CIE Jun 2015 v1 Paper 3 Q1

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In this question you will determine the concentration of iron(II) ions in FA 2. To do this you will do a titration using potassium manganate(VII) solution. The iron(II) ions, Fe2+, are oxidised by the manganate(VII) ions, MnO4 . 5Fe2+(aq) + MnO4 (aq) + 8H+(aq)5Fe3+(aq) + Mn2+(aq) + 4H2O(l) When all the Fe2+ ions have been oxidised, the presence of unreacted MnO4 solution to become a permanent pink colour.ions causes the FA 1 contains 0.0200 mol dm3 manganate(VII) ions, MnO4 FA 2 is a solution containing iron(II) ions, Fe2+. FA 3 is 1.0 mol dm3 sulfuric acid, H2SO4. . (a) MethodFill the burette with FA 1. Use the pipette to transfer 25.0 cm3 of FA 2 into the conical flask. Use the 25 cm3 measuring cylinder to add 10 cm3 of FA 3 to the conical flask. Add FA 1 from the burette into the conical flask until the solution becomes a permanent pink colour. Perform a rough titration and record your burette readings in the space below. The rough titre iscm3.Do as many accurate titrations as you think necessary to obtain consistent results. Make certain any recorded results show the precision of your practical work. Record in a suitable form below all of your burette readings and the volume of FA 1 added in each accurate titration. Keep FA 2 to use in Question 3. II III IV VI VII [7]UCLES 2015 9701/31/M/J/15<br /> (b) From your accurate titration results, obtain a suitable value to be used in your calculations. Show clearly how you obtained this value. 25.0 cm3 of FA 2 requiredcm3 of FA 1. [1] (c) Calculations Show your working and appropriate signi cantgures in thenal answer to each step of your calculations. (i) Calculate the number of moles of manganate(VII) ions present in the volume of FA 1 calculated in (b). (ii) Calculate the number of moles of iron(II) ions present in 25.0 cm3 of FA 2. moles of MnO4=mol (iii) Calculate the concentration, in mol dm3, of iron(II) ions in FA 2. moles of Fe2+ =mol concentration of Fe2+ in FA 2 =mol dm3 (iv) FA 2 was prepared by dissolving hydrated ammonium iron(II) sulfate, (NH4)2Fe(SO4)2.6H2O in distilled water. Calculate the mass of salt that would have to be dissolved in 1.00 dm3 of water to prepare FA 2. (Ar: H, 1.0; N, 14.0; O, 16.0; S, 32.1; Fe, 55.8) II III IV mass of (NH4)2Fe(SO4)2.6H2O =g [4]UCLES 2015 9701/31/M/J/15 [Total: 12] [Turn over<br />

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