Copy of AMKSS 2024 Chem P3

1 AMKSS 4E Prelim Exam 6092/03/2024 [Turn Over ANG MO KIO SECONDARY SCHOOL PRELIMINARY EXAMINATION 2024 SECONDARY FOUR EXPRESS CHEMISTRY 6092/03 Paper 3 16 August 2024 1 hour 50 minutes Setter: Mrs Joselyn Luei Candidates answer on the Question Paper. No Additional Materials are required. READ THESE INSTRUCTIONS FIRST Write your Name, Class and Index Number in the spaces at the top of this paper. Write in dark blue or black pen. You may use a 2B pencil for any diagrams or graphs. Do not use staples, paper clips, highlighters, glue or correction fluid/tape. Answer all the questions in the spaces provided on the Question Paper. Notes for qualitative analysis are printed on pages 13 and 14. 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. 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. For Examiner’s use 1 2 3 4 TOTAL This document consists of 14 printed pages. Candidate Name Form Class Index Number

2 AMKSS 4E Prelim Exam 6092/03/2024 1 Mangalloy is made by alloying steel with manganese. The percentage by mass of manganese in mangalloy can be determined by converting all the manganese in the alloy into aqueous manganate(VII) ions and then using the solution to titrate a solution containing iron(II) ions. No indicator is needed for this titration as the products of the reaction are almost colourless and one drop of aqueous manganate(VII) ions in excess produces a permanent pale pink colour. G is an aqueous solution of manganate(VII) ions, MnO 4-. The solution was prepared by converting all the manganese in a 2.12 g sample of mangalloy into manganate(VII) ions and making the final volume up to 250 cm3 by adding water. H is a solution which initially contained 0.0800 mol/dm 3 iron(II) ions dissolved in an unknown acid. (a) Put G into the burette. The colour of G makes it difficult to see the bottom of the meniscus so you should take all your readings using the top of the meniscus. Pipette 25.0 cm3 portion of H into a conical flask. Add G from the burette into the conical flask. At first the purple colour disappears quickly but as more G is added, the colour disappears less quickly. At the end -point, one drop of G produces a pale pink colour that does not disappear on swirling. Record your titration results in the space provided on page 3 , repeating the titration as many times as you consider necessary to achieve consistent results. Show clearly how you obtain an average volume of G to be used in your calculations.

3 AMKSS 4E Prelim Exam 6092/03/2024 [Turn Over Results: [5] (b) From your titration results, obtain an average volume of solution G used. Show clearly how you obtained this volume. Average volume of G required is …………………………….. [1] (c) H is 0.0800 mol/dm3 iron(II) ions solution. Calculate the number of moles of iron(II) ions present in the volume of H used. number of moles of iron(II) ions …………………………… [1]

4 AMKSS 4E Prelim Exam 6092/03/2024 (d) Using your answer from (c), calculate the number of moles of manganate(VII) ions present in 1 dm3 of G required. [Five moles of iron(II) ions react with one mole of manganate(VII) ions.] number of moles of manganate(VII) ions in 1 dm3 of G ……………………….. [2] (e) Using your answer from (d), calculate the number of moles of manganate(VII) ions in 250 cm3 of G. number of moles of manganate(VII) ions in 250 cm3 of G ………………………… [1] (f) Using your answer from (e), calculate the mass of manganese in the 2.12 g sample of mangalloy. [Ar: Mn, 55] mass of manganese in 2.12 g of mangalloy ……………………………… [1] (g) Using your answer from (f), calculate the percentage by mass of manganese in mangalloy. percentage by mass of manganese in mangalloy: ………………………….% [1]

5 AMKSS 4E Prelim Exam 6092/03/2024 [Turn Over (h) A student repeated the experiment and accidentally used a 20.0 cm 3 pipette to measure solution H into the flask for each titration. The student thought that he has used a 25.0 cm3 pipette. Describe the effect it would have on the percentage by mass of manganese in the mangalloy calculated by the student. …………………………………………………………………………………......................... …………………………………………………………………………………......................... …………………………………………………………………………………......................... [1] [Total: 13]

6 AMKSS 4E Prelim Exam 6092/03/2024 2 Reactions between acids and alkali are exothermic. You are going to determine the concentration of sodium hydroxide by measuring the highest temperature change when hydrochloric acid is added to aqueous sodium hydroxide. Read all the instructions below carefully before starting the experiment in Question 2. Instructions P is 1.00 mol/dm3 of hydrochloric acid. Q is aqueous sodium hydroxide of unknown concentration. (a) Put Q into a burette. Place Styrofoam cup into a beaker. Using a measuring cylinder, measure 25.0 cm3 of P into a Styrofoam cup. Measure the temperature of the solution and record in the table below. Add 5.00 cm 3 of Q to solution P, stirring with the thermometer. Measure the highest temperature of the mixture and record your results in the table below. Continue to add 5.00 cm 3 of Q to the Styrofoam cup, stirring with the thermometer until a total volume of 40.00 cm 3 of Q has been added. Measure and record the highest temperature reached after each addition of 5.00 cm3 of Q in Table 1.

7 AMKSS 4E Prelim Exam 6092/03/2024 [Turn Over Table 1 total volume of Q added /cm3 highest temperature reached/°C 0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 [2]

8 AMKSS 4E Prelim Exam 6092/03/2024 (b) Use the results you have obtained to plot a graph of highest temperature reached against total volume of Q added. Draw two straight lines of best fit. The lines should cross each other.

9 AMKSS 4E Prelim Exam 6092/03/2024 [Turn Over [3] (c) Describe and explain the trend shown by your graph in (b). …………………………………………………………………………………........................... …………………………………………………………………………………........................... [2] (d) Show clearly on the graph how you obtained the volume of Q needed to for complete neutralisation of 25.0 cm3 of P. volume of Q required for complete neutralisation = ………………………............... cm3 [1] (e) Identify one key source of experimental error and explain how it affects the results. …………………………………………………………………………………........................... …………………………………………………………………………………........................... [2] [Total: 10]

10 AMKSS 4E Prelim Exam 6092/03/2024 3 You are provided with a sample of solid mixture, R. R contains two cations and one anion. Read all the instructions below carefully before starting the experiment in Question 3. Instructions Carry out the following tests. You should test and identify any gases evolved. Record your observations in the table. The volumes given below, unless instructed otherwise, are approximate and should be estimated rather than measured. tests observations (a) Transfer approximately one third of solid R into a dry hard glass test-tube. Heat the sample strongly until no further changes are seen. Leave this test -tube to stand in the test-tube rack for a few minute