OCR A Jun 2014 Paper 5 Q8

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8 A student carries out an investigation to prepare and analyse a sample of barium ferrate(VI), BaFeO4. The steps in the investigation are shown below. 18 Step 1 The student adds solid iron(III) oxide to a hot aqueous solution containing an excess of hydroxide ions. The student bubbles chlorine gas through the mixture. A solution forms containing aqueous ferrate(VI) ions, FeO4 2(aq), and aqueous chloride ions. Step 2 The student adds aqueous barium chloride to the resulting solution. A precipitate of impure barium ferrate(VI) forms. The precipitate is filtered, washed with distilled water and dried. The student obtains 0.437 g of impure solid barium ferrate(VI). Step 3 An excess of acidified aqueous potassium iodide is added to the solid from step 2. The BaFeO4 reacts as shown below, and the impurity does not react. A solution forms containing aqueous iodine, I2(aq). BaFeO4(s) + 8H+(aq) + 3I(aq) Fe3+(aq) + Ba2+(aq) + 1I2(aq) + 4H2O(l) Step 4 The student determines the amount of I2 formed by carrying out a titration with aqueous sodium thiosulfate, Na2S2O3(aq). 2S2O3 2(aq) + I2(aq) S4O6 2(aq) + 2I(aq) 26.4 cm3 of 0.100 mol dm3 Na2S2O3(aq) are required to reach the end point. (a) Construct an equation for the oxidation of iron(III) oxide (step 1).[2] (b) Write an ionic equation for the formation of barium ferrate(VI) (step 2). Include state symbols.[1]OCR 2014<br />
 (c) In step 3, what is the reducing agent? Explain your answer in terms of electrons. 19 reducing agentexplanation[2] (d) The solid sample of barium ferrate(VI) obtained in step 2 is impure. Determine the percentage, by mass, of barium ferrate(VI) in the 0.437 g of solid formed in step 2. Give your answer to one decimal place. percentage of barium ferrate(VI) =% [4] Question 8 continues on page 20OCR 2014 Turn over<br />
 (e) When the solution is not alkaline, ferrate(VI) ions react with water. The reaction forms a gas with a density of 1.333103 g cm3, measured at room temperature and pressure, and an orangebrown precipitate. 20Determine the formulae of the gas and the precipitate.Write an equation for the reaction that takes place. gasprecipitateequation[3] [Total: 12] END OF QUESTION PAPEROCR 2014<br />

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