6.3 — The Contact Process: Basics
Cambridge IGCSE Chemistry 0620 · Paper 4 Style · 34 Total Marks
⚠️ Examiner's Note
Read each question carefully. Use state symbols in all equations. The reversible sign ⇌ is NOT optional — using → loses a mark. Show ALL working in calculations.
Write the balanced symbol equation for the main reversible stage of the Contact process.
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What type of reaction is represented by the ⇌ symbol in the Contact process equation?
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Identify the oxidation state of sulfur in SO₂ and in SO₃. What type of change does sulfur undergo in the forward reaction?
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State the catalyst used in the Contact process and the typical temperature and pressure conditions.
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Explain why a compromise temperature of ~450°C is chosen rather than a very low or very high temperature.
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State TWO ways of obtaining the sulfur dioxide needed for the Contact process.
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Where is the oxygen obtained from for the Contact process?
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Write the balanced symbol equation for the burning of sulfur to produce sulfur dioxide.
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Suggest why the gases entering the Contact process reactor must be purified before reaching the catalyst.
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After SO₃ is produced, it is NOT dissolved directly in water to make sulfuric acid. Explain why, and state what it is dissolved in instead.
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How many moles of gas are on the REACTANT side of the equation: 2SO₂(g) + O₂(g) ⇌ 2SO₃(g)?
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How many moles of gas are on the PRODUCT side? What does this tell you about the effect of pressure on the equilibrium position?
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Calculate the mass of SO₃ produced when 6.4 g of sulfur is burned completely and the SO₂ is fully converted to SO₃. (Ar: S = 32, O = 16)
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In the Contact process, the conversion of SO₂ to SO₃ is only about 99.5% efficient. Suggest what happens to the unreacted SO₂ and why this is environmentally important.
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Outline the complete Contact process from raw materials to concentrated sulfuric acid. Include equations at each stage. [Extended Writing — 5 marks]
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📊 Your Score Summary
🔁 Revisit the Contact Process lesson and focus on stoichiometry and conditions.
Section A
0/11
Section B
0/9
Section C
0/14
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