2019 NJC Prelim P4 ANS

NJC SH2 Preliminary Examination 9729/04/19 [Turn over NATIONAL JUNIOR COLLEGE SH 2 Year – End Practical Examination Higher 2 CANDIDATE NAME SUBJECT CLASS REGISTRATION NUMBER CHEMISTRY Paper 4 Practical Candidate answer on the Question paper. 9729/04 Tuesday 20 August 2019 2 hours 30 minutes READ THE INSTRUCTIONS FIRST Write your identification number and name. Circle 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, 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, w here 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, submit the question paper. The number of marks is g iven in brackets [ ] at the end of each question or part question. Shift 1 2 3 Laboratory CM41 CM42 CM43 CM44 PH31 PH32 PH33 BI23 BI24 For Examiner’s Use 1 / 12 2 / 21 3 / 14 4 / 8 Total / 55 This document consists of 19 printed pages and 1 blank page.

2 NJC SH2 Preliminary Examination 9729/04/19 1 Determination of the solubility product of calcium iodate(V) When solid calcium iodate( V) is added to water to form a saturated solution, an equilibrium between the undissolved salt and its aqueous ions is established. Ca(IO3)2 (s) Ca2+ (aq) + 2IO3─ (aq) The solubility product, Ksp , of calcium iodate(V) is expressed as follows. Ksp = [Ca2+(aq)] [IO3─(aq)]2 The solubility product can be found by determining the equilibrium concentration of IO3─ ions in a saturated solution of calcium iodate(V) through a redox titration. Iodate(V) ions, IO3─, react with iodide ions according to the following equation. IO3─ (aq) + 5I⁻(aq) + 6H+ (aq) 3I2 (aq) + 3H2O (l) The iodine produced in this reaction may be titrated against sodium thiosulfate using starch solution as indicator. Thiosulfate ions react with iodine according to the following equation: 2S2O32–(aq) + I2(aq)  S4O62–(aq) + 2I–(aq) In this question, you will prepare a saturated solution of calcium iodate(V) to carry out the redox titration. Using the experimental results, you will determine the solubility product of calcium iodate(V). You are provided with: FA 1 is solid calcium iodate(V), Ca(IO3)2 FA 2 is 0.05 mol dm–3 sodium thiosulfate, Na2S2O3 FA 3 is 0.50 mol dm–3 potassium iodide, KI FA 4 is 0.50 mol dm–3 sulfuric acid, H2SO4 FA 5 is starch indicator Prepara