AQA Jun 2017 Paper 1 Q11

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1 1 1 1 . 1 *23* 23This question is about compounds containing ethanedioate ions. A white solid is a mixture of sodium ethanedioate (Na2C2O4), ethanedioic acid dihydrate (H2C2O4.2H2O) and an inert solid. A volumetric flask contained 1.90 g of this solid mixture in 250 cm3 of aqueous solution. Two different titrations were carried out using this solution. In the first titration 25.0 cm3 of the solution were added to an excess of sulfuric acid in a conical flask. The flask and contents were heated to 60 oC and then titrated with a 0.0200 mol dm3 solution of potassium manganate(VII). When 26.50 cm3 of potassium manganate(VII) had been added the solution changed colour. The equation for this reaction is 2MnO4+ 5C2O4 2 + 16H+2Mn2+ + 8H2O + 10CO2 In the second titration 25.0 cm3 of the solution were titrated with a 0.100 mol dm3 solution of sodium hydroxide using phenolphthalein as an indicator. The indicator changed colour after the addition of 10.45 cm3 of sodium hydroxide solution. The equation for this reaction is H2C2O4 + 2OHC2O4 2 + 2H2O Calculate the percentage by mass of sodium ethanedioate in the white solid. Give your answer to the appropriate number of significant figures. Show your working. [8 marks] Turn overIB/M/Jun17/7405/1<br /> 24*24* Percentage by mass of sodium ethanedioate IB/M/Jun17/7405/1<br /> Bond angle Type of isomerism 1 1 1 1 . 4 25Ethanedioate ions react with aqueous iron(III) ions in a ligand substitution reaction. Write an equation for this reaction. Suggest why the value of the enthalpy change for this reaction is close to zero. [2 marks] 1 1 . 2 . 3 Draw the displayed formula of the iron complex produced in the reaction in Question 11.2 Indicate the value of the OFeO bond angle. State the type of isomerism shown by the iron complex. [3 marks] Ethanedioate ions are poisonous because they react with iron ions in the body. Ethanedioate ions are present in foods such as broccoli and spinach. Suggest one reason why people who eat these foods do not suffer from poisoning. [1 mark] *25* END OF QUESTIONS 14 Turn overIB/M/Jun17/7405/1<br />

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