2021 NYJC Prelim 9729 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 23 August 2021 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 16 and 17. 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 / 13 2 / 15 3 / 9 4 / 18 Total / 55 This document consists of 17 printed pages..

2 H2 Chemistry 9729/04 NYJC J2/2021 PRELIM. 1 Determination of the concentration of hydrogen peroxide FA 1 is a solution of hydrogen peroxide, H2O2, of unknown concentration. In this experiment, you will react hydrogen peroxide with excess potassium iodide solution in an acidic condition to produce iodine as shown in equation 1. H2O2 + 2I– + 2H+ J I2 + 2H2O equation 1 The iodine produced is then titrated with a standard solution of sodium thiosulfate as shown in equation 2. I2 + 2S2O32– J 2I– + S4O62– equation 2 FA 2 is 0.50 mol dm–3 sulfuric acid, H2SO4. FA 3 is 0.500 mol dm–3 potassium iodide, KI. FA 4 is 0.200 mol dm–3 sodium thiosulfate, Na2S2O3. Starch solution. You will determine the concentration of hydrogen peroxide by first reacting a fixed amount of hydrogen peroxide with excess potassium iodide and subsequently titrating the iodine produced with sodium thiosulfate. (a) In a preliminary experiment, a student pipetted 25.0 cm3 of FA 1 into a conical flask containing FA 2 and FA 3. The resulting solution was titrated against FA 4 from a burette and a very large titre value was obtained. He deduced the concentration of FA 1 was too high and required dilution. (i) Procedure 1. Using the burette labelled FA 1, run between 24.00 cm3 and 24.50 cm3 of FA 1 into a clean 250 cm3 graduated flask. Set aside this burette labelled FA 1 and its contents for Question 2. 2. Record your burette readings to an appropriate level of precision in the space provided below. 3. Top up the flask to mark with deionised water. Stopper the flask and mix the contents thoroug