23MIPrelimAS (H2 Chem Paper 4)

Class Adm No Candidate Name: This question paper consists of 18 printed pages and 0 blank page. 2023 Preliminary Examination Pre-University 3 H2 CHEMISTRY 9729/04 Paper 4 Practical 30 August 2023 2 hours 30 minutes Candidates answer on the Question paper. READ THESE INSTRUCTIONS FIRST Do not turn over this question paper until you are told to do so. Write your name, class and admission number in the spaces at the top of this page. 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 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. Qualitative Analysis Notes are printed on pages 17 and 18. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. Question 1 2 3 Total Marks 18 24 13 55 Class Adm No

2 Answer all the questions in the spaces provided. 1 To determine the effect of concentration changes on the rate of a reaction FA 1, 0.0200 mol dm-3 aqueous potassium iodate(V), KIO3 FA 2, 0.0200 mol dm-3 aqueous sodium hydrogen sulfite, NaHSO3 FA 3, 0.0600 mol dm-3 aqueous sulfuric acid, H2SO4 FA 4 is starch solution In this experiment, the Landolt-Iodine clock reaction is illustrated by the following equations. IO3 - + 3HSO3 - → I- + 3SO4 2- + 3H+ equation 1 IO3 - + 5I− + 6H+ → 3I2 + 3H2O equation 2 3I2 + 3HSO3 - + 3H2O → 6I- + 3SO4 2- + 9H+ equation 3 Any I2 produced in equation 2 while HSO 3 - ions still remain in the solution is rapidly reduced to I- in equation 3. Once all the HSO 3 - ions have been used up, I2 will accumulate in the solution. When this happens, the iodine can no longer be converted back to iodide ions. The presence of iodine can be confirmed from the blue-black colour produced upon addition of starch. Overview of experiment You will carry out five similar experiments, 1 to 5 with varying concentrations of IO3 -. In each experiment, you will be required to prepare two solutions – solution A and solution B. Note:  Solution B should only be prepared once for all five experiments, while solution A must be prepared five times.  Perform the experiments in order, from experiment 1 to 5.  The measuring apparatus used to prepare solutions A and B must be kept separate at all times. For each experiment, you will record the time taken , t, for the solution to turn blue-black . The rate of the reaction is given to be, r = 𝑖𝑛𝑖𝑡𝑖𝑎𝑙 [𝐻𝑆𝑂3 −] 𝒕 mol dm-3 s-1. You will record in a table in the space provided on page 4, the following values for each of the five experiments.  all volumes of FA 1 and deionised water used to prepare solution A,  values of t, to the nearest second,  calculated values of initial [IO3 −] in the reaction mixture to 3 significant figures, and  calculated values of r, to 3 significant figures. Note: volumes used to prepare solution B need not be recorded.

3 [Turn over (a) (i) Preparing solution B 1. Using a pipette, transfer 25.0 cm 3 of FA 2 to the 250 cm3 volumetric flask. 2. Using an appropriate measuring cylinder , transfer to the same volumetric flask  50.0 cm3 of FA 4, then,  50.0 cm3 of FA 3. 3. Make up the solution to 250 cm 3 with deionised water and mix thoroughly. This is solution B. (ii) Preparing solution A 1. Fill a burette with FA 1. 2. Fill another burette with deionised water. 3. Transfer 10. 00 cm 3 of FA 1 , followed by 10.00 cm 3 of deionised water into a 100 cm3 conical flask. This is solution A. (iii) Experiment 1 1. Using an appropriate measuring cylinder, measure out 10.0 cm 3 of solution B. 2. Add solution B from the measuring cylinder into the conical flask containing solution A. Swirl and start the stopwatch immediately upon mixing. 3. Stop the stopwatch when the end ‑point is reached. 4. Record this value of t, to the nearest second. At the end of experiment 1, wash the conical flask and allow it to stand to drain on a paper towel. (iv) Experiments 2 to 5 1. Repeat step 3 in (a)(ii) and the procedures in (a)(iii) a further four times to perform experiments 2 to 5. 2. In step 3 in (a)(ii), you are to use different volumes of FA 1 and deionised water to prepare a different solution A for each experiment. You should use a minimum volume of 2.00 cm 3 of FA 1 and a maximum volume of 10.00 cm 3 of FA 1 . By adding the appropriate volume of deionised water, ensure that the total volume of solution A is always 20.00 cm3.

4 (b) (c) The concentration of FA 2 in the reaction mixture remains the same in each experiment. (i) Calculate the amount of FA 2, HSO3 -, in 250 cm3 of solution B. Amount of FA2 added into the volumetric flask = 25/1000 x 0.02 = 0.000500 mol amount of FA 2 in 250 cm3 = ……………………………[1] (ii) Calculate the amount of FA 2, HSO3 -, in 10 .0 cm3 of solution B that was measured out for reaction. Amount of HSO3 - in 10 cm3 = 0.000500 / 25 = 2.00 x 10-5 mol ; amount of FA 2 in 10.0 cm3 = ……………………………[1] (iii) Hence, determine the concentration of FA 2, [HSO3 -], in each reaction mixture. [FA 2] in each reaction mixture = (2.00 x 10-5) / (30/1000) = 6.67 x 10-4 mol dm-3 [FA 2] = ………………………………[1] Results Vol of FA1 /cm3 Vol of H2O /cm3 t / s initial [IO3 −] / mol dm-3 r / mol dm-3 s-1 1 10.00 10.00 13 0.00667 0.0000513 2 7.00 13.00 19 0.00467 0.0000351 3 5.00 15.00 31 0.00333 0.0000215 4 3.00 17.00 63 0.00200 0.0000106 5 2.00 18.00 110 0.00133 0.00000607 Total volume for each experiment = 30.0 cm3 Table with correct headers and units – 1m Correct precision (2dp for volumes, nearest sec for t, 3sf for calculated values) – 1m Appropriate volumes of FA 1 chosen and correct volume of water added – 1m Correct calculation of [IO3 −] to 3sf – 1m Correct calculation of r to 3sf – 1m Sample calculation of initial [IO3 −] for Expt 1 Amount of FA1 added = 10/1000 x 0.02 = 0.000200 mol [IO3 −] = 0.000200 / (30/1000) = 0.00667 mol dm-3 [5]

5 [Turn over (d) Plot a graph of rate, r, on the y‑axis against initial [IO3 −] on the x‑axis. Draw an appropriate line taking into account all of your plotted points. [3] 1m for axes and label 1m for correctly plotted points 1m for best fit (line to take into consideration coordinate 0,0)

6 (e) (i) The rate equation for the reaction is shown below. r = k [H+][HSO3 −][IO3 -]x Use your graph to deduce the order of reaction, x, with respect to the concentration of IO3 - ions. order of reaction, x = ................................ explanation rate order = 1 ; A straight line graph is obtained which shows that the rate is directly proport ional to the change in concentration of IO3 -. ; ....................................................................................................................................[2] (ii) Hence, calculate the value of the rate constant, k, given that the [H+] in each reaction mixture is 0.00800 mol dm-3. State the units of k clearly. Using expt 1, 0.0000513 = k (0.008)( 6.67 x 10-4)(0.00667) k = 1440 mol-2 dm6 s-1 1m for answer 1m for units e.c.f awarded k = ………………………………[2]

7 [Turn over (iii) Using your graph, calculate the volume of FA 1 needed to prepare solution A so that the reaction mixture turns bl