Chemistry 0620/52 May/June 2023: question paper and mark scheme

Question

You are going to investigate how the rate of the reaction between aqueous iron(III) nitrate and aqueous sodium thiosulfate changes with temperature. Read all of the instructions carefully before starting the experiments. Instructions You are going to do five experiments using the apparatus shown in Fig. 1.1. eye 5 cm3 of aqueous sodium thiosulfate 100 cm3 beaker 50 cm3 of aqueous iron(III) nitrate printed insert printed text Fig. 1.1 (a) You must not heat any solution to a temperature of above 55 °C in these experiments. Experiment 1 ● Use a 50 cm3 measuring cylinder to pour 50 cm3 of aqueous iron(III) nitrate into a 100 cm3 beaker. ● Stand the beaker on the printed insert as shown in Fig. 1.1. ● Use a 10 cm3 measuring cylinder to pour 5 cm3 of aqueous sodium thiosulfate into the beaker. At the same time start a timer. ● Use a thermometer to stir the contents of the beaker. ● Look down from above the beaker. When the text on the printed insert becomes visible, stop the timer and record the time in seconds to the nearest whole number in Table 1.1. ● Use the thermometer to measure the temperature of the solution in the beaker when the text becomes visible. Record the temperature in Table 1.1. ● Rinse the beaker and thermometer with water. Experiment 2 ● Use the 50 cm3 measuring cylinder to pour 50 cm3 of aqueous iron(III) nitrate into the 100 cm3 beaker. ● Heat the beaker on a gauze over a Bunsen burner. Use the thermometer to measure the temperature of the aqueous iron(III) nitrate. Stop heating when the temperature has increased by about 5 °C. ● Stand the beaker on the printed insert. ● Use the 10 cm3 measuring cylinder to pour 5 cm3 of aqueous sodium thiosulfate into the beaker. At the same time start the timer. ● Use the thermometer to stir the contents of the beaker. ● Look down from above the beaker. When the text on the printed insert becomes visible, stop the timer and record the time in seconds to the nearest whole number in Table 1.1. ● Use the thermometer to measure the temperature of the solution when the text becomes visible. Record the temperature in Table 1.1. ● Rinse the beaker and thermometer with water. Experiment 3 ● Repeat Experiment 2, this time heating the aqueous iron(III) nitrate until the temperature has increased by about 10 °C. Experiment 4 ● Repeat Experiment 2, this time heating the aqueous iron(III) nitrate until the temperature has increased by about 15 °C. Experiment 5 ● Repeat Experiment 2, this time heating the aqueous iron(III) nitrate until the temperature has increased by about 20 °C. Table 1.1 experiment 1 2 3 4 5 time taken for the text to become visible / s temperature of the solution when the text becomes visible / °C [4] (b) State the sudden colour change seen immediately aqueous sodium thiosulfate is added to aqueous iron(III) nitrate. start colour . …… end colour . …… [1] (c) Write a suitable scale on the y-axis and plot your results from Experiments 1 to 5 on Fig. 1.2. Draw a smooth curve of best fit. time taken for the text to become visible / s 10 20 30 40 50 60 temperature of the solution when the text becomes visible / C Fig. 1.2 [4] (d) Deduce the experiment in which the rate of reaction is fastest. . …… [1] (e) Use your graph to predict the temperature of the solution when the text becomes visible after 65 seconds. Show your working on Fig. 1.2. temperature = …… °C [2] (f) Explain why wrapping the beaker in cotton wool after it has been heated will improve the accuracy of the results obtained. . …… . …… [2] (g) (i) Explain why it would be an improvement to measure the volume of aqueous iron(III) nitrate in a burette rather than a measuring cylinder. . …… . …… [1] (ii) Suggest why it would not be an improvement to add the aqueous sodium thiosulfate using a pipette. . …… . …… [1] (h) Suggest why the aqueous sodium thiosulfate must be added after the aqueous iron(III) nitrate has been heated and not before it is heated. . …… . …… [1] (i) Describe how the results of the experiment would change if the experiment is repeated using a 250 cm3 beaker instead of the 100 cm3 beaker. Explain your answer. change in results …… explanation …… . …… [2] [Total: 19]

Question

You are provided with two substances: solution F and solid G. Do the following tests on the substances, recording all of your observations at each stage. Tests on solution F (a) Carry out a flame test on solution F. Record your observations. . …… [1] Divide the remaining solution F into two approximately equal portions in one boiling tube and one test-tube. (b) (i) To the first portion of solution F in the boiling tube, add about 1 cm depth of aqueous sodium hydroxide and a piece of aluminium foil. Warm the mixture gently. Test any gas produced. Record your observations. . …… . …… [2] (ii) Identify the gas made in (i). . …… [1] (c) To the second portion of solution F, add a few drops of dilute sulfuric acid. Record your observations. . …… . …… [1] (d) Identify solution F. . …… . …… [2] Tests on solid G (e) Place about half of solid G in a hard-glass test-tube. Heat the solid gently. Record your observations. . …… . …… . …… . …… [2] (f) Place the remaining solid G in a boiling tube. Add about 10 cm3 of dilute sulfuric acid to the boiling tube. Test any gas produced. Keep the solution formed for use in (g). Record your observations. . …… . …… . …… . …… [3] (g) Leave the solution from (f) to settle for about three minutes. Carefully pour about 1 cm depth of the solution from (f) into another boiling tube. To this solution, add excess aqueous sodium hydroxide. Record your observations. . …… . …… [1] (h) Identify the ions in solid G. . …… . …… . …… [2] [Total: 15]

Question

A metal polish is a mixture of four substances. The properties of these substances are shown in Table 3.1. Table 3.1 name of substance solubility in water reaction with dilute nitric acid propanol soluble dissolves ethanoic acid soluble dissolves iron(III) oxide insoluble reacts when warmed to form a soluble salt silicon(IV) oxide insoluble no reaction Plan an experiment to find the percentage by mass of silicon(IV) oxide in the mixture. Your plan should include how you will calculate the percentage of silicon(IV) oxide in the mixture. You are provided with a sample of the metal polish, dilute nitric acid and common laboratory apparatus. . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… [6] Notes for use in qualitative analysis Tests for anions anion test test result carbonate, CO32– add dilute acid, then test for carbon effervescence, carbon dioxide dioxide gas produced chloride, Cl – acidify with dilute nitric acid, then white ppt. [in solution] add aqueous silver nitrate bromide, Br – acidify with dilute nitric acid, then cream ppt. [in solution] add aqueous silver nitrate iodide, I– acidify with dilute nitric acid, then yellow ppt. [in solution] add aqueous silver nitrate nitrate, NO3– add aqueous sodium hydroxide, ammonia produced [in solution] then aluminium foil; warm carefully sulfate, SO42– acidify with dilute nitric acid, then white ppt. [in solution] add aqueous barium nitrate sulfite, SO32– add a small volume of acidified the acidified aqueous potassium aqueous potassium manganate(VII) manganate(VII) changes colour from purple to colourless Tests for aqueous cations cation effect of aqueous sodium hydroxide effect of aqueous ammonia aluminium, Al 3+ white ppt., soluble in excess, giving white ppt., insoluble in excess a colourless solution ammonium, NH4+ ammonia produced on warming – calcium, Ca2+ white ppt., insoluble in excess no ppt. or very slight white ppt. chromium(III), Cr3+ green ppt., soluble in excess green ppt., insoluble in excess copper(II), Cu2+ light blue ppt., insoluble in excess light blue ppt., soluble in excess, giving a dark blue solution iron(II), Fe2+ green ppt., insoluble in excess, green ppt., insoluble in excess, ppt. turns brown near surface on ppt. turns brown near surface on standing standing iron(III), Fe3+ red-brown ppt., insoluble in excess red-brown ppt., insoluble in excess zinc, Zn2+ white ppt., soluble in excess, giving white ppt., soluble in excess, giving a colourless solution a colourless solution Tests for gases gas test and test result ammonia, NH3 turns damp red litmus paper blue carbon dioxide, CO2 turns limewater milky chlorine, Cl 2 bleaches damp litmus paper hydrogen, H2 ‘pops’ with a lighted splint oxygen, O2 relights a glowing splint sulfur dioxide, SO2 turns acidified aqueous potassium manganate(VII) from purple to colourless Flame tests for metal ions metal ion flame colour lithium, Li+ red sodium, Na+ yellow potassium, K+ lilac calcium, Ca2+ orange-red barium, Ba2+ light green copper(II), Cu2+ blue-green