RI Prelims P4_Qns

- 1 - © Raffles Institution 2017 9729/A/17 [Turn Over CANDIDATE NAME ( ) CLASS 17S0 RAFFLES INSTITUTION 2017 YEAR 6 PRELIMINARY EXAMINATION Higher 2 CHEMISTRY Paper 4 Practical 9729/04 17 August 2017 2 hours 30 minutes Do NOT turn over the Question Booklet until you are told to do so. READ THESE INSTRUCTIONS FIRST. Write your name and class on the space provided when instructed to do so. Give details of the practical shift and laboratory where appropriate, in the space provided. Write in dark blue or black pen. You may use a 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 number of marks is given in brackets [ ] at the end of each question or part question. 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 17 and 18. Shift Laboratory Bench Number For Examiner’s Use Question Marks 1 / 24 2 / 16 3 / 15 Total / 55 This Question Paper consists of 18 printed pages.

- 2 - © Raffles Institution 2017 9729/A/17 [Turn Over 1 Determination of x in hydrated copper(II) sulf ate, CuSO 4xH2O by titrimetric analysis The formula of hydrated copper (II) sulfate is CuSO4xH2O, where x represents the number of moles of water of crystallisation in one mole of the compound. You are to determine the value of x by titrating a solution of iodine, I2, with a solution of thiosulfate ions, S2O32. The iodine is formed by the reaction of copper(II) ions, Cu2+, with iodide ions, I. 2Cu2+ + 4I  2CuI + I2 2S2O32 + I2  S4O62 + 2I You are provided with the following. FA 1 is hydrated copper(II) sulfate, CuSO4xH2O. FA 2 is 0.050 mol dm3 sodium thiosulfate, Na2S2O3. FA 3 is 1.0 mol dm3 potassium iodide, KI. (a) Preparation of aqueous copper(II) sulfate, FA 4 1. Weigh accurately about 3.1 g of FA 1 in a clean and dry weighing bottle . Record the mass used in an appropriate format in the space provided on page 3. 2. Transfer the FA 1 quantitatively into a 100 cm3 beaker and dissolve it in some deionised water. Rinse the weighing bottle with deionised water several times, adding each rinsing to the beaker. Using a gl