4   2 This question is about the double salt K2Mg(SO4)2.6H2O. A double salt is a salt containing more than one cation or more than one anion. (a) (i) Give the reason why the term relative formula mass is used, rather than relative molecular mass, when discussing K2Mg(SO4)2.6H2O. (1) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (ii) Give the reason why relative formula mass has no mathematical units. 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(iii) What is the relative formula mass of K2Mg(SO4)2.6H2O? Use the Periodic Table as a source of data. (1) A 206.0 B 322.7 C 402.7 D 595.3 (iv) Calculate the amount of substance, in mol, in 25.0 g of K2Mg(SO4)2.6H2O. (1) Turn over 5   (b) Cations may be identified using a flame test on a solid or by the addition of aqueous sodium hydroxide to an aqueous solution containing the cation. Describe the expected results of performing these tests on K2Mg(SO4)2.6H2O. Include the observation for each cation in each test. 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(c) The test used to show the presence of the anion in K2Mg(SO4)2.6H2O gives a white precipitate as the positive result. (i) What are the reagents used for this test? (1) A dilute hydrochloric acid and aqueous silver nitrate B dilute sulfuric acid and aqueous silver nitrate C dilute hydrochloric acid and aqueous barium chloride D dilute sulfuric acid and aqueous barium chloride (ii) Write an ionic equation, including state symbols, for the formation of the white precipitate in the test for the anion in the double salt. (1) (Total for Question 2 = 10 marks)