SJI 2022 Y4 Prelim Chemistry 6092 Paper 3 QP

ST JOSEPH’S INSTITUTION PRELIMINARY EXAMINATION 2022 (YEAR 4) CANDIDATE NAME CLASS INDEX NUMBER CHEMISTRY Paper 3 Candidates answer on the Question Paper. No Additional Materials are required. 6092/03 30 August 2022 1 hour 50 minutes READ THESE INSTRUCTIONS FIRST Write your name, class and index number on all the work you hand in. Give details of the practical shift and laboratory where appropriate, in the boxes provided. Write in dark blue or black fluid ink pen. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, glue or correction fluid. Answer all questions in the spaces provided. The use of an approved scientif ic 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 12. The number of marks is given in brackets [ ] at the end of each question or part question. Shift Laboratory For Examiner’s Use 1 / 16 2 / 10 3 / 14 Total / 40 This document consists of 12 printed pages including this cover page.

2 1 You are going to investigate what happens when aqueous sodium hydroxide reacts with aqueous solutions of two different acids, A and B. Read all the instructions below carefully before starting the experiments in Question 1. Instructions You are going to carry out two experiments. (a) Experiment 1 Use a measuring cylinder to pour 25 cm3 of aqueous sodium hydroxide into the Styrofoam cup provided. Put the cup into a 250 cm3 beaker for support. Measure the initial temperature (Ti) of the solution and record it in the table below. Fill the burette to the 0.0 0 cm3 mark with acid A. Add 5.00 cm3 of acid A to the aqueous sodium hydroxide in the cup and stir the mixture. Measure and record the maximum temperature of the mixture in the table below. Immediately add a further 5.00 cm3 of acid A to the cup and stir the mixture. Measure and record the maximum temperature of the mixture in the table below. Continue to add 5.0 0 cm3 portions of acid A to the cup, until a total volu me of 40.00 cm3 of acid has been added. Stir after each addition and measure and record the temperatures in the table. Calculate the temperature rise for each addition by subtracting the initial temperature from the maximum temperature. At the end of this experiment, pour the mixture away and rinse the Styrofoam cup. volume of acid A added / cm3 temperature of mixture in Styrofoam cup / °C temperature rise / °C 0.00 Ti = 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 [2]

3 (b) Experiment 2 Empty the burette and rinse it with water, followed by rinsing the burette with acid B. Fill the burette to the 0.00 cm3 mark with acid B. Repeat the procedure in Experiment 1 using acid B instead of acid A. Record your results in the table below. volume of acid B added / cm3 temperature of mixture in Styrofoam cup / °C temperature rise / °C 0.00 Ti = 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 [2]

4 (c) Plot graphs o f t emperature r ise against the volume of acid added for bot h Experiments 1 and 2 on the grid . For each graph, draw two straight best-fit lines that intersect each other. Clearly label your graphs. [4]

5 (d) (i) Using the relevant graph , determine the volume of acid A required to neutralise 25 cm3 of aqueous sodium hydroxide. Show clearly on the graph how you obtained your answer. …………………….………………………………………………………………[1] (ii) Hence, calculate the concentration of aqueous sodium hydroxide given that acid A is a monobasic acid with concentration 1.00 mol/dm3. [2] (e) What type of chemical reaction, other than neutralisation, occurs when acid A reacts with sodium hydroxide? ……………………………………………………………………………………………[1] (f) In Experiment 2, why is the burette rinsed with acid B after rinsing with water? ……………………………………………………………………………………………… ……………………………………………………………………………………………[1] (g) The solutions of acids A and B are of the same concentration. In which experiment is the maximum temperature change greater? Suggest a reason for your answer. ……………………………………………………………………………………………… ……………………………………………………………………………………………[1] (h) Describe the key source of error in the experiments and suggest an improvement to reduce this source of error. ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………[2] [Total: 16]

6 2 You are provided with solid W. Read all the instructions carefully before starting the experiments in Question 2. Instructions Carry out the followi ng experiments and record all your observations in the t able. You should test and name any gas evolved. Test no. Test Observations 1 Place one spatula of solid W into a test tube. Add about 2 cm 3 of dilute hydrochloric acid to solid W. 2 Place one spatula of solid W into a test tube. Add about 5 cm 3 of aqueous copper(II) sulfate and heat the mixture gently. Leave the test tube to stand. 3 Place one spatula of solid W into a test tube. Add on e spatula of ammonium chloride to solid W and shake the test tube. Heat the mixture gently. [8]

7 What conclusions can you make about solid W? …………………….………………………………………… ...…………………… …………… ……………….…………………...……………………………………………………………..[2] [Total: 10]

8 3 When potassium chlorate(V) is heated, it decomposes and oxygen is evolved. Experiment 1 A student heats a sample of potassium chlorate( V) for three minutes. The volume of oxygen produced is measured using a gas syringe. Experiment 2 The experiment is repeated using the same mass of potassium chlorate(V) to which a small amount of copper(II) oxide is added. All other conditions are the same. The results for Experiments 1 and 2 are shown in the table below. time / s volume of oxygen collected in Experiment 1 / cm3 volume of oxygen collected in Experiment 2 / cm3 30 22 32 60 40 52 90 54 64 120 64 70 150 70 72 180 72 72

9 (a) Plot the results for both Experiments 1 and 2 on the grid below and draw a smooth curve through each set of points. La bel the curves ‘ Experiment 1 ’ and ‘Experiment 2’. [2] (b) Use your graphs to answer the following questions. (i) What is the volume of oxygen produced in Experiment 1 after 45 seconds? volume of oxygen = …………………….. [1] (ii) How much more oxygen is produced after 75 seconds in Experiment 2 than in Experiment 1? Show your working clearly. volume of oxygen = …………………….. [1] volume of oxygen collected / cm3 time / s

10 (c) Suggest the function of copper(II) oxide in Experiment 2. ..………………..…………………………………………………………………………… ………………….………………………………………………………………………..[1] (d) Why are the final two readings recorded in the table for Experiment 2 the same? ..………………..…………………………………………………………………………… ………………….………………………………………………………………………..[1] (e) The equation for the reaction is 2KClO3 → 2KCl + 3O2 By referring to the results in the table, calculate the mass of pota ssium chlorate(V) used in the experiment. [Ar: O,16; Cl, 35.5; K, 39] mass of potassium chlorate(V) = …………………….. [3]