14 6 Malachite is a green mineral with the formula Cu2CO3(OH)2 . It has a molar mass of 221 g mol–1. (a) What is the percentage by mass of copper in pure malachite? (1) A 40.3% B 51.4% C 57.5% D 67.9% (b) Describe what you would expect to see when an excess of dilute hydrochloric acid is added to a sample of pure solid malachite. 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(c) (i) Describe how you would carry out a flame test on a sample of powdered malachite. (3) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 15 Turn over (ii) When the atoms of some elements are heated, they produce a characteristic flame colour. For example, the copper in malachite gives a blue-green colour. Explain how atoms of different elements can produce different characteristic flame colours when heated. (4) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 16 (d) (i) When malachite is heated to approximately 300 °C, water, carbon dioxide and copper(II) oxide are formed. The equation for this decomposition is Cu2CO3(OH)2 → 2CuO + CO2 + H2O Calculate the maximum volume of carbon dioxide that could be produced when 0.810 g of malachite is thermally decomposed. Assume that the gas is collected at a temperature of 25 °C and 101 kPa pressure. Give your answer to an appropriate number of significant figures and state the units. [The ideal gas equation is pV = nRT. Gas constant (R) = 8.31 J mol–1 K–1] (5) (ii) The gas was collected in a gas syringe with a stated accuracy of ± 0.5 cm3. Calculate the percentage uncertainty in the volume of gas collected. (1) 17 Turn over (iii) Malachite ore is a mixture of malachite and rock. A 0.810 g sample of malachite ore was thermally decomposed, producing 0.571 g of copper(II) oxide. Calculate the percentage purity of this malachite ore sample. Give your answer to an appropriate number of significant figures. (3) (Total for Question 6 = 20 marks)