2023 SAJC H2 Prelim P4 Questions

1 [Turn Over Name: Class: ST ANDREW’S JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION CHEMISTRY Paper 4 Practical 9729/04 14 August 2023 2 hours 30 minutes Additional Materials: Qualitative Analysis Notes Shift Laboratory For Examiner’s Use 1 2 3 4 Total This document consists of 26 printed pages including this page. 1. Determination of x in hydrated copper( II) sulfate, CuSO 4xH2O by titrimetric 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 a soft 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, where appropriate. You may lose marks if you do not show your working or if you do not use appropriate units. The number of marks is given in the brackets [ ] at the end of each question or part question. 14 15 13 13 55

2 [Turn Over analysis The formula of hydrated copper( II) sulfate is CuSO 4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, S 2O3 2. The iodine is formed by the reaction of copper( II) ions, Cu2+, with iodide ions, I. 2Cu2+ + 4I  2CuI + I2 2S2O3 2 + I2  S4O6 2 + 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 hydrated copper(II) sulfate, FA 4 1. Weigh accurately about 3.50 g of FA 1 in a clean and dry weighing bottle . Record the mass of FA 1 used on page 4. 2. Transfer FA 1 into a 100 cm 3 beaker . Add approximately 80 cm3 of deionised water to FA 1 in the beaker and stir until the salt has dissolved. Rinse the weighing bottle with deionised water several times, adding each rinsing to the beaker. 3. Pour the contents carefully into a 250 cm 3 volumetric flask. Rinse the beaker with deionised water and add these washings to the flask. 4. Fill the flask to the mark with deionised water and shake to ensure thorough mixing. 5. Label the solution FA 4. (b) (i) Titration of iodine against FA 2

3 [Turn Over 1. Fill a burette with FA 2. 2. Using a pipette, transfer 25.0 cm3 of FA 4 into a conical flask. 3. Use a measuring cylinder to add approximately 7 .0 cm3 of FA 3 into the same conical flask. This will form a white precipitate in a brown solution. 4. Titrate this mixture with FA 2. When the brown solution becomes pale, add 1.0 cm3 of starch indicator. The mixture will turn a blue-bl