2025 Sec 4 Pure Chem Practical (15 Schools)

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Name: ………………………………………………….. ( ) This Question Paper consists of 13 printed pages including this page. [Turn over ASSUMPTION ENGLISH SCHOOL PRELIMINARY EXAMINATION 2025 CHEMISTRY 6092 / 03 ASSUMPTION ENGLISH SCHOOL ASSUMPTION ENGLISH SCHOOL ASSUMPTION ENGLISH SCHOOL ASSUMPTION ENGLISH SCHOOL ASSUMPTION ENGLISH SCHOOL ASSUMPTION ENGLISH SCHOOL ASSUMPTION ENGLISH SCHOOL ASSUMPTION ENGLISH SCHOOL ASSUMPTION ENGLISH SCHOOL ASSUMPTION ENGLISH SCHOOL ASSUMPTION ENGLISH SCHOOL ASSUMPTION ENGLISH SCHOOL ASSUMPTION ENGLISH SCHOOL ASSUMPTION ENGLISH SCHOOL ASSUMPTION ENGLISH SCHOOL ASSUMPTION ENGLISH SCHOOL ASSUMPTION ENGLISH SCHOOL ASSUMPTION ENGLISH SCHOOL ASSUMPTION ENGLISH SCHOOL ASSUMPTION ENGLISH SCHOOL LEVEL: Sec 4 Express DATE: 26 August 2025 CLASS: Sec 4/1 DURATION: 1 hour 50 minutes Additional Materials provided: NIL INSTRUCTIONS TO CANDIDATES Do not open this booklet until you are told to do so. Write your NAME and INDEX NUMBER at the top of this page. Write in dark blue or black pen on both sides of the paper. You may use a soft pencil for any diagrams, graphs, tables or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer ALL questions in the spaces provided. The number of marks is given in brackets [ ] at the end of each question or part question. Qualitative Analysis Notes are printed on page 13. For Examiner’s use: Total / 40 www.KiasuExamPaper.com 3

2 6092/03/4E/PRELIM/2025 Answer all questions in the spaces provided. 1 Ethanol is the main component of wine. You are going to use titration to determine the concentration of ethanol in a sample of wine. Fenton’s reagent is a mixture of hydrogen peroxide and trace amounts of iron(II) sulfate. The iron( II) sulfate acts as a catalyst for this reaction. When excess Fenton’s reagent is added to ethanol, the ethanol is oxidised to form ethanoic acid and water according to the chemical equation. C2H5OH + 2 H2O2 → CH3COOH + 3 H2O The amount of unreacted Fenton’s reagent can be found by titration with acidified potassium manganate(VII). The ionic equation for the reaction is shown. 2 MnO4− + 5 H2O2 + 6 H+ → 2 Mn2+ + 5 O2 + 8 H2O Read all the instructions carefully before starting the experiments in Question 1. Instructions P is 0.2 mol/dm 3 aqueous potassium manganate(VII). Q is a solution containing ethanoic acid and unreacted Fenton’s reagent which is formed by adding 100 cm3 of 0.2 mol/dm3 Fenton’s reagent to 5 cm3 of wine. R is dilute sulfuric acid. (a) (i) Fill a burette with P. As the colour of the solution is intense, you should obtain burette readings by reading the top of the meniscus. Use a pipette to transfer 25.0 cm3 of Q into a conical flask. Use a measuring cylinder to measure and transfer 20.0 cm 3 of R into the same conical flask. Add P from the burette to the flask. At first, the purple colour disappears rapidly. At the end point, one drop of P produces a permanent pale pink colour that does not disappear on swirling. www.KiasuExamPaper.com 4

3 6092/03/4E/PRELIM/2025 [Turn over Record your titration results in the space provided. Repeat the titration as many times as you consider necessary to achieve consistent results. Results [5] (ii) From your titration results, obtain the average volume of P to be used in your calculations. Show clearly how you obtained this volume. average volume of P = ……………..… [1] (b) (i) Calculate the number of moles of potassium manganate(VII) used to react with the unreacted Fenton’s reagent in Q. number of moles of potassium manganate(VII) = ….………..… [1] (ii) Use your answer from (b)(i) and the equation for the reaction to calculate the number of moles of unreacted Fenton’s reagent in Q. number of moles of unreacted Fenton’s reagent in Q = ….………..… [1] www.KiasuExamPaper.com 5

4 6092/03/4E/PRELIM/2025 (iii) Use your answer from (b)(ii) to calculate the volume of unreacted Fenton’s reagent in Q. volume of unreacted Fenton’s reagent in Q = ….………..… [1] (iv) Use your answer from (b)(iii) to calculate t he volume of Fenton’s reagent that reacted with ethanol. volume of Fenton’s reagent that reacted with ethanol = ….………..… [1] (v) Use your answer from (b)(iv) to calculate the concentration of ethanol in the sample of wine. concentration of ethanol in the sample of wine = ……….………..… [4] www.KiasuExamPaper.com 6

5 6092/03/4E/PRELIM/2025 [Turn over (c) Potassium manganate( VII) is unreactive to the ethanoic acid in Q. However, at extremely high temperatures, Potassium manganate(VII) can also oxidise ethanoic acid. Describe how your calculated concentration of ethanol would change if the experiment was conducted at high temperatures. ……………………………………………………………………………….. ……………………………………………………………………………….. ……………………………………………………………………………….. ……………………………………………………………………………….. [2] (d) Identify one source of error for this experiment and suggest an improvement that would avoid this source of error. source of error ……………………………………………………………… ……………………………………………………………………………….. improvement ……………………………………………………………….. ……………………………………………………………………………….. [2] [Total: 18] www.KiasuExamPaper.com 7

6 6092/03/4E/PRELIM/2025 2 Read all the instructions carefully before starting the experiments in Question 2. You are provided with a sample of dilute acid X, and a stoppered boiling tube containing salt Y. Instructions (a) Carry out the following tests. You should test and identify any gases evolved. Record your observations in the table. The volumes given below are approximate and should be estimated rather than measured. If no observable change is observed for a test, write 'no observable change'. test observations Add about 2 cm depth of X into a clean test-tube. Add a few drops of barium nitrate. [1] Add about 2 cm depth of X into a clean test-tube. Add a few drops of silver nitrate. [1] Add about 2 cm 3 of X into the boiling tube containing Y. Add an equal volume of aqueous sodium hydroxide. Gently warm the mixture. [3] (b) Deduce the formulae of acid X and salt Y. X is ……………………………… Y is ……………………………… [1] [Total: 6] www.KiasuExamPaper.com 8

7 6092/03/4E/PRELIM/2025 [Turn over 3 Read all the instructions carefully before starting the experiments in Question 3. You are given the same acid X from Question 2. You are also provided with 5 stoppered test-tubes containing Z which is copper(II) carbonate. It is known that X and Z react to form carbon dioxide gas. The evolution of carbon dioxide gas causes visible bubbling to occur in the reaction flask. You will investigate the relationship between the rate of reaction and the concentration of X. The rate of reaction can be estimated by measuring the time taken for effervescence in the reaction flask to stop. Experiment 1 • Use a 10 cm 3 measuring cylinder to measure 10.0 cm3 of X. • Pour X into the test-tube containing Z and immediately start the stopwatch. Stir the solution constantly using a glass rod. • Stop the stopwatch as soon as you can no longer see visible effervescence in the test-tube. Record the time to the nearest second in the results table on page 8. • Empty the contents of the test-tube into the WASTE container provided. Experiment 2 • Use a 10 cm 3 measuring cylin