VJC 2020 H2 Chem Prelim P4_Ans

1  VJC 2020 H2 PRELIMINARY EXAMINATION [Turn over This document consists of 17 printed pages and 1 blank page. CANDIDATE NAME CT GROUP VICTORIA JUNIOR COLLEGE PRELIMINARY EXAMINATION Higher 2 ……………………………………………….………….. …………………………….. CHEMISTRY 9729/04 Paper 4 Practical Candidates answer on the Question Paper. 31 Aug 2020 2 hours 30 minutes Additional Materials: As listed in the instructions below READ THESE INSTRUCTIONS FIRST Write your name and CT group 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 a 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 14 and 15. 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 / 12 2 / 13 3 / 17 4 / 13 Total / 55

2  VJC 2020 H2 PRELIMINARY EXAMINATION Answer all the questions in the spaces provided. 1 X is a solid sample of sodium ethanedioate, Na2C2O4 and ethanedioic acid, H2C2O4, a weak acid. FA 1 is prepared by dissolving 2.00 g of X in a 250 cm3 volumetric flask and making up to the mark with deionised water. FA 2 is 0.0100 mol dm3 sodium hydroxide, NaOH(aq). FA 3 is 0.0200 mol dm3 potassium manganate(VII), KMnO4(aq). Titration of FA1 against FA2 (a) 1. Fill a burette with FA 2. 2. Pipette 25.0 cm3 of FA 1 into a conical flask. 3. Add 2−3 drops of thymolphthalein indicator to the conical flask. 4. Titrate FA1 against FA 2 until a distinct colour change is observed. 5. Carry out as many titrations as you deem necessary to obtain consistent results. 6. Record in an appropriate form all of your burette readings and the volume of FA 2 added in each titration. Final burette reading / cm3 20.50 41.60 Initial burette reading / cm3 0.00 21.00 Volume of FA 2 used / cm3 20.50 20.60 [4] (b) (i) From your titration results, obtain a suitable volume of FA 2 to be used in your calculations. Show clearly how you obtained this volume. Average volume of FA 2 used = (20.50 + 20.60) ÷ 2 = 20.55 cm3 25.0 cm3 of FA 1 required ………………… cm3 of FA 1. [1] The equation for the reaction between sodium hydroxide and ethanedioic acid in this experiment is shown below: H2C2O4 + 2NaOH  Na2C2O4 + 2H2O