Northvista 2025 Chemistry Sec 4 Prelim Paper 3

NORTH VISTA SECONDARY SCHOOL Preliminary Examination 2025 Secondary 4 Express CANDIDATE NAME CLASS __________________________________________________________________________ CHEMISTRY 6092/03 22 August 2025 Paper 3 Practical 1 hour 50 minutes Candidates answer on the Question Paper READ THESE INSTRUCTIONS FIRST Write your name, class and register number on all the work you hand in. Give details of the practical shift and laboratory where appropriate, in the boxes provided. Write in dark blue or black pen. You may use an HB 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 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 12. 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. This document consists of 12 printed pages and 1 blank page. [ Turn over INDEX NUMBER For Examiner’s Use 1 2 3 4 Total 4 0 Shift Laboratory

2 1 You are provided with two solutions. Solution R is 4.00 g/dm3 sodium hydroxide. Solution S is prepared by adding an unknown mass of magnesium oxide to 0.50 dm3 of 0.100 mol/dm3 of dilute sulfuric acid. You are to determine the concentration of the acid remaining in S, by titrating R with S and to calculate the mass of magnesium oxide that has been added to the dilute sulfuric acid. Read all the instructions below carefully before starting the experiment in Question 1. Instructions (a) (i) Fill the burette with S. Pipette 25.0 cm3 of R into a conical flask. Add three drops of bromothymol blue indicator. Your solution should turn blue. Add S from the burette to the flask until one drop just turns the solution permanently green. Record your titration results in an appropriate format in the space provided. Repeat the titration as many times as you consider necessary to achieve consistent results. Results [5] (ii) From your titration value, obtain the average volume of S used. Show clearly how you obtained this volume. average volume of S used = …………….………………….[1]

3 (b) (i) R is 4.00 g/dm3 of sodium hydroxide solution. Calculate its concentration in mol/dm3 [Ar of Na, 23; O, 16; H, 1]. concentration ………………………………mol/dm3 [1] (ii) Using your answer from (a)(ii), calculate the concentration of sulfuric acid in mol/dm 3 that is present in solution S. concentration ………………………………mol/dm3 [2] (iii) Initially, 0.50 dm3 of 0.100 mol/dm3 of dilute sulfuric acid was used to prepare solution S. Using your answer in b(ii), calculate the number of moles of sulfuric acid that reacted with magnesium oxide. ………………………………mol [2]

4 (iv) Using your answer in (iii), calculate the number of moles of magnesium oxide that has reacted with sulfuric acid. ………………………………mol [1] (v) Using your answer in (iv), calculate the mass, in grams, of magnesium oxide that has reacted with sulfuric acid [Ar of Mg, 24; O, 16]. ………………………………g [2] (c) A student did the experiment without realising that there is a large air space in the pipette as she draws the solution R using the pipette. Describe and explain the effect this would have on the calculation of the mass of magnesium oxide that has been added to sulfuric acid. ………….…………………………………………………….………………………………………..… ………….…………………………………………………….………………………………………..… ………….…………………………………………………….…………………………………...…..[2] [Total: 16]

5 2 You are going to investigate the thermal stability of three metal carbonates. You are provided with three samples of metal carbonates, W, X and Y in boiling tubes. Read all the instructions carefully before starting the experiments in Question 2. Instructions You are going to do three experiments. Experiment 1 (a) Remove the stopper from the boiling tube labelled W. (b) Use the balance to find the mass of the boiling tube and its contents. R ecord the mass in Table 2.1. (c) Set up the experiment as shown in Fig. 2.1. Add about 3 cm depth of limewater in a clean test - tube. (d) Heat the boiling tube gently and then strongly for 3 minutes. (e) Record any other changes observed in Table 2.1. (f) Remove the boiling tube from set-up and leave the boiling tube and its content to cool completely. Find the mass of the test-tube and its contents upon cooling and record in Table 2.1. (g) You may continue with experiments 2 and 3 while waiting for the boiling tube to cool. Fig. 2.1 Experiment 2 (a) Remove the stopper from the boiling tube labelled X. (b) Repeat steps (b) to (f) from experiment 1. (c) You may continue with experiment 3 while waiting for the boiling tube to cool. Experiment 3 (a) Remove the stopper from the boiling tube labelled Y. (b) Repeat steps (b) to (f) from experiment 1. boiling tube with metal carbonate Bunsen burner clamp stand clamp delivery tube limewater test-tube

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7 (a) Complete Table 2.1. Table 2.1 metal carbonate mass of boiling tube and contents before heating / g mass of boiling tube and contents after heating / g other observation(s) W X Y [4] (b) Using the results in Table 2.1, arrange the thermal stability of the three metal carbonates from the most thermally stable to the least thermally stable. Explain your answer. ………….…………………………………………………….………………………………………..… ………….…………………………………………………….………………………………………..… ………….…………………………………………………….………………………………………..[2] (c) A student mentioned that the change in mass recorded can be used to determine the amount of metal carbonate given in the boiling tube. Explain whether you agree with the statement. ………….…………………………………………………….………………………………………..… ………….…………………………………………………….………………………………………..… ………….…………………………………………………….………………………………………..[1] (d) A student found out that there is another way of bubbling gas into limewater. The method involves the use of a dropper pipette to draw the gas sample and insert into limewater. Describe the disadvantage of using this method over the use of the delivery tube. ………….…………………………………………………….………………………………………..… ………….…………………………………………………….………………………………………..[1]

8 (e) You are provided with a sample of solution A containing the same cation found in metal carbonate Y. Read all the instructions carefully before starting the experiments in Question 2e. You should test and identify any gases evolved. The volumes given below are approximate and should be estimated rather than measured, unless otherwise stated. Test Procedure Observation 1 Add about 2 cm depth of solution A into a clean test-tube. To this test -tube, add one piece of magnesium ribbon and leave it to stand