6   3 A group of students design and carry out experiments to deduce the formulae of two salts, X and Y. X contains one cation and one anion. Y contains water of crystallisation. (a) (i) A flame test is carried out on X. Describe how to carry out a flame test. (3) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (ii) The colour of the flame is yellow. Give the formula of the metal ion present in salt X. (1) .................................................................................................................................................................................................................................................................................... (b) A sample of X is placed in a test tube and dissolved in deionised water. The solution is acidified with hydrochloric acid and barium chloride solution is added. A white precipitate forms. (i) Give the formula of the anion present in X. (1) .................................................................................................................................................................................................................................................................................... (ii) Deduce the formula of X, using your answers to (a)(ii) and (b)(i). (1) .................................................................................................................................................................................................................................................................................... Turn over 7   (c) Y is identified as hydrated potassium carbonate, K2CO3·nH2O. Two of the students were asked to determine the number of moles of water of crystallisation, n, in Y using the procedure shown: • weigh a sample of hydrated Y into a pre‑weighed crucible • place a lid loosely on the crucible and heat it for five minutes to remove the water of crystallisation • allow the crucible and lid to cool, remove the lid and then reweigh the crucible with its contents. lid crucible heat hydrated Y pipeclay triangle (i) The first student carried out the experiment but forgot to use the lid. Explain how this mistake would affect the calculated value of n. 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(ii) The second student carried out the experiment but heated the apparatus for only one minute. Explain how this mistake would affect the calculated value of n. (2) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 8   (iii) In an accurate experiment, Y is found to consist of 71.9 % K2CO3 by mass. Calculate the value of n. (3) (Total for Question 3 = 13 marks) Turn over 9   BLANK PAGE