CIE Jun 2014 v2 Paper 2 Q2

Answers available below

A 6.30 g sample of hydrated ethanedioic acid, H2C2O4.xH2O, was dissolved in water and the solution made up to 250 cm3. PMT A 25.0 cm3 sample of this solution was acidi ed and titrated with 0.100 mol dm3 potassium manganate(VII) solution. 20.0 cm3 of this potassium manganate(VII) solution was required to react fully with the ethanedioate ions, C2O4 2, present in the sample. (a) The MnO4ions in the potassium manganate(VII) oxidise the ethanedioate ions. (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 ethanedioate ions. 2MnO4 (aq) + 5C2O4 2(aq) + H+(aq)(aq) + 10CO2(aq) + H2O(l) [3] (b) (i) Calculate the number of moles of manganate(VII) used in the titration. (ii) Use the equation in (a)(ii) and your answer to (b)(i) to calculate the number of moles of C2O4 2 present in the 25.0 cm3 sample of solution used. [1] (iii) Calculate the number of moles of H2C2O4.xH2O in 6.30 g of the compound. (iv) Calculate the relative formula mass of H2C2O4.xH2O. (v) The relative formula mass of anhydrous ethanedioic acid, H2C2O4, is 90. Calculate the value of x in H2C2O4.xH2O. [1] [1] [1] [1] [Total: 9]UCLES 2014 9701/22/M/J/14<br />

Show answer