and oxygen from the air react to form nitrogen monoxide and nitrogen dioxide.
- Lightning does the same naturally.
Acidic oxides
- Acidic oxides Both sulfur dioxide and nitrogen dioxide are non-metal oxides, which form acidic solutions in water.
Section 2 of 6How acid rain forms
1Gases released
- Gases released Burning fuels sends sulfur dioxide and nitrogen oxides into the air.
2Dissolve in cloud droplets
- Dissolve in cloud droplets They dissolve in water droplets, with oxygen present, to make acids.
3Acids form
- Acids form 2SO2 + O2 + 2H2O → 2H2SO4 (sulfuric acid); 4NO2 + 2H2O + O2 → 4HNO3 (nitric acid).
4Rain falls
- Rain falls Droplets grow, become heavy and fall as acid rain, which can be carried a long way by the wind.
Section 3 of 6Effects of acid rain
| Affected | Damage |
|---|---|
| Buildings and statues | Carbonate rocks such as limestone and marble are dissolved or eroded |
| Metal structures | Corrosion of bridges, railings and cars |
| Lakes and rivers | Lower pH harms fish and other aquatic organisms |
| Soil and trees | Nutrients are washed away and metal ions that harm roots are released |
| People | Gases irritate eyes, throats and lungs |
Section 4 of 6Reducing the problem
Cutting acid gases
Remove sulfur
- Remove sulfur Take sulfur out of fuels before burning,
- or remove sulfur dioxide from power station gases with a scrubber using calcium oxide or limestone.
Catalytic converters
- Catalytic converters Fitted to car exhausts, they convert nitrogen oxides into nitrogen and oxygen.
Use alternatives
- Use alternatives Using less fossil fuel, or cleaner energy sources, produces fewer acid gases.
Section 5 of 6Key terms
| Term | Meaning |
|---|---|
| Acid rain | Rain made more acidic by dissolved sulfur dioxide and nitrogen oxides. |
| Sulfur dioxide | SO2, a pollutant gas made when sulfur-containing fuels burn. |
| Nitrogen oxides | Oxides of nitrogen, such as NO and NO2, formed at high temperatures. |
| Pollutant | A substance in the environment that causes harm. |
| Catalytic converter | A device in an exhaust system that converts harmful gases into less harmful ones. |
Section 6 of 6Exam technique
1
Saying that carbon dioxide is the main cause of acid rain; it is mainly sulfur dioxide and nitrogen oxides.
2
Writing that nitrogen oxides come from the fuel; they come from the air in hot engines.
3
Describing the effects only as 'damage' without naming what is damaged and how.
4
Confusing acid rain with global warming; they are different environmental problems.
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