SAJC 2026 H2Chem Prelim P4 QP

1 [Turn over Name: Class: 25S ST ANDREW’S JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATIONS CHEMISTRY Paper 4 Practical 9476/04 13 Aug 2026 2 hours 30 minutes You must answer on the question paper. You will need: The materials and apparatus listed in the Confidential Instructions Insert INSTRUCTIONS • Answer all questions. • Use a black or dark blue pen. You may use an HB pencil for any diagrams or graphs. • Write your name and class in the boxes at the top of the page. • Write your answer to each question in the space provided. • Do not use an erasable pen. Do not use correction fluid or tape. • You may use an approved calculator. • Qualitative analysis notes are printed in the question paper. • Write the details of the shift and laboratory in the boxes provided. INFORMATION • The total mark for this paper is 50. • The number of marks for each question or part question is shown in brackets [ ]. Shift Laboratory For Examiner’s Use 1 14 2 23 3 13 Total 50 This document consists of 24 printed pages. Any blank pages are indicated.

2 1 Investigating the kinetics of the reaction between thiosulfate ions and acid FA 1 is 0.100 mol dm–3 sodium thiosulfate, Na2S2O3. FA 2 is 1.00 mol dm–3 sulfuric acid, H2SO4. The thiosulfate ion, S2O32–, decomposes when an acid is added according to the equation shown. S2O32–(aq) + 2H+(aq) → S(s) + SO2(aq) + H2O(l) In this experiment, the rate of the reaction is studied by measuring the rate of formation of sulfur using a ‘clock’ method. You will vary the concentration of thiosulfate ions and measure the time taken for a fixed amount of sulfur to be produced. This wi ll be indicated by how long it takes for the solid sulfur forming to obscure the print on the insert. You will perform a series of five experiments. For each experiment you will need to ensure that the same total volume of reaction mixture is used, by adding deionised water as required. For each experiment, you will measure the time, t, for the sulfur to obscure the print on the insert. Note: A small amount of sulfur dioxide gas may be formed in the experiment. It is very important that you avoid inhaling any fumes. As soon as each experiment is complete, add the reaction mixture to the waste container of sodium carbonate solution and rinse the beaker thoroughly. (a) Prepare a table in the space provided on page 4 in which to record, to an appropriate degree of precision: • the volumes of FA 1 (VFA 1) and deionised water used • all values of t • rate The rate of reaction can be calculated using the following formula. rate = 1000 t Experiment 1 1) Use the 50 cm3 measuring cylinder to measure 40.0 cm3 of FA 1 into the 100 cm3 beaker. 2) Use the 25 cm3 measuring cylinder to measure 10.0 cm3 of FA 2. 3) Pour the FA 2 into the same beaker, starting the stopwatch during this addition. 4) Stir the mixture once and place the beaker on the printed insert. 5) Stop the stopwatch when the print on the insert becomes obscured.

3 [Turn over 6) Record the time taken, to the nearest second, in your table. 7) Discard the reaction mixture immediately into the waste container of sodium carbonate solution. 8) Wash out the beaker thoroughly with tap water and then with deionised water. Stand the beaker upside down on a paper towel to drain. Experiment 2 9) Use the 50 cm 3 measuring cylinder to measure 20.0 cm 3 of FA 1 into another 100 cm3 beaker. 10) Use the same 50 cm3 measuring cylinder to measure 20.0 cm3 of deionised water into the same beaker. 11) Use the 25 cm3 measuring cylinder to measure 10.0 cm3 of FA 2. 12) Pour the FA 2 into the same beaker, starting the stopwatch during this addition. 13) Stir the mixture once and place the beaker on the printed insert. 14) Stop the stopwatch when the print on the insert becomes obscured. 15) Record the time taken, to the nearest second, in your table. 16) Discard the reaction mixture immediately into the waste container of sodium carbonate solution. 17) Wash out the beaker thoroughly with tap water and then with deionised water. Stand the beaker upside down on a paper towel to drain. Experiments 3 - 5 Carry out three further experiments to investigate how using different volumes of FA 1 affects the reaction time. Do not use a volume of FA 1 that is less than 15.0 cm3. In each experiment, you should adjust the volume of deionised water in step 1 0 to ensure the same total volume of reaction mixture is used. You should alternate the use of the two 100 cm3 beakers. Record all your results in a table. You should include all volumes, the time taken and the reaction rate for each of your five experiments in your table. Keep FA 1 for use in Question 2. Keep FA 2 for use in Questions 2 and 3.

4 Results [5]

5 [Turn over (b) (i) Plot a graph of rate on the y -axis against volume of FA 1 on the x-axis on the grid in Fig 1.1. Start each axis at the origin (0,0). Draw the best-fit line. Fig 1.1 [3]

6 (ii) From your graph, what conclusion can be drawn about the relationship between the rate of reaction and the volume of FA 1 used? Explain your answer. …………………………………………………………………………………………... …………………………………………………………………………………………... …………………………………………………………………………………………... …………………………………………………………………………………………... [2] (iii) Using your graph, determine the time it would take for the print to be obscured if 7.5 cm3 of FA 1, 32.5 cm3 of water and 10.0 cm3 of FA 2 had been used. Show clearly on the graph how you worked out your answer. time for print to be obscured = ……………………………. s [2] (c) (i) A student found that the reaction was first order with respect to [H+]. Predict and explain how the value of t in Experiment 1 would be affected if hydrochloric acid of the same concentration and volume had been used instead of FA 2. …………………………………………………………………………………………... …………………………………………………………………………………………... …………………………………………………………………………………………... [1]

7 [Turn over (ii) Predict and explain how the value of t in Experiment 1 would be affected if a 250 cm3 beaker with a larger base area was used instead of the 100 cm3 beaker. …………………………………………………………………………………………... …………………………………………………………………………………………... …………………………………………………………………………………………... [1] [Total: 14]

8 2 Determination of the value x of an iodate ion, IOx– Iodate ions contain iodine and oxygen. They have the formula IOx– where x is an integer. (a) In this experiment you will determine the value of x in an iodate. You will first react IOx– with an excess of iodide ions, I–, to form iodine, I2. The amount of iodine produced is then determined by titration with thiosulfate ions, S2O32–. I2(aq) + 2S2O32–(aq) → 2I–(aq) + S4O62–(aq) FA 1 is 0.100 mol dm–3 sodium thiosulfate, Na2S2O3. FA 2 is 1.00 mol dm–3 sulfuric acid, H2SO4. FA 3 is a solution containing 0.0140 mol dm–3 IOx– ions. FA 4 is 0.500 mol dm–3 potassium iodide, KI. Solution S is starch solution. (i) Titration 1) Fill the burette with FA 1. 2) Use the pipette to transfer 25.0 cm3 of FA 3 into a 250 cm3 conical flask. 3) Use the 25 cm3 measuring cylinder to transfer 10.0 cm3 of FA 2 to the same conical flask. 4) Use the same measuring cylinder to transfer 10.0 cm3 of FA 4 to the same conical flask. 5) Run FA 1 from the burette into this flask until the solution turns yellow. 6) Add 10–15 drops of Solution S to the solution in the conical flask. 7) Continue to add more FA 1 from the burette until the blue-black colour just disappears. 8) Record your titration results in Table 2.1 on page 9. Make certain that your recorded results show the precision of your working. 9) Repeat steps 1 to 8 as necessary until consistent results are obtained. Keep FA 3 for use in Qu