2023 ACSI Chemistry Y4 Prelim p3

1 Anglo-Chinese School (Independent) 2023 Preliminary Examination Year 4 Express 6092/3 [Turn over Year 4 Express Preliminary Examination 2023 CHEMISTRY PAPER 3 Practical 6092/3 Thursday 31 July 2023 1 hour 50 minutes Candidates are to write their answers on the Question Paper. READ THESE INSTRUCTIONS FIRST Write your Candidate number in the space at the top of this page and on any separate answer paper used. Write in dark blue or black pen on both sides of the paper. You may use a 2B pencil for any diagrams or graphs. Do not use paper clips, glue or correction fluid. Answer all questions in all the spaces provided. The use of an approved scientific calculator is expected, where appropriate. You should show the essential steps in any calculation and record experimental results. Qualitative analysis notes are printed on page 10. 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 question paper consists of 10 printed pages. Shift Laboratory For Examiner’s Use 1 2 3 Total /40 Candidate Name : Index No. :

2 Anglo-Chinese School (Independent) 2023 Preliminary Examination Year 4 Express 6092/3 [Turn over 1 Acids of general formula HYO3 are known, where Y can be nitrogen, phosphorus, chlorine or bromine. P is a solution of one of these acids containing 3.75 g in 500 cm3. Q is 0.100 mol/dm3 sodium hydroxide. You are to identify Y by titrating Q with P. a Put solution P into the burette. Pipette a 25.0 cm3 (or 20.0 cm3) portion of Q into a flask and titrate with P using the indicator provided. Record your titration results in the space provided, repeating the titration as many times as you consider necessary to achieve consistent results. Results [5] b From your titration results, obtain an average volume of P to be used in your calculations. Show clearly how you obtained this volume. [1] Average volume of P

3 Anglo-Chinese School (Independent) 2023 Preliminary Examination Year 4 Express 6092/3 [Turn over c Q is 0.100 mol/dm3 sodium hydroxide. One mole of the acid HYO3 reacts with one mole of sodium hydroxide. Using the titration results, calculate the concentration, in mol/dm3 of the acid HYO3 present in solution P. [2] Concentration of HYO3 in P = d P is aqueous HYO3 which contains 3.75 g in 500 cm3. Using your answer to (c), calculate the relative molecular mass of HYO3. [2] Relative molecular mass of HYO3 = e Complete the table below. The relative atomic masses of hydrogen and oxygen are 1 and 16 respectively. [1] Element Relative atomic mass Formula of its acid HYO3 Relative molecular mass of its acid Bromine (Br) 80 HBrO3 Chlorine (Cl) 35.5 HClO3 Nitrogen (N) 14 HNO3 Phosphorus (P) 31 HPO3 f Using your answer to (d) and the information in the completed table to identify the element Y. [1] Y is = [Total : 12]

4 Anglo-Chinese School (Independent) 2023 Preliminary Examination Year 4 Express 6092/3 [Turn over 2 A metal ore, X in the form of an oxide contains an impurity. Carry out the following experiments on the impure solid X. Record your observations in the table. You should test and name any gas evolved. Tests on impure solid X Test No. Test Observations a Place HALF of the solid X sample in a test tube and add half a test tube of distilled water. Stir and filter the mixture: b Carry the following tests on the filtrate. (i) To a portion of the filtrate from test (a), add aqueous sodium hydroxide and warm. (ii) To a portion of the filtrate from test (a), add a few drops aqueous silver nitrate until a change is seen. Then, add aqueous ammonia until a change is seen. c Place the remaining HALF of the solid X sample in a test tube and add half a test tube of dilute nitric acid. Stir and filter the mixture: Keep the filtrate for tests c(i) and c(iii). (i) To a portion of the solution in (c), add aqueous ammonia until there is no further change.

5 Anglo-Chinese School (Independent) 2023 Preliminary Examination Year 4 Express 6092/3 [Turn over (ii) To a portion of the solution in (c), add aqueous potassium iodide and leave it to stand. Filter the mixture to better assess it. (iii) To a portion of the solution in (c), (1) add equal volume of aqueous sodium hydroxide and (2) warm the mixture. [11] d Name the metal in the ore X and the impurity it contains. [2] e (i) The ionic equation for the reaction in test c(iii)(1). [1] (ii) The chemical equation for the reaction in test c(iii)(2). [1] f Based on the observation in test c(ii), explain why a redox reaction has taken place. [2] g Suggest why dilute nitric acid is used instead of sulfuric acid or hydrochloric acid for the purpose in test (c), as a precautionary measure. [1]

6 Anglo-Chinese School (Independent) 2023 Preliminary Examination Year 4 Express 6092/3 [Turn over i Hydrogen peroxide decomposes according to the equation shown below: 2 H2O2 (aq)  2 H2O (l) + O2 (g) Solid X and manganese(IV) oxide are suitable catalysts for the decomposition reaction. Outline an experiment by which you can determine whether solid X or manganese(IV) oxide is a better catalyst. You can assume all the apparatus and regents normally found in a school laboratory are available. In your method, you should state the variables and assumptions where appropriate. You should also include a diagram and the measurements you would take and explain how you arrive at the conclusion. [4]

7 Anglo-Chinese School (Independent) 2023 Preliminary Examination Year 4 Express 6092/3 [Turn over [Total : 22]

8 Anglo-Chinese School (Independent) 2023 Preliminary Examination Year 4 Express 6092/3 [Turn over 3 A student investigated how concentration of dilute sulfuric acid affects the rate of reaction with magnesium ribbon. He carried out the following experiments by adding magnesium to excess dilute sulfuric acids of varying concentrations. His procedure was as follows: a i Using a measuring cylinder, transfer 30 cm3 of 1.0 mol/dm3 dilute sulfuric acid into a beaker. ii Add a piece of magnesium ribbon 4 cm in length to the acid and start the stopwatch at the same time. Measure the time taken for the magnesium to dissolve and record the time taken to the nearest second. iii Wash the beaker and rinse with distilled water. iv Repeat steps (i) to (iii) using 0.8, 0.6 and 0.5 mol/dm3 dilute sulfuric acid instead of 1.0 mol/dm3. Experiment Concentration of sulfuric acid / mol/dm3 Time taken for magnesium ribbon to dissolve / s 1 1.0 105 2 0.8 112 3 0.6 139 4 0.5 265 b Use the data in the table to plot the graph using the axes provided. [1] 280 240 200 160 120 80 40 0.5 0.6 0.7 0.8 0.9 1.0 Concentration of sulfuric acid, mol/dm3 Time taken for magnesium ribbon to dissolve / s

9 Anglo-Chinese School (Independent) 2023 Preliminary Examination Year 4 Express 6092/3 [Turn over c Describe the trend shown in the graph and give a conclusion for the results. [1] d Another experiment using 30 cm3 solution of 0.0210 mol sulfuric acid was carried out according to the procedure above. Using the graph in (b), predict the time taken for the 4 cm length magnesiu