Chemistry 0620/63 May/June 2025: question paper and mark scheme

Question

Fermentation is a process in which yeast is used to convert aqueous glucose to ethanol and carbon dioxide. Fermentation takes place at a temperature of between 25 °C and 35 °C. C6H12O6(aq) 2C2H5OH(aq) + 2CO2(g) A student uses the apparatus shown in Fig. 1.1 to make carbon dioxide by fermentation. B A aqueous glucose and yeast water-bath Fig. 1.1 (a) Name the items of apparatus labelled A and B in Fig. 1.1. A …… B …… [2] (b) Suggest why a water-bath is used. …… [1] (c) The student measures the volume of gas that is collected every 10 minutes for 90 minutes. Their results are shown in Fig. 1.2. 100 80 volume of gas 60 collected / cm3 40 20 0 0 10 20 30 40 50 60 70 80 90 time / min Fig. 1.2 Describe how the results in Fig. 1.2 show that the fermentation is not complete after 90 minutes. …… [1] (d) The student repeats the experiment using the apparatus shown in Fig. 1.3. aqueous glucose and yeast limewater water-bath Fig. 1.3 (i) State what happens to the appearance of the limewater during fermentation. …… [1] (ii) State one observation the student would make that shows that fermentation is complete. …… [1] (e) State the method the student should use to obtain ethanol from the fermentation mixture. …… [1] [Total: 7]

Question

A student investigates how the rate of reaction between dilute hydrochloric acid and aqueous sodium thiosulfate changes as the concentration of the aqueous sodium thiosulfate decreases. During the reaction, the solution slowly becomes cloudy. As the solution becomes cloudy, it becomes more difficult to see through the solution. The student does five experiments. Experiment 1 • Use a 50 cm3 measuring cylinder to pour 50 cm3 of aqueous sodium thiosulfate into a 100 cm3 beaker. • Use a 10 cm3 measuring cylinder to pour 5 cm3 of dilute hydrochloric acid into the beaker containing the aqueous sodium thiosulfate. • Immediately start a stop-watch and stir the contents of the beaker. • Stand the beaker on a printed sheet and look down from above the beaker as shown in Fig. 2.1. eye 100 cm3 beaker aqueous sodium thiosulfate and dilute hydrochloric acid mixture printed sheet printed text Fig. 2.1 • When the text on the printed sheet is not visible, stop the stop-watch and record the time to the nearest whole number of seconds. • Empty the contents of the beaker and rinse the beaker with distilled water. Experiment 2 • Repeat Experiment 1 using 40 cm3 of aqueous sodium thiosulfate instead of 50 cm3. Use the 50 cm3 measuring cylinder to add 10 cm3 of distilled water to the beaker before adding the dilute hydrochloric acid. Experiment 3 • Repeat Experiment 2 using 30 cm3 of aqueous sodium thiosulfate and 20 cm3 of distilled water. Experiment 4 • Repeat Experiment 2 using 25 cm3 of aqueous sodium thiosulfate and 25 cm3 of distilled water. Experiment 5 • Repeat Experiment 2 using 20 cm3 of aqueous sodium thiosulfate and 30 cm3 of distilled water. (a) Use the information in the description of the experiments and the stop-watch diagrams to complete Table 2.1. Table 2.1 volume of time taken volume of aqueous volume of for text dilute experiment sodium distilled stop-watch diagram to not be hydrochloric thiosulfate water / cm3 visible acid / cm3 / cm3 /s 0 seconds 1 50 0 5 45 15 minutes 30 0 2 45 15 30 0 3 45 15 30 0 4 45 15 30 0 5 45 15 30 [3] (b) Write a suitable scale on the y-axis and plot the results from Experiments 1 to 5 on Fig. 2.2. Draw a curve of best fit. time taken for text to not be visible / s 20 25 30 35 40 45 50 volume of aqueous sodium thiosulfate / cm3 Fig. 2.2 [4] (c) The relative rate of reaction in each experiment is calculated using the equation shown. 1 relative rate of reaction = time taken (i) Calculate the relative rate of reaction in Experiment 1. Do not give units for your answer. relative rate of reaction = …… [1] (ii) State in which Experiment, 1, 2, 3, 4 or 5, the relative rate of reaction was greatest. …… [1] (d) In each experiment the total volume of aqueous sodium thiosulfate and distilled water is constant. (i) Calculate the volume of distilled water needed when the volume of aqueous sodium thiosulfate is 37 cm3. volume = …… [2] (ii) From your graph in Fig. 2.2, deduce the time for the text to not be visible when the volume of aqueous sodium thiosulfate is 37 cm3. Show clearly on Fig. 2.2 how you worked out your answer. time = …… s [2] (iii) Explain why the total volume of aqueous sodium thiosulfate and distilled water is kept constant. …… [1] (e) (i) State why measuring the volume of the dilute hydrochloric acid with a burette instead of a measuring cylinder would be an improvement. …… [1] (ii) Explain why it is not possible to use a volumetric pipette to measure the volume of aqueous sodium thiosulfate in each experiment. …… [1] (f) Explain why it is important not to change the size of the beaker to a larger beaker during the investigation. …… [2] [Total: 18]

Question

A student tests two solids: solid L and solid M. Tests on solid L Solid L is hydrated aluminium chloride. The student dissolves solid L in distilled water to form solution L. Solution L is divided into four approximately equal portions. (a) To the first portion of solution L, the student adds aqueous sodium hydroxide dropwise and then in excess. observations when added dropwise …… observations in excess …… [2] (b) To the second portion of solution L, the student adds aqueous ammonia dropwise and then in excess. observations when added dropwise …… observations in excess …… [2] (c) To the third portion of solution L, the student adds about 1 cm3 of dilute nitric acid followed by a few drops of aqueous silver nitrate. observations …… …… [1] (d) To the fourth portion of solution L, the student adds about 1 cm3 of dilute nitric acid followed by a few drops of aqueous barium nitrate. observations …… …… [1] Tests on solid M Table 3.1 shows the tests and the student’s observations for solid M. Table 3.1 tests observations test 1 Do a flame test on solid M. light green coloured flame test 2 Dissolve the remaining solid M in water to form solution M. Divide solution M into three portions. To the first portion of solution M, add about no visible change 1 cm3 of aqueous sodium hydroxide. test 3 To the second portion of solution M, add effervescence is seen; about 1 cm3 of aqueous sodium hydroxide damp red litmus paper turns blue and a piece of aluminium foil. Warm the mixture and test any gas given off. test 4 To the third portion of solution M, add about white precipitate forms 1 cm3 of dilute sulfuric acid. (e) Identify the gas given off in test 3. …… [1] (f) Identify solid M. …… [2] [Total: 9]

Question

Lead(II) chloride, PbCl 2, is an insoluble salt. Solid lead(II) chloride can be made by reacting aqueous sodium chloride with aqueous lead(II) nitrate. 2NaCl (aq) + Pb(NO3)2(aq) 2NaNO3(aq) + PbCl 2(s) Describe how to make a pure, dry sample of solid lead(II) chloride. You are provided with solid sodium chloride, solid lead(II) nitrate, distilled water 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