32 (A410U10-1) © WJEC CBAC Ltd. 13. A student is given several magnesium compounds containing common anions and designs the scheme below to identify the anion present in each compound. no no no no no no no yes yes yes A C B D E F G yes yes yes yes does it dissolve in water? barium chloride solution is added to a sample of the solution does it give a white precipitate? silver nitrate solution is added to a sample of the solution does it give a precipitate? concentrated ammonia solution is added to the precipitate does the precipitate dissolve completely? does it dissolve in hydrochloric acid? does it fizz as it dissolves? nitrate anions present is the precipitate white? (A410U10-1) © WJEC CBAC Ltd. Turn over. (a) The student labels seven possible results as A-G. He is able to suggest likely identities for anions that would give six of these results, and his teacher said that none of the common anions that he had studied would give the seventh result. Suggest possible anions for six of the seven results below. Write ‘UNKNOWN’ for the result that would not correspond to a common anion. [4] A …………………………...................................................................………………………… B …………………………...................................................................………………………… C …………………………...................................................................………………………… D …………………………...................................................................………………………… E …………………………...................................................................………………………… F …………………………...................................................................………………………… G …………………………...................................................................………………………… (b) The planned method would not be suitable for identifying all these anions in sodium compounds. Explain why the method would not be suitable and suggest how it could be modified to make it suitable. [3] (c) Concentrated aqueous ammonia solution at 298 K contains 31.0 % ammonia by mass. The density of this solution is 0.900 g cm–3. Calculate the concentration of this solution in mol dm–3. [3] Concentration = ………............................………………… mol dm–3 33 Examiner only (A410U10-1) (d) The student is provided with a solution containing chloride as the only anion. He is told that the solution also contains sodium ions, magnesium ions, or a mixture of both sodium and magnesium ions. He proposes using a flame test to identify the cation(s) present in the mixture. State the observations expected for each possibility and explain whether this method would be appropriate. [3] END OF PAPER © WJEC CBAC Ltd. 34 Examiner only 13 (A410U10-1) Turn over. 35 Examiner only © WJEC CBAC Ltd. Additional page. (A410U10-1) 36 Examiner only © WJEC CBAC Ltd. Additional page.