2021 HCI Prelim Paper 4 Questions

HWA CHONG INSTITUTION C2 Preliminary Examination Higher 2 NAME CT GROUP 20S CHEMISTRY Paper 4 Practical Candidates answer on the Question Paper 9729/04 18 August 2021 2 hours 30 minutes READ THESE INSTRUCTIONS FIRST Write your name and class 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 17 and 18. 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 2 3 4 Total This document consists of 18 printed pages.

2 © HCI 9729/04/Prelim2021 [Turn over 1 Determination of the values for the enthalpy changes associated with several chemical reactions and concentration of aqueous sodium hydroxide FA 1 is aqueous sodium hydroxide, NaOH FA 2 is 1.00 mol dm–3 sulfuric acid, H2SO4 FA 3 is citric acid crystals, C3H4(OH)(CO2H)3.H2O Sodium hydroxide and sulfuric acid react according to equation 1. The enthalpy change for the reaction is 'H1. equation 1 2NaOH(aq) + H2SO4(aq) o Na2SO4(aq) + 2H2O(l) 'H1 Sodium hydroxide and citric acid crystals react according to equation 2. The enthalpy change for the reaction is 'H2. equation 2 3NaOH(aq) + C3H4(OH)(CO2H)3.H2O(s) o C3H4(OH)(CO2Na)3(aq) + 4H2O(l) 'H2 In this question, you will perform experiments to determine the values for 'H1 and 'H2. You will use your values of 'H1 and 'H2 to calculate a value for the enthalpy change shown in equation 3. equation 3 C3H4(OH)(CO2H)3.H2O(s) o C3H4(OH)(CO2)3(aq) + 3H+(aq) + H2O(l) 'H3 In 1(c), you will use data provided to determine the concentration of sodium hydroxide in FA 1. (a) You will follow the instructions to perform experiments 1 and 2. Record your results in the space provided on page 3. Experiment 1 1. Using a measuring cylinder, transfer 50.0 cm3 of FA 1 into a Styrofoam cup. Place this cup inside a second Styrofoam cup, which is placed in a 250 cm3 glass beaker. 2. Stir and measure the temperature of this FA 1, TFA1. 3. Using another measuring cylinder, measure 20.0 cm3 of FA 2. 4. Stir and measure the temperature of this FA 2, TFA2. 5. Add the FA 2 from the measuring cylinder to the FA 1 in the Styrofoam cup. 6. Using the thermometer, stir the mixture continuously until it reaches its maximum temperature. Record this temperature, Tmax. Experiment 2 1. Weigh the capped bottle containing FA 3. 2