Copy of KCPSS 2024 4E Chem Prelim P3

] KUO CHUAN PRESBYTERIAN SECONDARY SCHOOL 2024 Preliminary Examination Secondary 4 Express NAME CLASS REG. NO CHEMISTRY 6092/03 Paper 3 Practical 14 August 2024 1 hour 50 minutes Candidates answer on the Question Paper. Setter : Mr. Sam Yew Yishen READ THESE INSTRUCTIONS FIRST Write your name, class and register number on all the work you hand in. Write in dark blue or black pen. You may use a soft 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 page 14. 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. Shift Laboratory For Examiner’s Use 1 17 2 10 3 13 Total 40 This document consists of 13 printed pages and 1 blank page.

2 KCPSS 2024/Sec 4Exp Prelim Chemistry P3 1 Malic acid is a carboxylic acid found in apple juice. The equation for the reaction between malic acid, H 2C4H4O5, and aqueous potassium hydroxide, KOH, is shown. 2KOH + H2C4H4O5  K2C4H4O5 + 2H2O Read all instructions below carefully before starting the experiment in Question 1. Instructions The concentration of aqueous malic acid is determined by titration with aqueous potassium hydroxide, KOH. Thymolphthalein indicator, is used to determine the end-point of the titration. P is apple juice containing malic acid. Q is 0.0500 mol/dm 3 aqueous potassium hydroxide, KOH(aq). I is thymolphthalein indicator. (a) (i) Fill the burette with P. Use the pipette to transfer 25.0 cm 3 of Q into a conical flask. Add a few drops of thymolphthalein indicator, I, to the solution in the conical flask. Ensure the lid is placed back on the vial of I after use. Add P from the burette, swirling the flask constantly. At the end-point, one drop of P would cause the solution to remain colourless for at least 30 seconds. The end-point is when the solution remains colourless for 30 seconds. Record your titration results in the space provided. Repeat the titration as many times as you consider necessary to achieve consistent results. Results [5]

3 KCPSS 2024/Sec 4Exp Prelim Chemistry P3 (ii) From your titration results, obtain an average volume of P to be used in your calculations. Show clearly how you obtained this volume. average volume of P = ………………………cm3 [1] (b) (i) Q is 0.0500 mol/dm3 KOH(aq). Calculate the number of moles of aqueous KOH in 25.0 cm3 of Q. number of moles of aqueous KOH = …………………………mol [1] (ii) Use your answer from (b)(i) to calculate the number of moles of malic acid, H2C4H4O5, in the average volume of P used. number of moles of malic acid = …………………………mol [1] (iii) Use your answer from (b)(ii) to calculate the concentration (mol/dm 3) of malic acid in P. concentration of malic acid in P = ………………………..mol/dm 3 [1] (c) Suggest why the accurate titration of apple juice with aqueous KOH usually produces an average value higher than your answer from (b)(iii). .................................................................................................................................... ............................................................................................................................... [1]

4 KCPSS 2024/Sec 4Exp Prelim Chemistry P3 (d) You are provided copper(II) salt R. (i) Carry out the following tests on R. You are not required to carry out any gas tests. Record your observations in Table 1.1. The volumes given below are approximate and should be estimated rather than measured unless instructed otherwise. Table 1.1 test observations Test 1 Soak the end of a wooden split with deionised water. Dip the wet end of the splint into a sample of salt R . Make sure that the end of the splint is well covered with salt R. Adjust the Bunsen burner to give a blue flame. Place the wet end of the splint in the flame. Test 2 Place about 2 cm depth of dilute nitric acid into the test -tube containing salt R. Add one spatula -load of solid sodium chloride. Insert a rubber bung and shake the test-tube thoroughly to dissolve the solid. Test 3 Add deionised water until the test - tube is half full. Mix the contents of the test-tube thoroughly. [4]

5 KCPSS 2024/Sec 4Exp Prelim Chemistry P3 (ii) Complete Table 1.2 by describing a positive test to identify the anion of the solution obtained in Test 3. Carry out the experimental steps and record its observation in Table 1.2. Table 1.2 description of positive test observation [2] (iii) Explain why dilute nitric acid was added to salt R in Test 2. .............................................................................................................................. ......................................................................................................................... [1] [Total: 17]

6 KCPSS 2024/Sec 4Exp Prelim Chemistry P3 2 A student investigated the effects of concentration on the rate of reaction by measuring the time taken to collect 40 cm 3 of hydrogen gas when magnesium reacts with dilute sulfuric acid. Five experiments were done using the apparatus shown in Fig. 2.1. Fig. 2.1 Experiment 1 • Using a measuring cylinder, 16.0 cm 3 of 1.0 mol/dm3 of dilute sulfuric acid was poured into the conical flask. • Using a second measuring cylinder, 24.0 cm 3 of deionised water was added to the acid in the conical flask. • The apparatus was set up as shown in Fig. 2.1, while ensuring that the inverted measuring cylinder was fully-filled with water. • The rubber bung was removed from the conical flask. • A coiled magnesium ribbon of 5 cm was added into the conical flask and the rubber bung was immediately replaced and the timer was started. • The time taken for 40 cm3 of gas to be collected was measured. Experiments 2 to 5 • The conical flask was rinsed out with deionised water. Dilute sulfuric acid and deionised water for each experiment were added according to the volumes shown in Table 2.2. Table 2.2 experiment volume of dilute sulfuric acid / cm 3 volume of deionised water / cm3 time taken to collect 40 cm3 of gas / s 1 16.0 24.0 72 2 20.0 20.0 45 3 16.0 33 4 32.0 8.0 23 5 40.0 16 rubber delivery tube rubber bung conical flask clamp inverted 100 cm3 measuring cylinder trough water

7 KCPSS 2024/Sec 4Exp Prelim Chemistry P3 (a) (i) Complete Table 2.2 with the two missing volumes. [1] (ii) The rate of reaction can be calculated using the equation given. rate of reaction = volume of gas collected