HCI Prelim Paper 4 Question Paper (final)

HWA CHONG INSTITUTION C2 Preliminary Examination Higher 2 NAME CT GROUP 19S CHEMISTRY Paper 4 Practical Candidates answer on the Question Paper 9729/04 25 August 2020 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 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 2 3 4 Total This document consists of 19 printed pages.

2 © Hwa Chong Institution 2020 9729/04/C2Prelim 2020 [Turn over 1 Determination of the percentage by mass of ethanedioic acid in a solid mixture FA 1 is a solution made by dissolving a solid mixture of ethanedioic acid, H2C2O4, and sodium ethanedioate, Na2C2O4, in water. The percentage by mass of ethanedioic acid in the mixture can be determined by a combination of an acid -base titration ( Titration A) and a redox titration (Titration B). You will carry out Titration A only. FA 2 is 0.0400 mol dm–3 sodium hydroxide. You are also provided with thymol blue indicator. Titration A Ethanedioic acid reacts with sodium hydroxide as follows: H2C2O4(aq) + 2NaOH(aq)  Na2C2O4(aq) + 2H2O(l) (a) 1. Fill a burette with FA 2. 2. Pipette 25.0 cm3 of FA 1 into a conical flask. 3. Add about 10 drops of thymol blue indicator. 4. Add FA 2 from the burette until the end-point has been reached. 5. Carry out as many titrations as you think necessary to obtain consistent results. Record your titration results in a suitable format in the space below. [2] (b) From your titration results, obtain a suitable value for the volume of FA 2 needed to react with the ethanedioic acid in 25.0 cm3 of FA 1. volume of FA 2 needed = ………………………… cm3 [3]

3 © Hwa Chong Institution 2020 9729/04/C2Prelim 2020 [Turn over (c) (i) Calculate the number of moles of sodium hydroxide present in the volume of FA 2 found in (b). number of moles of sodium hydroxide = ………………………… mol [1] (ii) Calculate the number of moles of ethanedioic acid present in 25.0 cm3 of FA 1. number of moles of ethanedioic acid = ………………………… mol [1] Titration B In aqueous solution both ethanedioic acid and sodium ethanedioate releas