2022 RVHS JC2 H2 CM Prelim P4 (QP)

RIVER VALLEY HIGH SCHOOL JC 2 PRELIMINARY EXAMINATION H2 CHEMISTRY 9729 Paper 4 19 AUGUST 2022 2 HOURS 30 MINUTES NAME CLASS 21J ( ) INDEX NO. INSTRUCTIONS TO CANDIDATES DO NOT OPEN THIS BOOKLET UNTIL YOU ARE TOLD TO DO SO. Read these notes carefully. Write your name, class and index number in the spaces at the top of this page. Give details of the practical shift and laboratory where appropriate, in the boxes provided. Write in dark blue or black pen. You may use a 2B pencil for any diagram or graph. Do not use staples, paper clips, highlighters, 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. Shift Laboratory For Examiner’s Use s.f. Units Total 55 _______________________________________________________________________________ This Question Paper consists of 19 printed pages and 1 blank page.

River Valley High School Pg 2 of 20 JC 2 H2 Chemistry 9729 2022 Preliminary Examination Paper 4 Answer all the questions in the spaces provided. 1 Investigation of the oxidising ability of substances FA 1 is an aqueous solution of iron(II) sulfate. FA 2 is made by dissolving 0.750 g of KMnO 4 in deionised water and made up to 250 cm3 in a volumetric flask. FA 3 is 0.500 mol dm−3 compound A. FA 4 is 1 mol dm−3 sulfuric acid. You will perform tests to: • investigate the oxidising ability of three substances • carry out a titration to determine the concentration of iron(II) sulfate in FA 1. (a) (i) Carry out the following tests. Carefully record your observations in Table 1.1. The volumes given below are approximate and should be estimated rather than measured. In this section, there is only one gas evolved. You only need to carry out the identification test and identify the gas once. Table 1.1 Test Observations 1 To a 1 cm depth of FA 1 in a test-tube, add 1 cm depth of FA 4 , then gradually add FA 2 till 1 drop in excess. 2 To a 1 cm depth of FA 3 in a test-tube, add 1 cm depth of FA 2. 3 To a 1 cm depth of FA 1 in a test-tube, add about 1 cm depth of FA 4, followed by 1 cm depth of FA 3. To a portion of resulting solution, add aqueous sodium hydroxide till excess. 1 2 3

River Valley High School Pg 3 of 20 JC 2 H2 Chemistry 9729 2022 Preliminary Examination Paper 4 (ii) Explain the chemistry involved for all the observations in Test 1. 4 (iii) Write two equations to show the changes to Fe2+ ions in Test 3. 5 6 (iv) Using the results in Test 3, state the stronger oxidising agent. 7

River Valley High School Pg 4 of 20 JC 2 H2 Chemistry 9729 2022 Preliminary Examination Paper 4 (b) (i) Titration of FA 1 against FA 2 1. Fill a burette with FA 2. 2. Use the pipette to transfer 25.0 cm3 of FA 1 into a 250 cm3 conical flask. 3. Use a measuring cylinder to add 20.0 cm 3 of FA 4 into the same conical flask. 4. Titrate the mixture in the conical flask until the end-point is reached. 5. Record your titration results, to an appropriate level of precision, in the space provided below. 6. Repeat points 2 to 5 until consistent results are obtained. Titration results 8 9 10 11 12 Difference in titres (ii) From y our titrations, obtain a suitable volume of FA 2 to be used in your calculations. Show clearly how you obtained this volume. volume of FA 2 used = ………………………… 13

River Valley High School Pg 5 of 20 JC 2 H2 Chemistry 9729 2022 Preliminary Examination Paper 4 (c) (i) Calculate the amount of MnO4− used in the titration. [Ar: K, 39.1; Mn, 54.9; O,16.0] amount of MnO4− = ..………………… 14 (ii) Given that 1 mole of MnO 4− reacts with 5 moles of Fe 2+, calculate the molar concentration of iron(II) sulfate in FA 1. molar concentration of iron(II) sulfate = ..………………… 15 (d) A student plans to titrate 25.0 cm 3 of aqueous solution containing iron( II) chloride with FA 2 as the titrant. This iron( II) chloride solution has similar molar concentration as iron(II) sulfate in FA 1. Without changing the identity of the chemicals used, s uggest a modification to improve the experiment. Explain your answer. You are not required to show any calculations. 16

River Valley High School Pg 6 of 20 JC 2 H2 Chemistry 9729 2022 Preliminary Examination Paper 4 (e) In a series of titrations, a student pipette d 25.0 cm3 of FA 1 into the conical flask and added varying volumes of FA 3 from the burette to form a mixture. This mixture was titrated with FA 2 till end-point was reached. The results are shown below in Table 1.2. Table 1.2 experiment 1 2 3 4 5 volume of FA 3 added /cm3 5.00 10.00 15.00 20.00 25.00 volume of FA 2 used /cm3 15.45 10.55 5.70 1.25 3.45 (i) Explain why the volumes of FA 2 obtained decrease as VFA3 increases from 5.00 cm3 to 20.00 cm3. 17 (ii) Considering the chemistry involved, deduce whether the volume of FA 2 used in experiment 5 is an anomaly. Explain your answer. 18 19 (iii) Calculate the highest percentage uncertainty in the volume of FA 2 used as shown in Table 1.2. percentage uncertainty = ..………………… 20 [Total: 20]

River Valley High School Pg 7 of 20 JC 2 H2 Chemistry 9729 2022 Preliminary Examination Paper 4 2 Investigation of the kinetics of the reaction between iron(III) ions and iodide ions In acidic solutions, iron( III) ions are reduced by iodide ions to form iron( II) ions. The iodide ions are oxidised to iodine. 2Fe3+(aq) + 2I–(aq) → 2Fe2+(aq) + I2(aq) The rate of this reaction can be investigated by using starch indicator, which turns blue-black in the presence of iodine. Sodium thiosulfate is added to the reaction mixture to react with iodine as it is formed. The blue-black colour is seen when all the thiosulfate has reacted. I2(aq) + 2S2O32–(aq) → 2I–(aq) + S4O62–(aq) You will perform a series of f our experiments to investigate how the rate of reaction is affected by changing the concentration of the iodide ions. For each experiment, you will note the volume of FA 5 added, VFA 5, the volume of water added, VH2O, and the time taken, t, for the reaction mixture to turn blue-black. In this series of experiments, the rate equation for the reaction can be simplified to rate = k' [I–]m , where m is the rate order with respect to I– and k’ is k[Fe3+]. The simplified rate equation can be further manipulated to derive the following relationship: lg( 3600 reaction time ) = m  lg(VFA 5) + constant FA 5 is 0.0500 mol dm–3 potassium iodide, KI. FA 6 is 0.0500 mol dm–3 iron(III) chloride, FeCl3. FA 7 is 0.0050 mol dm–3 sodium thiosulfate, Na2S2O3. FA 8 is starch indicator. (a) In the space provided on page 8, p repare a table in which to record for your experiment: • all values of VFA 5 and VH2O to an appropriate level of precision • all values of t • all calculated values of lg(VFA 5) and lg(rate) to three significant figures. Experiment 1 1. Use a 25.00 cm 3 measuring cylin der to place 20.00 cm3 of FA 5 in a 100 cm3 beaker. 2. Use appropriate measuring cylin ders to add the following to the same beaker. • 20.0 cm3 of FA 7 • 10.0 cm3 of FA 8 3. Use an appropriate measuring cylinder to measure 10.0 cm3 of FA 6. 4. Add this FA 6 to the same 100 cm3 beaker and start timing immediately. 5. Stir the mixture and place the beaker on a white tile. 6. Stop timing as soon as the solution turns blue-black. 7. Record this reaction time to the nearest 0.1 second. 8. Wash the