Copy of PLMGSS 2024 4E Chem P3 QP

1 CANDIDATE NAME CLASS CLASS INDEX NO CENTRE NUMBER S INDEX NUMBER CHEMISTRY 6092/03 Paper 3 Practical 23 August 2024 Redox Reactions, Moles, Rates of Reactions, Energy Changes 1 hour 50 minutes READ THESE INSTRUCTIONS FIRST Write your name, class, class index number, centre number and O level index number on all the cover page. Give details of the practical shift and laboratory where appropriate, in the boxes provided. 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 11. At the end of the examination, fasten all your work securely together, if applicable. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 11 printed pages. Shift Laboratory For Examiner’s Use 1 /18 2 /12 3 /10 Total /40 Paya Lebar Methodist Girls’ School (Secondary) Preliminary Examination 2024 Secondary 4 Express / G3 [Turn Over

2 1 Some cleaning products contain a solution of sulfamic acid. You are going to determine the concentration of sulfamic acid in a sample of a cleaning product by titration with sodium hydroxide. The sulfamic acid can be represented by the formula, HA. The equation for the reaction occurring in the titration is shown. HA + NaOH → NaA + H2O Read all the instructions below carefully before starting the experiment in Question 1. Instructions P is 0.200 mol / dm3 sodium hydroxide. Q contains aqueous sulfamic acid. The solution was made by diluting a sample of 100 cm3 of the cleaning product to 1.00 dm3 by adding deionised water. T is thymolphthalein indicator. (a) (i) Fill the burette with P. Use the pipette to transfer 25.0 cm3 of Q into a conical flask. Add a few drops of the thymolphthalein indicator, T, to the solution in the conical flask. Ensure the lid is placed back on the container of T after use. Add P from the burette, swirling the flask constantly. At the end-point, one drop of P produces a blue colour that does not disappear on swirling. 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 (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) P is 0.200 mol / dm3 sodium hydroxide. Use your answer from (a)(ii) and the equation for the reaction to calculate the number of moles of sulfamic acid in 25.0 cm3 of Q. number of moles of sulfamic acid in 25.0 cm3 of Q ………………………………mol [1] (ii) Use your answers from (b)(i) to calculate the concentration, in mol / dm3, of sulfamic acid in the sample of the cleaning product. concentration of sulfamic acid in cleaning product ………………………………mol / dm3 [2] [Turn Over

4 (c) The label on the bottle of cleaning product gives the concentration of sulfamic acid in g / dm3. To convert your answer from (b)(ii) to g / dm3, it is necessary to know the relative molecular mass, Mr, of sulfamic acid. The Mr can be determined by reacting some solid sulfamic acid with aqueous sodium carbonate and measuring the volume of carbon dioxide produced. The equation for the reaction is shown. 2HA + Na2CO3 → CO2 + H2O + 2NaA (i) Use this information to outline a method to determine the Mr of sulfamic acid. Your method should use gas collection by displacement of water. In your method you should include: • the apparatus you would use • the measurements you would take • an explanation of how you would use your results to determine the Mr of sulfamic acid. You can assume the apparatus and reagents normally found in a school laboratory are available. You may wish to use a labelled diagram to illustrate your answer. ………………………………………………………………………………………………..... ………………………………………………………………………………………………..... .……………………………………………………………………………………………….... ………………………………………………………………………………………………..... ………………………………………………………………………………………………..... .……………………………………………………………………………………………….... ……………………………………………………………………………………………….....

5 .……………………………………………………………………………………………….... ………………………………………………………………………………………………..... .……………………………………………………………………………………………….... ………………………………………………………………………………………………..... .……………………………………………………………………………………………….... .……………………………………………………………………………………………….... ………………………………………………………………………………………………..... .……………………………………………………………………………………………….... .…………………………………………………………………………………………...… [5] (ii) Carbon dioxide is soluble in water. Suggest how this may cause your calculated value for the Mr of sulfamic acid to be different from its theoretical value. Explain your answer. .……………………………………………………………………………………………….... ………………………………………………………………………………………………..... .……………………………………………………………………………………………….... .……………………………………………………………………………………...……… [3] (iii) Suggest and explain one change you could make to your experiment to improve the accuracy of your calculated value for Mr. change ………………………………………………………………………………..……..... explanation ………………………………………………………………………..………….. ………………………………………………………………………………………………..… [1] [Total: 18] [Turn Over

6 2 Metal carbonate decomposes on heating. The following equation shows the decomposition of carbonate of metal M, where M has a charge of +2. MCO3 → MO + CO2 You are supplied with two samples of metal carbonates where the metals have charge of +2. The more reactive a metal is, the greater the thermal stability of the metal carbonate, the harder it is to decompose the metal carbonate. You are to determine the order of reactivity between the two metals. Read all the instructions carefully before starting the experiment in Question 2. Instructions X is carbonate of metal R. Y is carbonate of metal S. (a) (i) Use the electronic balance to find the mass of an empty test-tube. Add about 1.00 g of X to the test-tube and then find the mass of the test-tube and its contents. Record the colour of the metal carbonate. Heat the test-tube and contents strongly for 1 minute. Record any colour change. Leave the test -tube and its contents to cool to room temperature before finding the mass of the test-tube and its contents. Repeat the heating and cooling of the test-tube and its content up to 3 mins. Repeat the experiment with 1.00 g of Y. Record your results in an appropriate format in the space provided. Results Metal carbonate X: carbonate of metal R Y: carbonate of metal S Colour of carbonate before heating Colour change during heating/cooling Mass of test-tube and contents before heating /g Mass of test-tube and contents after heating for 1 min /g Mass of test-tube and contents after heating