Sulphur and Its Oxides — So3 and Acid Rain

Acid-rain school pathway (sulphur): SO₂ → SO₃ → H₂SO₄. Sources of SO₂: burning sulphur-containing fuels / ores (school). Extra acid: nitric acid from NOx also contributes. Same oxide names appear in Contact Process industrially, but here the application is unwanted environmental acid — still do not blame CO₂ as the main cause.

Acid rain is the environmental sequel to sulphur oxide chemistry. Step 1 — SO₂. Combustion of coal and other sulphur-bearing fuels releases sulphur dioxide into the air. Step 2 — SO₃. In the atmosphere, SO₂ can be oxidised further to sulphur trioxide SO₃ (school wording; catalysts/particulates may be mentioned in wider air chapters). Step 3 — H₂SO₄. SO₃ interacts with water to give sulphuric acid, which falls as acid rain or deposits as acidic pollution. Nitric contribution. Parallel NOx chemistry forms nitric acid, so acid deposition is not only sulphuric. Always allow both S and N acids when the question says acid rain broadly. Industrial echo. Contact Process also uses SO₂ → SO₃ → H₂SO₄ on purpose in a factory. In acid-rain answers, stress pollution and damage, not fertiliser pride. Still keep CO₂ out as the main cause. Exam skeleton: source of SO₂ → oxidation to SO₃ → H₂SO₄ in rain → harm; add HNO₃ from NOx if marks allow.

SO₂ from burning dirty fuels can become SO₃. SO₃ leads to sulphuric acid H₂SO₄ in acid rain. Nitric acid from NOx also makes rain acidic. Remember: SO₂ → SO₃ → H₂SO₄.

Write the three-step sulphur path with formulas. Add one formation source for SO₂ and one environmental harm. Include nitric acid from NOx as a second contributor. Contrast briefly with industrial Contact (same chemistry, different intent) without inventing plant pressures unless asked.

In longer answers, name wet deposition (acid rain) and mention dry deposition of acidic gases if the syllabus does. Separate strong-acid rain (H₂SO₄, HNO₃) from weak carbonic acid from CO₂. Link prevention slogans (low-sulphur fuel, scrubbers) only when asked — this topic’s core is the oxide pathway.

SO₂ → SO₃ → H₂SO₄ (acid rain). NOx → HNO₃ also contributes. Not mainly CO₂.