2019 TJC H2 Chem Prelim P4 QP

2 DO NOT WRITE IN THIS MARGIN [Turn over DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2019 DO NOT WRITE IN THIS MARGIN Answer all the questions in the spaces provided. 1 Determination of the concentration of a solution of hydrogen peroxide Hydrogen peroxide, H 2O2, can be oxidised to give oxygen, O 2. This reaction happens rapidly in the presence of acidified potassium manganate(VII), KMnO4. 2MnO4͞ (aq) + 5H2O2(aq) + 6H+(aq) 2Mn2+(aq) + 5O2(g) + 8H2O(l) To determine the concentration of a solution of hydrogen peroxide, y ou will first dilute the solution and then carry out a titration using acidified potassium manganate(VII), KMnO4. FA 1 is aqueous hydrogen peroxide. FA 2 is 0.0200 mol dm-3 potassium manganate(VII), KMnO4. FA 3 is 1.0 mol dm-3 sulfuric acid, H2SO4. Keep FA 1 for use in Question 3 (a) Method Dilution ● Pipette 25.0 cm3 of FA 1 into the 250 cm3 volumetric flask. ● Add distilled water to make 250 cm3 of solution and shake the flask thoroughly. ● Label this diluted solution of hydrogen peroxide as FA 4. Titration ● Fill the burette with FA 2. ● Pipette 25.0 cm3 of FA 4 into a conical flask. ● Use the measuring cylinder to add 25 cm3 of FA 3 to the conical flask. ● Titrate FA 4 against FA 2 and record your readings in the space below. ● Carry out as many accurate titrations as you think necessary. Results [5]

3 DO NOT WRITE IN THIS MARGIN [Turn over DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2019 DO NOT WRITE IN THIS MARGIN (b) From your titrations, obtain a suitable volume of FA 2 to be used in your calculations. Show clearly how you obtained this volume. 25.0 cm3 of FA 4 required _____________ cm3 of FA 2 for titration [1] (c) Calculations Show your working and give appropriate significant figures in the final answer for each step of your calculations. (i) Calculate the amount of potassium manganate(VII) present in the volume of FA 2 calculated in (b). amount of KMnO4 = [1] (ii) Calculate the amount of hydrogen peroxide present in 25.0 cm3 of FA 4. amount of H2O2 in 25.0 cm3 of FA4 = [1] (iii) Calculate the concentration, in mol dm-3, of H2O2 in FA 4. concentration of H2O2 in FA 4 = [1]

4 DO NOT WRITE IN THIS MARGIN [Turn over DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2019 DO NOT WRITE IN THIS MARGIN (iv) Calculate the concentration, in mol dm-3, of H2O2 in FA 1. concentration of H2O2 in FA 1 = [1] (d) Another experiment was conducted to determine the concentration of hydrogen peroxide. Different volumes of hydrogen peroxide were added to identical 25.0 cm 3 samples of 0.0400 mol dm -3 aqueous iron( II) solut