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ChemistryYear 11English

Cambridge IGCSE Chemistry 0620 Paper 4 Extended Sample — 2020

Electrolysis and redox reactions are two sides of the same coin—yet most Year 11 chemists mix them up on exam day. This paper builds your confidence in writing half-equations, predicting electrode products, and spotting oxidation state changes in context. You'll encounter calculations with moles and empirical formulae, energy changes via bond enthalpies, and the equilibrium shifts you need to explain Le Chatelier scenes without hesitation. All questions mirror the extended-response style of Cambridge Paper 4: short stems, high marks per question, and examiners hunting for evidence of deep understanding rather than rote memory. By the end, you'll have a mental checklist for balancing redox, calculating theoretical yields, and defending why a process shifts the way it does.

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  1. Question 1

    Which of the following is the correct ionic equation for the electrolysis of dilute sulfuric acid?

  2. Question 2

    In the electrolysis of molten lead bromide, lead is formed at the cathode. What is the oxidation state change of lead and which substance is oxidised?

  3. Question 3

    A compound contains 40% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. What is its empirical formula? (Ar: C = 12, H = 1, O = 16)

  4. Question 4

    A student reacts 8 g of magnesium with excess oxygen. How many moles of magnesium were reacted? (Ar: Mg = 24)

  5. Question 5

    Which statement correctly describes a redox reaction?

  6. Question 6

    Use bond energies to calculate the enthalpy change for the reaction H2(g)+Cl2(g)→2HCl(g)\text{H}_2(g) + \text{Cl}_2(g) \rightarrow 2\text{HCl}(g). (Bond energies: H–H = 436 kJ/mol, Cl–Cl = 243 kJ/mol, H–Cl = 431 kJ/mol)

  7. Question 7

    In a reversible reaction at equilibrium, the concentration of product increases. What effect does this have on the equilibrium position?

  8. Question 8

    For the Haber process: N2(g)+3H2(g)⇌2NH3(g)\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g), which conditions favour the forward reaction?

  9. Question 9

    A solution of sodium chloride is electrolysed using inert electrodes. At the cathode, the only product is hydrogen gas. Which species is reduced at the cathode?

  10. Question 10

    25 cm³ of 0.1 mol/dm³ sodium hydroxide is neutralised by 20 cm³ of hydrochloric acid. What is the concentration of the hydrochloric acid?

  11. Question 11

    In an experiment, hydrogen and iodine react to form hydrogen iodide: H2(g)+I2(g)⇌2HI(g)\text{H}_2(g) + \text{I}_2(g) \rightleftharpoons 2\text{HI}(g). If the temperature is increased, how does this affect the forward and backward reaction rates?

  12. Question 12

    Copper can be oxidised by concentrated sulfuric acid. Write a balanced ionic equation for this redox reaction, in which copper is oxidised to Cu²⁺ and sulfuric acid is reduced to SO₂.

  13. Question 13

    In the Contact process for sulfuric acid manufacture, sulfur dioxide is oxidised to sulfur trioxide using vanadium(V) oxide as a catalyst. What is the oxidation state of vanadium in the catalyst?