Chemistry 0620/52 October/November 2024: question paper and mark scheme

Question

You are going to investigate the rate of the reaction between aqueous iron(III) nitrate and aqueous sodium thiosulfate. 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 aqueous sodium thiosulfate 100 cm3 beaker 50 cm3 of aqueous iron(III) nitrate printed insert printed text Fig. 1.1 (a) Experiment 1 ● Use the 50 cm3 measuring cylinder to pour 50 cm3 of aqueous iron(III) nitrate into the 100 cm3 beaker. ● Stand the beaker on the printed text of the insert as shown in Fig. 1.1. ● Use the 25 cm3 measuring cylinder to pour 15.0 cm3 of aqueous sodium thiosulfate into the beaker. At the same time start the stop-watch. ● Stir the contents of the beaker. ● Look down from above the beaker. When the printed text on the insert becomes visible, stop the stop-watch and record the time in seconds to the nearest whole number in Table 1.1. ● Rinse the beaker with distilled water. Experiment 2 ● Use the 50 cm3 measuring cylinder to pour 50 cm3 of aqueous iron(III) nitrate into the 100 cm3 beaker. ● Stand the beaker on the printed text of the insert as shown in Fig. 1.1. ● Use the 10 cm3 measuring cylinder to pour 10.0 cm3 of aqueous sodium thiosulfate into the beaker. At the same time start the stop-watch. ● Stir the contents of the beaker. ● Look down from above the beaker. When the printed text on the insert becomes visible, stop the stop-watch and record the time in seconds to the nearest whole number in Table 1.1. ● Rinse the beaker with distilled water. Experiment 3 ● Repeat Experiment 2, using 7.0 cm3 of aqueous sodium thiosulfate instead of 10.0 cm3. Experiment 4 ● Repeat Experiment 2, using 6.0 cm3 of aqueous sodium thiosulfate instead of 10.0 cm3. Experiment 5 ● Repeat Experiment 2, using 5.0 cm3 of aqueous sodium thiosulfate instead of 10.0 cm3. Table 1.1 experiment 1 2 3 4 5 volume of aqueous sodium thiosulfate / cm3 time taken for text to become visible / s [4] (b) 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 text to become visible / s 4.0 6.0 8.0 10.0 12.0 14.0 16.0 3 volume of aqueous sodium thiosulfate / cm Fig. 1.2 [4] (c) State why the contents of the beaker are stirred after adding the aqueous sodium thiosulfate to the aqueous iron(III) nitrate. …… [1] (d) Deduce which experiment has the highest rate of reaction. …… [1] (e) Use your graph in Fig. 1.2 to predict the time taken for the text to become visible if the volume of aqueous sodium thiosulfate is 12.5 cm3. Show your working on Fig. 1.2. time = …… [3] (f) (i) Explain why it would be an improvement to measure the volumes of aqueous iron(III) nitrate in a burette rather than in a measuring cylinder. …… [1] (ii) Explain why it is not possible to use a volumetric pipette to measure the volumes of the aqueous sodium thiosulfate used in the experiments. …… [1] (iii) Describe how the reliability of the results of this investigation can be checked. …… [1] (g) Describe how the results of the experiments would change if the experiments are repeated using a narrower and taller beaker. Explain your answer. change in results …… explanation …… [2] (h) Describe additional measurements that must be taken to determine whether the reaction in this investigation is exothermic or endothermic. …… [1] [Total: 19]

Question

You are provided with two solids: solid M and solid N. Do the following tests on solid M and solid N. Record all of your observations at each stage. Tests on solid M (a) Carry out a flame test on solid M. Record your observations. …… [1] Transfer the remaining solid M to a boiling tube. Add about 5 cm depth of distilled water to solid M, place a stopper in the boiling tube and shake the boiling tube to dissolve solid M and form solution M. Divide solution M into four approximately equal portions in one boiling tube and three test-tubes. (b) To the first portion of solution M in the boiling tube, add aqueous sodium hydroxide dropwise until it is in excess. Record your observations. …… [2] (c) To the second portion of solution M in a test-tube, add the piece of magnesium ribbon. Record your observations. …… [1] (d) To the third portion of solution M in a test-tube, add about 2 cm depth of aqueous hydrogen peroxide. Record your observations. …… [2] (e) To the fourth portion of solution M in a test-tube, add about 1 cm depth of dilute nitric acid followed by a few drops of aqueous silver nitrate. Leave the mixture to stand for about two minutes. Record your observations. …… [1] (f) Identify the three ions in solid M. …… [3] Tests on solid N (g) Transfer approximately half of solid N to a boiling tube. Add about 5 cm depth of dilute sulfuric acid to the boiling tube. Test any gas produced. Record your observations. …… [2] (h) Add the remaining solid N to a boiling tube and add about 2 cm depth of distilled water. Do not place a stopper in the boiling tube. Shake the boiling tube carefully to dissolve solid N and form solution N. To solution N, add about 2 cm depth of aqueous sodium hydroxide. Gently warm the mixture and test any gas given off. Record your observations. …… [1] (i) Identify solid N. …… [2] [Total: 15]

Question

Limes and lemons are citrus fruits which contain aqueous citric acid in their juice. Citric acid reacts with alkalis such as aqueous sodium hydroxide. Plan an investigation to find which of lime juice and lemon juice contains the most concentrated aqueous citric acid. Assume that citric acid is the only acid present in the juices. Your plan must include: ● the method to use ● how the results are used to determine which juice contains the most concentrated aqueous citric acid. You are provided with lime juice, lemon juice, aqueous sodium hydroxide and common laboratory apparatus and chemicals. …… [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