2020 EJC JC2 Prelim H2 Chemistry Paper 4 Suggested Solutions

© EJC 9729/04/J2PE/20 [Turn Over EUNOIA JUNIOR COLLEGE JC2 Preliminary Examination 2020 General Certificate of Education Advanced Level Higher 2 CANDIDATE NAME CIVICS GROUP 1 9 – INDEX NUMBER CHEMISTRY Paper 4 Practical 9729/04 01 September 2020 2 hours 30 minutes Candidates answer on the Question Paper. Additional Materials: As listed in the Confidental Instructions READ THESE INSTRUCTIONS FIRST Write your name, civics group and registration number on 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 paper clips, highlighters, 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 19 and 20. 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 / 34 3 / 9 Total / 55 This document consists of 17 printed pages and 3 blank pages.

2 © EJC 9729/04/J2PE/20 For Examiner’s Use Answer all the questions in the spaces provided. 1 Standardisation of KMnO4 FA 1 is approximately 0.02 mol dm–3 potassium manganate(VII), KMnO4 FA 2 is 0.200 mol dm–3 potassium ethanedioate, K2C2O4 FA 3 is 1.0 mol dm–3 sulfuric acid, H2SO4 KMnO4 is not a primary standard as it cannot be obtained in a sufficiently pure state to allow its concentration to be determined by preparing a solution from a known mass of solid KMnO4. However, it can be standardised by using potassium ethanedioate, K2C2O4. Acidified MnO4– ions oxidises C2O42– ions as shown in equation 1. The Mn2+ ions produced in equation 1 act as a catalyst for the reaction. This is an example of ‘autocatalysis’. equation 1 2MnO4–(aq) + 5C2O42–(aq) + 16H+(aq)  2Mn2+(aq) + 10CO2(g) + 8H2O(l) In this question, you will perform a titration. The data from this titration will be used to determine the concentration of MnO4– ions in FA 1. (a) Titration of FA 2 against FA 1 In this titration, FA 1 is run from the burette into the conical flask containing FA 2 and FA 3. Initially, the colour of the FA 1 will take some time to disappear. After some FA 1 has been added, sufficient Mn 2+(aq) ions will be present to allow the reaction to occur faster. The end-point is reached when a permanent pale pink colour is obtained. (i) 1. Fill the burette labelled FA 1 with FA 1. 2. Using a pipette, transfer 10.0 cm3 of FA 2 into the conical flask. 3. Using an appropriate measuring cylinder, transfer 50.0 cm 3 of FA 3 to the