2019 SAJC H2 Chem Prelim P4 QP

[Turn Over NAME Class ST ANDREW’S JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION Chemistry (9729) Paper 4 Practical 27 Aug 2019 2.5 hours Candidates answer on the Question Paper Additional Materials : As listed in the Confidential Instructions : Insert READ THESE INSTRUCTIONS FIRST. Write your name and class on all the work you hand in. Give details of the practical shift and laboratory in the boxes provided above. 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 the 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. Shift Laboratory Qualitative Analysis Notes are printed on pages 21 and 22. The number of marks is given in the brackets [ ] at the end of each question or part question. For Examiner’s use: Question Practical Planning Total Marks 44 11 55 This document consists of 22 printed pages.

2 1 To standardise a 0.0 3 mol dm–3 of iron(III) chloride solution and determine the concentration of sodium thiosulfate solution. (a) Planning FA1 is a standard solution containing 0.03 mol dm–3 of FeCl3 solution. You are to design an experiment to show how FA1 is prepared using solid FeCl3. You are provided with : a solid sample of approximately 1.50 g of FeCl3 (Mr = 162.3), 250 cm3 volumetric flask and the usual laboratory apparatus In your plan, you should include details on:  the mass of FeCl3(s) you use with justification,  the apparatus you would use, and  the procedures which you would follow. Do not carry out this plan as FA1 is provided for you to continue with 1(b). ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… [3]

3 [Turn Over 1 (b) In addition to FA1, you are also provided with the following: FA2 is 0.060 mol dm–3 potassium iodide, KI. FA3 is aqueous sodium thiosulfate, Na2S2O3. When FA1 is combined with FA3, a complex, [Fe(S2O3)2]–, is formed. Reaction 1: Fe3+(aq) + 2S2O32–(aq) ⇌ [Fe(S2O3)2]–(aq) To 1 cm3 of FA3 in a test–tube, add 2–3 drops of FA1 and shake them thoroughly. State the colour of the complex formed. Colour : ………………………… [1] (c) A student aimed to determine the concentration of FA3 using volumetric analysis involving the use of FA1 and FA2. Reaction 2: 2Fe3+(aq) + 2I–(aq) → 2Fe2+(aq) + I2(aq) Reaction 3: I2(aq) + 2S2O32–(aq) → 2I–(aq) + S4O