Sulphuric acid is manufactured by contact process.

(a) Give two balanced equations to obtain SO₂ in this process.

(b) Give the conditions for the oxidation of SO₂.

(c) Name the catalyst used.

(d) Why H₂SO₄ is not obtained by directly reacting SO₃ with water?

(e) Name the chemical used to dissolve SO₃ and also name the product formed. Give all the main reactions of this product.

(a) 4FeS₂ (iron pyrite) + 11O₂ ⟶ 2Fe₂O₃ + 8SO₂ ↑

S + O ⟶ SO₂ ↑

(b) The conditions for the oxidation of SO₂ are:

1. The temperature should be as low as possible. The yield has been found to be maximum at about 410 ⁰C – 450 ⁰C.
2. High pressure favours the reaction because the product formed has less volume than reactant. Pressure : 1 to 2 atmosphere.
3. Excess of oxygen increases the production of sulphur trioxide.

(c) Vanadium pentoxide [V₂O₅]

(d) Sulphuric acid is not obtained by directly reacting SO₃ with water since sulphur trioxide does not dissolve in water satisfactorily and it gives a lot of heat and forms misty droplets of sulphuric acid.

(e) The chemical used to dissolve SO₃ is concentrated sulphuric acid and the product formed is oleum.

Main reactions of this process are:

SO₃ + H₂SO₄ (conc.) ⟶ H₂S₂O₇ (oleum)

H₂S₂O₇ + H₂O ⟶ 2H₂SO₄