NYJC Prelim 9729_P4_Answers

1 [Type here] H2 Chemistry 9729/04 NYJC J2/18 PX [Turn over NANYANG JUNIOR COLLEGE JC2 PRACTICAL PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME Mark Scheme CLASS 1 7 REG NO. TUTOR CHEMISTRY 9729/04 Paper 4 Practical 28 August 2018 2 hour 30 minutes Candidates answer on the Question Paper Additional Materials: As listed in the Confidential Instructions 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. Shift 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 22 and 23. Laboratory 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. For Examiner’s Use 1 / 28 2 / 11 3 /16 Total /55 This document consists of 23 printed pages and 1 blank page.

2 [Type here] H2 Chemistry 9729/04 NYJC J2/18 PX [Turn over Answer all the questions in the spaces provided. 1 To determine the concentrations of aqueous sodium hydroxide and aqueous ethanedioic acid and hence the percentage by mass of sodium ethanedioate in a mixture of sodium ethanedioate and ethanedioic acid. You are provided with the following reagents. • FB 1 is a mixture of approximately 0.01 mol dm −3 aqueous sodium ethanedioate, C2O4Na2, and approximately 0.1 mol dm−3 ethanedioic acid, C2O4H2 • FB 2 is a dilute solution of sodium hydroxide, NaOH • FB 3 is 0.0755 mol dm−3 aqueous sodium carbonate • thymolphthalein indicator Both sodium hydroxide and sodium carbonate are bases which will neutralise ethanedioic acid as shown in reactions 1 and 2. 2NaOH + C2O4H2 → C2O4Na2 + 2H2O reaction 1 Na2CO3 + C2O4H2 → C2O4Na2 + CO2 + H2O reaction 2 In this experiment, you will add different volumes of FB 3 to identical samples of the mixture of aqueous sodium ethanedioate, C 2O4Na2, and ethanedioic acid, C 2O4H2, FB 1. You will then complete the neutralisation of C 2O4H2 in each mixture by titration with dilute sodium hydroxide, FB 2. Each titration is to be performed once only, so great care should be taken that you do not overshoot the end-points. Graphical analysis of your results will enable you to determine the concentrations of the ethanedioic acid in the mixture of aqueous C 2O4Na2, and C2O4H2 and of the sodium hydroxide. Read through the whole method of conducting the experiment before starting any practical work. The experiment (a) Titrations