ADSS Prelim P3

This question paper consists of 13 printed pages including this cover page. ADMIRALTY SECONDARY SCHOOL SUBJECT : Chemistry CODE/PAPER : 6092/3 LEVEL/STREAM : Secondary 4 Express DATE : 19 August 2024 TIME : 0800h – 0950h DURATION : 1 hour 50 minutes Instructions to candidates: Write your name, index number and class on the cover page. Write in dark blue or black pen. 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 space provided. Candidates are reminded that all quantitative answers should include appropriate units. The use of an approved scientific calculator is expected, where appropriate. The number of marks is given in brackets [ ] at the end of each question or part question. If the degree of accuracy is not specified in the question and if the answer is not exact, give the answer to three significant figures. Give answers in degrees to one decimal place. At the end of the examination, fasten all your work securely together. Chemistry practical notes for this paper are printed on Page 13. DO NOT TURN OVER THIS PAPER UNTIL YOU ARE TOLD TO DO SO. PRELIMINARY EXAMINATION 2024 For Examiner’s Use Paper 3 / 40 NAME: NO: CLASS:

2 1 The reaction of aqueous solutions of alkalis and strong acids is exothermic. H+(aq) + OH–(aq) → H2O(l) You are going to investigate how the temperature changes when different volumes of sulfuric acid and sodium hydroxide are mixed together. Read all the instructions below carefully before starting the experiments in Question 1. Instructions You are going to carry out seven experiments. P is sulfuric acid of unknown concentration. Q is a 1.20 mol/dm3 of sodium hydroxide. (a) Experiment 1  Place a polystyrene (Styrofoam) cup into a 250 cm3 glass beaker.  Put P into a burette and measure 40.00 cm3 of P into the Styrofoam cup. Measure the temperature of P and record the value in the results table provided on page 4.  Use a measuring cylinder to measure 10 cm3 of Q. Pour this volume of Q into the Styrofoam cup containing P. Stir, using the thermometer, and measure the highest temperature reached. Record this temperature in the results table provided on page 4.  Empty the polystyrene cup and rinse it with water. Experiment 2  Place a polystyrene cup into a 250 cm3 glass beaker.  Put P into a burette and measure 35.00 cm3 of P into the Styrofoam cup. Measure the temperature of P and record the value in the results table provided on page 4.  Use a measuring cylinder to measure 15 cm3 of Q. Pour this volume of Q into the Styrofoam cup containing P to make the total volume of the mixture 50 cm3. Stir, using the thermometer, and measure the highest temperature reached. Record this temperature in the results table provided on page 4.  Empty the polystyrene cup and rinse it with water. Experiments 3 to 7  Choose 5 further volumes of P between 10.00 cm3 and 40.00 cm3. Record the volumes you have chosen in the results table provided on page 4.

3  Follow the instructions for Experiment 2 for each pair of volumes you have chosen.  Complete the results table provided on page 4 by calculating the temperature rise for each experiment. (Continued on the next page)

4 Results experiment volume of P /cm3 volume of Q /cm3 initial temperature of P /°C highest temperature of mixture /°C temperature rise /°C 1 40.00 10 29.5 32.5 0.5M P 2 35.00 15 29.5 33.0 1.2M Q 3 35 15 29.5 34.0 4 30 20 29.0 36.0 5 25 25 29.0 37.0 6 20 30 29.0 35.5 7 15 35 29.0 34.5 [5]

5 (b) Use your results to plot a graph of temperature rise against volume of Q on the grid below. Use these points to draw two intersecting straight lines of best fit. You should include the origin (0, 0). [4] (c) Use your graph to determine the volume of Q used at the maximum rise in temperature. volume of Q used = ……..……………. cm3 [1] (d) Calculate the volume of P required to neutralise the volume of Q in (c). volume P used = ……..……………. cm3 [1] (e) Hence or otherwise, calculate the concentration of P. F concentration of P = ……..……………. mol/dm3 [3]

6 (f) Explain why the mixture was conducted in a polystyrene cup instead of a glass beaker. ………………………………………………………………………………………….. ………………………………………………………………………………………….. [1] (g) The experiment was repeated using 20 cm3 of P with concentration of 2 mol/dm3. It was discovered that only 15 cm3 of Q was required to reach the maximum temperature. Predict whether the maximum temperature reached will be higher, lower or equal to the maximum temperature obtained in the experiment that you conducted. Explain your answer. ………………………………………………………………………………………….. ………………………………………………………………………………………….. ………………………………………………………………………………………….. [2]

7 2 Copper(II) carbonate decomposes on heating. CuCO3(s) → CuO(s) + CO2(g) You are supplied with an impure sample of copper(II) carbonate. You are to determine the percentage by mass of copper(II) carbonate present in the sample. Read all the instructions carefully before starting the experiment in Question 2. Instructions C is impure copper(II) carbonate. (a)  Weigh the empty boiling tube and record the mass.  Carefully add 2.0 g of C to the boiling tube.  Weigh the boiling tube and its contents and record the mass.  Gently heat the boiling tube and its contents for 1 minute so that the copper(II) carbonate decomposes.  Leave the boiling tube and its contents to cool to room temperature.  Reweigh the boiling tube and its contents and record the mass.  Record all your results in an appropriate format. Results [2] (b) From your results, deduce the change in mass of C after thermal decomposition has taken place. change in mass of C = ……..……………. g [1]

8 (c) Calculate the mass of copper(II) carbonate that has reacted. [Ar: C, 12; Cu, 64; O, 16] mass of copper(II) carbonate = ……..……………. g [2] (d) Calculate the percentage by mass of copper(II) carbonate in C. percentage by mass of copper(II) carbonate in C = ……..……………. % [1] (e) Suggest one way to improve the accuracy of the experiment. ………………………………………………………………………………………….. ………………………………………………………………………………………….. ………………………………………………………………………………………….. [1]

9 3 Hard water is water that has a high concentration of dissolved minerals. It contains one cation and one anion from those listed in the Qualitative Analysis notes. Hard water can be softened by adding a certain compound to remove the dissolved cations from the hard water. X is a sample of hard water. Y contains a compound that can soften hard water. You will carry out tests on X and Y to identify the ions present. Instructions (a) (i) Carry out the following tests. 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. test instructions observations 1 Put about 1 cm depth of solution X into a test-tube. Add aqueous sodium hydroxide slowly with shaking until no further change is seen. Keep this mixture for Test 4. 2 Put about 1 cm depth of solution X into a test-tube. Add aqueous ammonia slowly with shaking until no further change is seen. 3 Put about 1 cm depth of solution X into a test-tube. Add an equal depth of dilute nitric acid and then add