2022 JC2 H2 Chem Prelim P4 Answers for Review

[Turn over 9729/04/CJC JC2 Preliminary Examinations 2022 CANDIDATE NAME CLASS 2T CHEMISTRY 9729/04 Paper 4 Practical 23 August 2022 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 in the boxes above. 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 20 and 21. 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. This document consists of 24 printed pages and 0 blank page. Catholic Junior College JC2 Preliminary Examinations Higher 2 Shift Laboratory For Examiner’s Use 1 / 15 2 / 13 3 / 27 Total / 55 ANSWERS for review

2 [Turn over 9729/04/CJC JC2 Preliminary Examinations 2022 Answer all the questions in the spaces provided. 1 Determination of the Mr of a hydrated ethanedioate salt , using acidified potassium manganate(VII) by titration Calcium ethanedioate is the major component of the most common type of human kidney stones. It is one of a series of salts formed from ethanedioic acid, H 2C2O4. Another of these salts can be represented by the formula X2C2O4H2O, where X is a Group 1 metal. Solution Q contains 64.5 g dm–3 of X2C2O4H2O in deionised water. You are not provided with Q. FA 1 is a diluted solution of Q, in which 35.70 cm 3 of Q was made up to 250 cm 3 with deionised water in a graduated flask. FA 2 is 0.0200 mol dm–3 potassium manganate(VII), KMnO4. FA 3 is 1.00 mol dm–3 sulfuric acid, H2SO4. In this question, you will perform a titration. The data from this titration will be used to determine:  the concentration of C2O42– ions in Q.  the Mr of X2C2O4H2O, and hence the identity of the metal X. (a) Titration of FA 1 against FA 2 In this titration, FA 2 is run from a burette into the conical flask containing FA 1 and FA 3. Initially, the colour of the FA 2 will take some time to disappear. After some FA 2 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 with FA 2. 2. Using a pipette, transfer 25.0 cm3 of FA 1 into the conical flask. 3. Using an appropriate measuring cylinder, tran