12.1.5—Role of NO and NO2 in the formation of acid
- Syllabus
- 9701–2028–2029
- Objective
- 12.1.5
- Level
- AS
NO and NO₂ help convert sulfur dioxide into sulfuric acid in the atmosphere
Sulfur dioxide can be oxidised in air to sulfur trioxide and then hydrated to sulfuric acid. NO and NO₂ participate in the catalytic oxidation pathway, so nitrogen oxides can accelerate acid formation without being consumed overall.
Separate direct acid formation from catalytic regeneration: NO₂ can oxidise SO₂ while being reduced to NO, and atmospheric oxidants then regenerate NO₂. The net effect links combustion emissions to acid deposition.
A simplified sequence is SO₂ + NO₂ → SO₃ + NO followed by SO₃ + H₂O → H₂SO₄. The first equation alone is not the whole atmospheric mechanism.
NOx are not the only source of acid rain, and “catalytic” does not mean nitrogen oxides disappear. Track the cycle and the sulfur-containing product.
ConceptA-Level CAIE Chemistry AS