Copy of CHS 2024_S4_OP_Prelim Paper 3

Name: Index Number: Class: CATHOLIC HIGH SCHOOL Preliminary Examination Secondary 4 (O-Level Programme) End-of-Year Examination Year 4 (Integrated Programme) CHEMISTRY 6092/03 Paper 3 Practical 2 August 2024 Candidates answer on the Question Paper 1 hour 50 minutes Additional Materials: - READ THESE INSTRUCTIONS FIRST Write your name, index number 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 page 16. 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 / 18 2 / 11 3 / 7 4 / 4 Total / 40 This document consists of 14 printed pages and 2 blank pages.

2 1 Sodium carbonate can occur as a hydrated solid with the formula Na2CO3∙nH2O. In these crystals, one formula unit of sodium carbonate, Na2CO3, combines with n molecules of water. There are two methods to determine the value of n. Each method involves sodium carbonate reacting with excess hydrochloric acid to release carbon dioxide. Na2CO3∙nH2O(s) + 2HCl(aq) → 2NaCl(aq) + CO2(g) + (n + 1)H2O(l) You will carry out one method each in Experiment 1 and Experiment 2. You will only determine the value of n in hydrated sodium carbonate, Na2CO3∙nH2O, in Experiment 1. Read all the instructions below carefully before starting the experiments in Question 1. Instructions (a) (i) Experiment 1 You will perform a titration to measure the volume of hydrochloric acid that neutralises an aqueous solution of hydrated sodium carbonate, Na2CO3∙nH2O. P is 0.100 mol/dm3 hydrochloric acid. Q is an aqueous so lution containing 14.3 g /dm3 of hydrated sodium carbonate, Na2CO3∙nH2O. R is bromophenol blue indicator. Method Fill the burette with P. Use the pipette to transfer 25.0 cm3 of Q into a conical flask. Add a few drops of R into the flask. Add P from the burette, swirling the flask constantly. At the end-point, one drop of P produces a yellow colour that does not disappear on swirling. Record your titration results in the space provided , repeating the titration as many times as you consider necessary to achieve consistent results. Results [5]

3 [Turn over (ii) Use your titration results to obtain the average volume of P used. Show clearly how you obtained this vol