IGCSE Chemistry 0620 Paper 4 Practice Paper: Periodic Table, Metal Extraction and Reactivity (Extended Theory, 100 marks)

Level: Year 10-11 (IGCSE) | Subject: Chemistry 0620 | Time: 60 minutes | Total: 100 marks | Parts: 38

Paper at a glance

Paper	Time	Marks	Calculator
Paper 4 (Extended, structured)	1 h 15 min	75	Not allowed

Questions

Question 1 (16 marks) – Periodic trends: reactivity of Group I and Group VII

(a) Write the balanced chemical equation for the reaction of sodium with water. (2 marks)

(b) 4.6 g of sodium reacts completely. Calculate the amount, in mol, of sodium. (2 marks)

(c) Calculate the volume of hydrogen formed in part (b) at room temperature and pressure (molar volume 24 dm3/mol). (3 marks)

(d) Explain why the reaction of Group I metals (lithium, sodium, potassium) with water becomes more vigorous down the group. (3 marks)

(e) Chlorine is bubbled into potassium bromide solution. Write the balanced equation and state which ion is oxidised. (3 marks)

(f) What volume, in cm3, of 0.50 mol/dm3 hydrochloric acid is needed to neutralise 0.20 mol of sodium hydroxide? (3 marks)

Question 2 (18 marks) – Reactivity series and the blast furnace extraction of iron

(a) Arrange potassium, zinc, iron and copper in order of decreasing reactivity. (2 marks)

(b) Explain why copper can occur uncombined in the Earth crust while sodium occurs only in compounds. (3 marks)

(c) Write the balanced equation for the reduction of iron(III) oxide by carbon monoxide in the blast furnace. (2 marks)

(d) Calculate the relative formula mass of Fe2O3 (Ar: Fe 56, O 16). (2 marks)

(e) 160 g of Fe2O3 is reduced completely. Calculate the mass of iron formed. (3 marks)

(f) In practice only 100 g of iron is obtained. Calculate the percentage yield to one decimal place. (3 marks)

(g) State the purpose of adding limestone to the blast furnace. (3 marks)

Question 3 (18 marks) – Electrolysis of molten aluminium oxide

(a) Write the equation for the reaction at the cathode during the electrolysis of molten aluminium oxide. (2 marks)

(b) Write the equation for the reaction at the anode. (2 marks)

(c) State the purpose of adding cryolite to the electrolyte. (2 marks)

(d) A current of 4.0 A is passed for 3600 s. Calculate the charge passed in coulombs. (3 marks)

(e) Calculate the amount, in mol, of electrons passed (1 mol of electrons carries 96500 C). (3 marks)

(f) Calculate the theoretical mass of aluminium produced (Ar: Al 27). (4 marks)

(g) Why is aluminium not extracted by electrolysing aqueous aluminium chloride? (2 marks)

Question 4 (16 marks) – Properties of metals, alloys and the oxide layer on aluminium

(a) Explain why an alloy is usually harder than the pure metal. (3 marks)

(b) State the difference between steel and pure iron. (2 marks)

(c) Which two metals make up brass? (2 marks)

(d) A block of aluminium has a volume of 40 cm3 and a density of 2.70 g/cm3. Calculate its mass. (3 marks)

(e) The block is oxidised completely: 4Al + 3O2 -> 2Al2O3. Calculate the mass of Al2O3 formed (Mr of Al2O3 = 102). (4 marks)

(f) Explain how the oxide layer protects an aluminium article. (2 marks)

Question 5 (16 marks) – Magnesium with dilute hydrochloric acid: rates and mole calculations

(a) Write the balanced equation for the reaction between magnesium and dilute hydrochloric acid. (2 marks)

(b) Calculate the amount, in mol, of magnesium in 0.50 g (Ar: Mg 24). (3 marks)

(c) Calculate the amount of HCl in 25.0 cm3 of 0.100 mol/dm3 hydrochloric acid, and use your answer to decide whether 0.50 g of magnesium is in excess. (3 marks)

(d) Calculate the volume of hydrogen produced (molar volume 24 dm3/mol), giving your answer in cm3. (4 marks)

(e) If magnesium powder is used instead of a magnesium ribbon, how does the rate change? Explain your answer. (2 marks)

(f) What effect does raising the temperature by 10 C have on the rate, and why? (2 marks)

Question 6 (16 marks) – Noble gases and reduction of copper(II) oxide by hydrogen

(a) Explain why argon is used as a shielding gas when welding metals. (2 marks)

(b) Explain why Group 0 elements have very low reactivity. (2 marks)

(c) Hydrogen is passed over heated copper(II) oxide. Write the balanced equation. (2 marks)

(d) 8.0 g of CuO is reduced completely. Calculate the theoretical mass of copper (Mr of CuO = 80, Ar of Cu = 64). (4 marks)

(e) The experiment gives 5.44 g of copper. Calculate the percentage yield to one decimal place. (3 marks)

(f) Give two reasons why hydrogen reduction is not used on a large scale to extract copper industrially. (3 marks)

Answers and marking notes

Question 1 – Periodic trends: reactivity of Group I and Group VII

(a) 2Na + 2H2O -> 2NaOH + H2 [2 marks]

(b) 4.6 / 23 = 0.20 mol. [2 marks]

(c) Mole ratio 2:1, so 0.10 mol H2; 0.10 x 24 = 2.4 dm3 (one mark ratio, one mark multiplication, one mark unit). [3 marks]

(d) (1) Atomic radius increases so the outer electron is further from the nucleus. (2) Shielding by inner electrons is greater, so the outer electron is lost more easily. (3) The metal is therefore a stronger reducing agent and reacts more vigorously with water. [3 marks]

(e) Cl2 + 2KBr -> 2KCl + Br2; the bromide ion (Br-) is oxidised to bromine (one mark equation, one mark products, one mark identification). [3 marks]

(f) NaOH + HCl -> NaCl + H2O, ratio 1:1, so 0.20 mol HCl is needed; 0.20 / 0.50 = 0.400 dm3 = 400 cm3. [3 marks]

Question 2 – Reactivity series and the blast furnace extraction of iron

(a) Potassium > zinc > iron > copper [2 marks]

(b) Copper is low in the reactivity series, below hydrogen, so it does not react readily with oxygen and water and can occur uncombined. Sodium is very reactive and reacts quickly with oxygen and water vapour in air, so it is found only in compounds. [3 marks]

(c) Fe2O3 + 3CO -> 2Fe + 3CO2 [2 marks]

(d) 2 x 56 + 3 x 16 = 160 [2 marks]

(e) 160 / 160 = 1.00 mol Fe2O3, giving 2.00 mol Fe; 2.00 x 56 = 112 g (one mark moles, one mark ratio, one mark mass). [3 marks]

(f) 100 / 112 x 100 = 89.3% [3 marks]

(g) Limestone (calcium carbonate) decomposes on heating to calcium oxide and carbon dioxide. The calcium oxide reacts with silica impurities in the ore to form slag, which floats on the molten iron and is run off. [3 marks]

Question 3 – Electrolysis of molten aluminium oxide

(a) Al3+ + 3e- -> Al [2 marks]

(b) 2O2- -> O2 + 4e- [2 marks]

(c) It lowers the melting point of aluminium oxide from about 2050 C to about 950 C, saving the energy needed for heating. [2 marks]

(d) Q = I x t = 4.0 x 3600 = 14400 C (one mark formula, one mark substitution, one mark answer). [3 marks]

(e) 14400 / 96500 = 0.149 mol. [3 marks]

(f) 3 mol electrons give 1 mol Al: 0.149 / 3 = 0.0497 mol; 0.0497 x 27 = 1.34 g (one mark ratio, one mark moles, one mark multiplication, one mark unit). [4 marks]

(g) In aqueous solution water is reduced more readily than aluminium ions, so hydrogen is released at the cathode and no aluminium is obtained. [2 marks]

Question 4 – Properties of metals, alloys and the oxide layer on aluminium

(a) An alloy contains atoms of different sizes, and these layers of different atoms prevent the layers from sliding over one another, so the alloy is harder and less easily deformed. [3 marks]

(b) Steel is an alloy of iron with carbon (and other elements), containing about 0.1 to 1.5 per cent carbon; pure iron contains almost no carbon and is softer. [2 marks]

(c) Copper and zinc [2 marks]

(d) 2.70 x 40 = 108 g [3 marks]

(e) 108 / 27 = 4.00 mol Al; ratio 4:2 gives 2.00 mol Al2O3; 2.00 x 102 = 204 g. [4 marks]

(f) A thin, adherent layer of aluminium oxide forms on the surface and prevents the metal beneath from reacting further with oxygen and water. [2 marks]

Question 5 – Magnesium with dilute hydrochloric acid: rates and mole calculations

(a) Mg + 2HCl -> MgCl2 + H2 [2 marks]

(b) 0.50 / 24 = 0.0208 mol. [3 marks]

(c) 0.100 x 25.0 / 1000 = 0.00250 mol HCl; only 0.00125 mol of magnesium (0.030 g) is needed, so 0.50 g is in excess. [3 marks]

(d) Ratio 2:1, so H2 = 0.00250 / 2 = 0.00125 mol; 0.00125 x 24 = 0.030 dm3 = 30 cm3. [4 marks]

(e) The rate increases because the powder has a larger surface area, so collisions between the metal and acid particles are more frequent. [2 marks]

(f) The rate increases noticeably because the particles have more kinetic energy and a greater proportion of collisions exceed the activation energy. [2 marks]

Question 6 – Noble gases and reduction of copper(II) oxide by hydrogen

(a) Argon is chemically unreactive, does not react with the hot metal, and excludes oxygen so the metal is not oxidised. [2 marks]

(b) Their outer electron shells are full (a complete octet, or two for helium), so they neither lose nor gain electrons. [2 marks]

(c) CuO + H2 -> Cu + H2O [2 marks]

(d) 8.0 / 80 = 0.100 mol CuO, giving 0.100 mol Cu; 0.100 x 64 = 6.40 g (one mark moles, one mark ratio, one mark multiplication, one mark unit). [4 marks]

(e) 5.44 / 6.40 x 100 = 85.0% [3 marks]

(f) Hydrogen is expensive and its storage and transport carry a risk of explosion; copper ores are processed more economically and on a larger scale by roasting and reduction, or by electrolysis. [3 marks]

Download

Question paper PDF · Answer key PDF

Book a tutor-led paper review →