EJC Prelim H2 Chemistry Paper 4 QP

© EJC 9729/04/J2Prelim/25 [Turn Over EUNOIA JUNIOR COLLEGE JC2 Preliminary Examination 2025 General Certificate of Education Advanced Level Higher 2 CANDIDATE NAME CIVICS GROUP 2 4 – INDEX NUMBER CHEMISTRY Paper 4 Practical 9729/04 21 August 2025 2 hour 30 minutes Candidates answer on the Question Paper. Additional Materials: As listed in the Confidental Instructions READ THESE INSTRUCTIONS FIRST Write your name, civics group and registration number on 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 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. 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. Shift Laboratory For Examiner’s Use 1 / 5 2 / 11 3 / 17 4 / 9 5 / 13 Total / 55 This document consists of 20 printed pages.

2 © EJC 9729/04/J2Prelim/25 Answer all the questions in the spaces provided. 1 Investigation of redox reactions involving D-glucose D-Glucose is a sugar with molecular formula C6H12O6, which can react directly or indirectly with potassium manganate(VII), KMnO4. (a) FA 1 is a solution of potassium manganate(VII), KMnO4. FA 2 is a 1.0 mol dm−3 sulfuric acid solution, H2SO4. You are also provided with a solution of D-glucose and bench reagents. Perform the tests described in Table 1.1 and record your observations in the table. Table 1.1 test observations (i) Add 1 cm depth of FA 1 to a test -tube. Add an equal volume of aqueous sodium hydroxide. Add 1 drop of glucose solution and shake thoroughly. Allow to stand for 10 minutes, with occasional shaking. Continue with the remaining parts of Question 1. (ii) Add 1 cm depth of FA 1 to a boiling tube. Add 2 cm depth of FA 2. Add 1 cm depth of glucose solution and warm gently. Shake well to mix. [2]

3 © EJC 9729/04/J2Prelim/25 [Turn Over (b) Manganese species exist in ions of different oxidation states and colours. Suggest the identity of the final manganese-containing species in (a)(i) and in (a)(ii). final manganese-containing species in (a)(i) ................................ ................................ final manganese-containing species in (a)(ii) ................................ ............................... [1] (c) In (a)(i), D-glucose, C6H12O6, reacts with KMnO 4 in alkaline medium to give D-gluconate, C6H11O – 7. (i) Name the type of reaction that D-glucose undergoes in (a). ................................ ................................ ................................ ........................ [1] (ii) Draw the structure of the D-gluconate ion. [1] [Total: 5]

4 © EJC 9729/04/J2Prelim/25 2 Determination of mass of D-glucose in a sample The Bertrand method is a classical redox titration technique used to determine the amount of reducing sugars, such as D-glucose. In this method, a sample of D-glucose, C6H12O6, is reacted with excess alkaline copper(II) solution, Cu2⁺, to form insoluble copper(I) oxide, Cu2O. equation 1 C6H12O6 + 2Cu2+ + 5OH− → C6H11O – 7 + Cu2O + 3H2O The Cu₂O is filtered and dissolved in 100 cm3 acidic iron(III) solution, Fe3+. equation 2 Cu2O + 2Fe3+ + 2H+ → 2Cu2+ + 2Fe2+ + H2O The resulting solution is then diluted to 1 dm3. The diluted solution is labelled FA 3. The amount of Fe2⁺ present in FA 3 is then determined by titration with potassium manganate(VII), KMnO4, in acidic medium. The end-point of the titration occurs when the presence of unreacted MnO – 4 causes the colour of the solution to become pale pink. equation 3 5Fe2+ + MnO – 4 + 8H+ → 5Fe3+ + Mn2+ + 4H2O You are to determine the amount of Fe 2⁺ present in FA 3 and hence determine the mass of D-glucose in the sample. FA 1 is 0.0200 mol dm−3 potassium manganate(VII), KMnO4. FA 2 is 1.0 mol dm−3 sulfuric acid solution, H2SO4. (a) (i) Procedure 1. Fill the burette with FA 1. 2. Pipette 25.0 cm3 of FA 3 into a clean 250 cm3 conical flask. 3. Use a measuring cylinder to add 10.0 cm3 of FA 2 to the conical flask. 4. Run FA 1 from the burette into the conical flask. The end -point is reached when the first permanent trace of pale pink colour is seen. 5. Record your titration results, to an appropriate level of precision, in Table 2.1. 6. Repeat points 2 to 5 until consistent titre values are obtained. Table 2.1 final burette reading / cm3 initial burette reading / cm3 volume of FA 1 used / cm3 [2]

5 © EJC 9729/04/J2Prelim/25 [Turn Over (ii) From your titration results, obtain a suitable volume of FA 1 to be used in your calculations. Show clearly how you obtained this volume. volume of FA 1 = ................................ ............. cm3 [3] (b) (i) Calculate the amount of Fe2+ in 1 dm3 of FA 3. amount of Fe2+ in 1 dm3 of FA 3 = ................................ ........................ [3] (ii) Calculate the mass of D-glucose, C6H12O6, in the sample. [Ar: H, 1.0; C, 12.0; O, 16.0] mass of glucose in sample = ................................ .................... [2] (c) A student repeated the procedure in (a) and obtained an average titre value of 19.50 cm3. The errors (uncertainties) associated with each reading using pipette and burette are 0.10 cm3 and 0.05 cm3 respectively. Calculate the maximum total percentage error (uncertainty) of this average titre volume. [1] [Total: 11]

6 © EJC 9729/04/J2Prelim/25 3 Determination of the enthalpy change when citric acid reacts with sodium hydrogencarbonate Citric acid, C6H8O7, is found in citrus fruit such as lemons and limes. It is a triprotic (tribasic) acid – one mole of citric acid reacts with three moles of sodium hydrogencarbonate. equation 4 C6H8O7(aq) + 3NaHCO3(s) → C6H5O7Na3(aq) + 3CO2(g) + 3H2O(l) H1 FA 4 is 0.080 mol dm–3 citric acid, C6H8O7. FA 5 is solid sodium hydrogencarbonate, NaHCO3. (a) Calculate the minimum mass of sodium hydrogencarbonate that will react completely with the citric acid in 50.0 cm3 of FA 4. [Ar: Na, 23.0; H, 1.0; C, 12.0; O, 16.0] minimum mass of NaHCO3 = ................................ ................... [1] (b) Determination of the molar enthalpy change of reaction, H1 In this experiment, you will measure the temperature of the contents of a polystyrene cup at time d intervals, both before and after an excess of FA 5 is added. You will analyse your results graphically to obtain an accurate value for the temperature change caused by the reaction. You will use this value to calculate the heat change, q, for the experiment and hence determine a value for the molar enthalpy change of the reaction, H1. In the space provided on page 7, prepare a table in which to record for your experiment: • all values of temperature, T, to an appropriate level of precision • all values of time, t, recorded to the nearest 0.5 min. It is important that you measure each temperature at the specified time.

7 © EJC 9729/04/J2Prelim/25 [Turn Over Procedure 1. Measure 50.0 cm3 of FA 4 using a 50.0 cm3 measuring cylinder. 2. Place one polystyrene cup inside a glass beaker. 3. Transfer 50.00 cm3 of FA 4 into the polystyrene cup. 4. Carefully stir the FA 4 in the polystyrene cup with the thermometer. Read and record the temperature, T.