2023 TJC H2Chemistry P4 Ans

9729 / TJC Prelims / 2023 DO NOT WRITE IN THIS MARGIN [Turn over TEMASEK JUNIOR COLLEGE 2023 JC2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME ANSWER CIVICS GROUP / CENTRE NUMBER S INDEX NUMBER Chemistry 9729/04 Paper 4 Practical 28 August 2023 2 hours 30 minutes Candidates answer on the Question Paper. READ THESE INSTRUCTIONS FIRST Write your centre number, index number, name and CG on all the work you hand in. Give details of the practical shift and laboratory where appropriate, in the boxes provided. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Answer all questions in the spaces provided on the Question Paper. The use of an approved scientific calculator is expected, where appropriate. You may lose marks if you do not show your working or if you do not use appropriate units. Qualitative Analysis Notes are printed on pages 19 and 20. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 18 printed pages and 2 blank page. For Examiner’s Use 1 2 3 4 Total / 55 Shift Laboratory

2 DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2023 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN Answer all the questions in the spaces provided. 1 In this experiment you are to determine the relative formula mass of an iron(II) salt by titration with potassium manganate(VII). FA 1 is the iron (II) salt. FA 2 is 0.0100 mol dm3 potassium manganate(VII), KMnO4. FA 3 is 1.0 mol dm–3 sulfuric acid, H2SO4. Method (a) Preparing a solution of FA 1 1. Weigh accurately about 4.0 g of FA 1 into the plastic vial labelled FA 1 and record the mass in the space below. 2. Transfer all the weighed FA 1 into a 250 cm3 beaker. 3. Use a measuring cylinder to add approximately 100 cm3 of FA 3 to the beaker. Stir until all the solid has dissolved. 4. Transfer the solution into the 250 cm3 volumetric (graduated) flask labelled FA 4. 5. Wash out the beaker thoroughly using distilled water and add the washings to the volumetric flask. Make the solution up to the mark using distilled water. 6. Shake the flask thoroughly to mix the solution before using it for your titrations. Label this solution of the iron(II) salt as FA 4. Mass of plastic vial/g 6.01 Mass of plastic vial and FA 1/g 9.91 Mass of plastic vial and residue/g 6.01 Mass of FA 1 used/g 3.90 [2] [1] Table with correct headings and units [1] All readings to 2 or 3 d.p (b) Titration of FA 4 against FA 2 1. Fill the burette with FA 2. Retain the burette containing FA 2 for Q2. 2. Pipette 25.0 cm3 of FA 4 into a conical flask. 3. Use a measuring cylinder to add 20 cm3 of FA 3 to the flask. 4. Titrate FA 4 with FA 2 until the solution changes to a permanent pink colour. 5. Record your titration results, to an appropriate level of precision, in th e space provided below. 6. Repeat steps 2 to 5 until consistent results are obtained. (i) Titration results

3 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2023 DO NOT WRITE IN THIS MARGIN [Turn over Titration No. 1 2 Final burette reading / cm3 22.10 43.45 Initial burette reading / cm3 0.70 22.10 Volume FA 2 used / cm3 21.40 21.35   [1] Table with correct headings and units [1] All readings to 2 d.p [2] (ii) From your accurate titration results, obtain a suitable value to be used in your calculations. Show clearly how you have obtained this value. [4] Average volume of FA 2 used = (21.40 + 21.35)/2 cm3 = 21.38 cm3 [1] Show correct working using consistent readings Accuracy: [3m] supervisor reading ± 0.03 cm3 g-1 [2m] supervisor reading ± 0.06 cm3 g-1 [1m] supervisor reading ≤ 0.10 cm3 g-1 (c) Calculations (i) Calculate the number of moles of potassium manganate(VII) present in the volume of FA 2 calculated in (b)(ii). [1] Amount of MnO4  = 21.38/1000 x 0.01 mol = 2.14 x 10-4 mol [1] (ii) The half-equation for the reduction of a manganate(VII) ion is: MnO4  + 8H+ + 5e Mn2+ + 4H2O Write the complete balanced ionic equation for the oxidation of iron(II) ion to iron(III) by manganate(VII) ions. [1] MnO4  + 8H+ + 5Fe2+  Mn2+ + 5Fe3+ 4 H2O (iii) Calculate the number of moles of iron(II) ions present in 25.0 cm3of solution FA 4. [1] MnO4   5Fe2+ Amount of Fe2+ in 25.0 cm3 = 2.14 x 10-4 x 5 mol = 1.07 x 10-3 mol [1]

4 DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2023 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN (iv) Calculate the number of moles of iron(II) ions present in 250 cm3 of solution FA 4. [1] Amount of Fe2+ in 250 cm3 = 1.07 x 10-3 x 10 mol = 1.07 x 10-2 mol [1] (v) Calculate the relative formula mass of the iron(II) salt. [3] Amount of salt = 1.07 x 10-2 mol Mass of salt weighed = 3.90 g Mr = 3.90/1.07 x 10-2 = 364.5 [1] [1] Shows working in all calculations. All calculations must be relevant although they may not be complete or correct. Any calculation not attempted loses this mark. [1] Shows appropriate significant figures (3 or 4 sf) and units in all final answers. Any calculation not attempted loses this mark. (d) A student conducted the above experiments and obtained an average titre value of 19.30 cm3. The errors (uncertainties) associated with each reading using a graduated flask, pipette and burette are 0.15 cm3, 0.10 cm3 and 0.05 cm3 respectively. Calculate the maximum total percentage error (uncertainty) of this mean titre volume. [1] Maximum % error =  (0.15/250 + 0.10/25.0 + 2x0.05/19.30) x 100 =  (6 x 10-4 + 4 x 10-3 + 5.18 x 10-3) x 100 = 0.978 [1] [Total: 16]

5 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2023 DO NOT WRITE IN THIS MARGIN [Turn over 2 Glucose, C6H12O6, is a sugar that can act as a reducing agent. You will investigate how an increase in temperature affects the rate of the redox reaction between gl ucose and acidified potassium manganate(VII). FA 2 is 0.010 mol dm–3 potassium manganate(VII), KMnO4. FA 3 is 1.0 mol dm–3 sulfuric acid, H2SO4. FA 5 is an aqueous solution containing 32.8 g dm–3 glucose, C6H12O6. distilled water You will measure the time it takes for the purple colour to disappear. Your table of results on page 8 should include the rate of reaction for each experiment. (a) Method Experiment 1 1. Add 10.00 cm 3 of FA 2 from the burette (in question 1) into the 250 cm3 beaker. 2. Use the 100 cm 3 measuring cylinder to transfer 50.0 cm 3 of FA 3 into the beaker containing FA 2. 3. Use the same measuring cylinder to transfer 50.0 cm 3 of distilled water into the same beaker. 4. Place the beaker on the tripod and heat its contents to between 65 °C and 70 °C. 5. While the solution in the beaker is heating pour 25.0 cm 3 of FA 5 into the 25 cm 3 measuring cylinder. 6. When the temperature of the contents of the beaker has reached bet ween 65 °C and 70 °C, turn off the Bunsen burner and carefully place the hot beaker onto the white tile. 7. Record the initial temperature, T i, of the solution in the beaker. 8. Add the 25.0 cm 3 of FA 5 and immediately start timing. 9. Stir the contents of the beaker once and stop timing as soon as the sol ution turns colourless. Record the time to the nearest second. 10. Record the final temperature, T f, of the solution as soon as it is colourless. 11. Calculate and record the average temperature, T av