2019 NYJC Prelim P4 QP

[Turn Over NANYANG JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME TUTOR’S NAME CLASS CHEMISTRY 9729/04 Paper 4 Practical 19 August 2019 2 hours 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, 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 18 and 19. 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 / 28 2 / 11 3 / 16 Total / 55 This document consists of 19 printed pages.

2 H2 Chemistry 9729/04 NYJC J2/2019 PRELIM 1 Determination of the percentage by mass of ethanedioic acid FA 1 is a solution made by dissolving an unknown mass of a mixture of ethanedioic acid, H2C2O4, and sodium ethanedioate, Na2C2O4. In aqueous solution, both ethanedioic acid and sodium ethanedioate release all their ethanedioate ions, C2O42ꟷ. These ions react with manganate(VII) ions as shown. 2MnO4ꟷ(aq) + 16H+(aq) + 5C2O42ꟷ(aq)  10CO2(g) + 2Mn2+(aq) + 8H2O(l) You will carry out titrations to find the percentage by mass of ethanedioic acid in the mixture. FA 2 is 0.0200 mol dm–3 potassium manganate(VII), KMnO4. FA 3 is 1.00 mol dm–3 sulfuric acid, H2SO4. (a) (i) Titration of FA 1 against FA 2 1. Fill a burette with FA 2. 2. Pipette 25.0 cm3 of FA 1 into a conical flask. 3. Use the measuring cylinder to add 30.0 cm3 of FA 3 to the same conical flask. 4. Place the conical flask on the tripod and gauze and heat until the temperature of the solution is approximately 70 °C. 5. Carefully remove the flask from the tripod. Add a few drops of FA 2 from the burette and swirl the mixture until it turns colourless. Note: If the reaction mixture does not decolourise or turns brown, reheat it to about 70 °C. Swirl the mixture till it decolourises. If the brown colour remains, discard the contents of the flask and begin a new titration. 6. Continue the titration until a permanent pale pink is obtained. 7. Record your titration results, to an appropriate level of precision, in the space provided on page 3. 8. Repeat points 2 to 7 until consistent results are obtained.

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