CIE Jun 2014 v1 Paper 2 Q2

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The commonest form of iron(II) sulfate is the heptahydrate, FeSO4.7H2O. On heating at 90 C this loses some of its water of crystallisation to form a different hydrated form of iron(II) sulfate, FeSO4.xH2O. PMT 3.40 g of FeSO4.xH2O was dissolved in water to form 250 cm3 of solution. A 25.0 cm3 sample of this solution was acidi ed and titrated with 0.0200 mol dm3 potassium manganate(VII). In this titration 20.0 cm3 of this potassium manganate(VII) solution was required to react fully with the Fe2+ ions present in the sample. (a) The MnO4ions in the potassium manganate(VII) oxidise the Fe2+ ions in the acidi ed solution. (i) Explain, in terms of electron transfer, the meaning of the term oxidise in the sentence above.[1] (ii) Complete and balance the ionic equation for the reaction between the manganate(VII) ions and the iron(II) ions. MnO4 (aq) + 5Fe2+(aq) + H+(aq)(aq) + 5Fe3+(aq) + H2O(l) (b) (i) Calculate the number of moles of manganate(VII) used in the titration. [3] [1] (ii) Use the equation in (a)(ii) and your answer to (b)(i) to calculate the number of moles of Fe2+ present in the 25.0 cm3 sample of solution used. (iii) Calculate the number of moles of FeSO4.xH2O in 3.40 g of the compound. (iv) Calculate the relative formula mass of FeSO4.xH2O. (v) The relative formula mass of anhydrous iron(II) sulfate, FeSO4, is 151.8. Calculate the value of x in FeSO4.xH2O. [1] [1] [1] [1] [Total: 9]UCLES 2014 9701/21/M/J/14<br />

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