Total marks: 80 · Duration: 75 minutes · Tier: Extended
Instructions to candidates
- Answer all questions.
- Use a black or dark blue pen. You may use an HB pencil for any diagrams or graphs.
- Write your answers in the spaces provided.
- You may use a calculator.
- Where a question describes apparatus in words, you may find it helpful to sketch it.
Information
- The total mark for this paper is 80.
- The number of marks for each question or part question is shown in brackets.
- This paper covers the Core and Supplement content of the Cambridge IGCSE Chemistry (0620) syllabus.
- Relative atomic masses (Ar): H = 1, C = 12, N = 14, O = 16, Na = 23, S = 32.
- The volume of one mole of any gas is 24 dm³ at room temperature and pressure (r.t.p.).
Paper
Question 1 — Atomic structure and bonding (11 marks)
(a) A strontium ion is represented as ⁸⁸₃₈Sr²⁺. Give the number of protons, neutrons and electrons in this ion. [2 marks]
(b) Define the term isotopes. [1 mark]
(c) Gallium has two isotopes: 60.1% gallium-69 and 39.9% gallium-71. Calculate the relative atomic mass of gallium. Give your answer to 1 decimal place. [2 marks]
(d) Explain why solid sodium chloride does not conduct electricity but molten sodium chloride does. [2 marks]
(e) Describe the covalent bonding in a nitrogen molecule, N₂. [1 mark]
(f) Explain why metals are malleable. Refer to the structure of a metal in your answer. [2 marks]
(g) Silicon(IV) oxide has a structure similar to diamond. Give one similarity between the structures of silicon(IV) oxide and diamond. [1 mark]
Question 2 — Stoichiometry (12 marks)
(a) Calculate the percentage by mass of nitrogen in ammonium nitrate, NH₄NO₃. [2 marks]
(b) A compound contains 40.0% carbon, 6.7% hydrogen and 53.3% oxygen by mass.
(i) Calculate the empirical formula of the compound. [2 marks]
(ii) The relative molecular mass of the compound is 180. Deduce its molecular formula. [1 mark]
(c) 25.0 cm³ of sodium carbonate solution is titrated with 0.125 mol/dm³ sulfuric acid. 20.0 cm³ of the acid is needed for neutralisation.
Na₂CO₃ + H₂SO₄ → Na₂SO₄ + H₂O + CO₂
(i) Calculate the concentration of the sodium carbonate solution in mol/dm³. [3 marks]
(ii) Convert your answer to (c)(i) into g/dm³. [1 mark]
(d) Calculate the volume of carbon dioxide, at r.t.p., produced in the titration in part (c). Give your answer in dm³. [1 mark]
(e) In another experiment, the theoretical yield of a product is 4.0 g. The actual yield is 3.4 g. Calculate the percentage yield. [2 marks]
Question 3 — Electrochemistry (11 marks)
(a) Concentrated aqueous sodium chloride is electrolysed using inert electrodes.
(i) Name the product at the anode and the product at the cathode. [2 marks]
(ii) Write an ionic half-equation for the reaction at the cathode. [1 mark]
(iii) Explain why the solution becomes alkaline during the electrolysis. [1 mark]
(b) When dilute aqueous sodium chloride is electrolysed, a different product forms at the anode. Name this product. [1 mark]
(c) Describe how an iron key could be electroplated with silver. In your answer, name the electrodes and the electrolyte. [3 marks]
(d) A hydrogen–oxygen fuel cell is used to power a car.
(i) Write the overall equation for the reaction in a hydrogen–oxygen fuel cell. [1 mark]
(ii) Give one advantage of using a fuel cell rather than a petrol engine. [1 mark]
(iii) Give one disadvantage of using a fuel cell rather than a petrol engine. [1 mark]
Question 4 — Energetics, rates and equilibrium (13 marks)
(a) Hydrogen reacts with bromine: H₂ + Br₂ → 2HBr
| Bond | Bond energy (kJ/mol) |
|---|---|
| H–H | 436 |
| Br–Br | 193 |
| H–Br | 366 |
Calculate the energy change for this reaction. [3 marks]
(b) A student investigates how the concentration of hydrochloric acid affects the rate of its reaction with marble chips.
(i) Name a piece of apparatus that could be used to measure the volume of carbon dioxide produced. [1 mark]
(ii) Explain, using collision theory, why the rate increases when the concentration of the acid increases. [2 marks]
(c) Explain how a catalyst increases the rate of a reaction. [1 mark]
(d) In the Contact process, sulfur trioxide is made from sulfur dioxide:
2SO₂(g) + O₂(g) ⇌ 2SO₃(g) ΔH = −196 kJ/mol
(i) Name the catalyst used. [1 mark]
(ii) State and explain the effect of increasing the temperature on the position of equilibrium. [2 marks]
(iii) Increasing the pressure would increase the yield of sulfur trioxide, but a pressure of only about 200 kPa is used. Suggest two reasons why. [2 marks]
(iv) State the condition needed for a reversible reaction to reach equilibrium. [1 mark]
Question 5 — Acids, bases, salts and identifying ions (11 marks)
(a) Define an acid in terms of proton transfer. [1 mark]
(b) Ethanoic acid is a weak acid. Explain what is meant by a weak acid. [1 mark]
(c) Barium sulfate is an insoluble salt. It is made by mixing aqueous barium chloride and aqueous sodium sulfate.
(i) Write the ionic equation, with state symbols, for the formation of barium sulfate. [1 mark]
(ii) Describe how a pure, dry sample of barium sulfate could be obtained from the mixture. [2 marks]
(d) (i) Aqueous sodium hydroxide is added to solution X. A green precipitate forms, which is insoluble in excess. Identify the cation in X. [1 mark]
(ii) Dilute nitric acid and aqueous silver nitrate are added to solution Y. A cream precipitate forms. Identify the anion in Y. [1 mark]
(iii) Describe a test for ammonium ions. Give the result. [2 marks]
(e) Zinc oxide is an amphoteric oxide.
(i) What is meant by an amphoteric oxide? [1 mark]
(ii) Name one other amphoteric oxide. [1 mark]
Question 6 — Metals, the Periodic Table and the environment (10 marks)
(a) Rubidium is in Group I, below potassium. Predict how rubidium reacts with water, and explain your prediction. [2 marks]
(b) Iron is extracted from hematite, Fe₂O₃, in a blast furnace. Write a balanced equation for each of these reactions.
(i) Coke (carbon) burns in air. [1 mark]
(ii) Carbon dioxide reacts with more coke to form carbon monoxide. [1 mark]
(iii) Carbon monoxide reduces iron(III) oxide to iron. [1 mark]
(c) Explain the role of limestone in the blast furnace. Include an equation for the formation of slag. [2 marks]
(d) Name the two substances needed for iron to rust. [1 mark]
(e) A catalytic converter removes carbon monoxide and nitrogen monoxide from car exhaust gases. Write a balanced equation for the reaction between these two gases. [2 marks]
Question 7 — Organic chemistry (12 marks)
(a) Give two characteristics of a homologous series. [2 marks]
(b) Ethanol is manufactured by the catalytic addition of steam to ethene.
(i) Give the conditions used for this process. [2 marks]
(ii) Give one advantage of making ethanol by fermentation instead. [1 mark]
(c) (i) Name the ester formed when methanol reacts with propanoic acid. [1 mark]
(ii) Give the structural formula of this ester. [1 mark]
(d) (i) Give the structure of the repeat unit of poly(propene). [1 mark]
(ii) Name the small molecule eliminated when a polyester such as PET forms. [1 mark]
(e) Butane, C₄H₁₀, has a structural isomer. Name butane's isomer and explain why the two compounds are structural isomers. [2 marks]
(f) Describe a test to distinguish between ethane and ethene. Give the result for each. [1 mark]