Chemistry 0620/53 October/November 2025: question paper and mark scheme

Question

You are going to investigate the temperature change when a 5 cm length of coiled magnesium ribbon reacts with excess dilute sulfuric acid. Read all of the instructions carefully before starting the experiments. Instructions You are going to do five experiments. Experiment 1 • Rinse the burette with distilled water and then with dilute sulfuric acid. • Fill the burette with dilute sulfuric acid. Run some of the dilute sulfuric acid out of the burette so that the level of the dilute sulfuric acid is on the 0.0 cm3 mark. • Use the burette to add 30.0 cm3 of dilute sulfuric acid to a boiling tube. • Use the thermometer to measure the initial temperature of the acid. • Record the initial temperature in Table 1.1. • Add a coil of magnesium ribbon to the boiling tube. At the same time start the stop-watch. • Continually stir the contents of the boiling tube using the thermometer. • After 1 minute, measure the temperature of the mixture in the boiling tube. • Record this temperature in Table 1.1. Experiment 2 • Refill the burette with dilute sulfuric acid. Run some of the dilute sulfuric acid out of the burette so that the level of the dilute sulfuric acid is on the 0.0 cm3 mark. • Use the burette to add 25.0 cm3 of dilute sulfuric acid to a new boiling tube. • Use the thermometer to measure the initial temperature of the acid. • Record the initial temperature in Table 1.1. • Add a coil of magnesium ribbon to the boiling tube. At the same time start the stop-watch. • Continually stir the contents of the boiling tube using the thermometer. • After 1 minute, measure the temperature of the mixture in the boiling tube. • Record this temperature in Table 1.1. Experiment 3 • Repeat Experiment 2, using 20.0 cm3 of dilute sulfuric acid instead of 25.0 cm3. Experiment 4 • Repeat Experiment 2, using 15.0 cm3 of dilute sulfuric acid instead of 25.0 cm3. Experiment 5 • Repeat Experiment 2, using 10.0 cm3 of dilute sulfuric acid instead of 25.0 cm3. * 0000800000004 * DFD 4 (a) Complete Table 1.1. Table 1.1 volume of dilute initial temperature temperature experiment sulfuric acid temperature after 1 minute increase / cm3 / °C / °C / °C 1 2 3 4 5 [5] (b) On Fig. 1.1, complete a suitable scale on the y-axis and plot your results from Experiments 1 to 5. Draw a line of best fit. temperature increase / °C 0.0 10.0 15.0 20.0 25.0 30.0 35.0 volume of dilute sulfuric acid / cm3 Fig. 1.1 [4] * 0000800000005 * DFD 5 (c) Explain why the temperature increase changes as the volume of dilute sulfuric acid changes. …… [2] (d) Extrapolate the line of best fit on your graph in Fig. 1.1 to deduce the temperature increase if 33.0 cm3 of dilute sulfuric acid is used. Show clearly on Fig. 1.1 how you worked out your answer. temperature increase = …… [3] (e) The investigation is repeated using 2.5 cm lengths of coiled magnesium ribbon instead of 5 cm lengths. On Fig. 1.1, sketch a line to show the results you would expect. Label this line E. [1] (f) (i) Give one reason why a burette, rather than a measuring cylinder, is used to measure the volume of the dilute sulfuric acid. …… [1] (ii) Explain why the contents of the boiling tube are stirred during each experiment. …… [1] (g) Describe one change to the apparatus that will give more accurate results. Explain your answer. change to apparatus …… explanation …… [2] [Total: 19] * 0000800000006 * DFD 6

Question

You are provided with one solid: solid A. Do the following tests on solid A. Record all of your observations at each stage. Tests on solid A Add about 5 cm depth of distilled water to the boiling tube containing solid A. Replace the stopper in the boiling tube and shake the boiling tube to dissolve solid A and form solution A. Divide solution A into six approximately equal portions in four test-tubes and two boiling tubes. In (a) and (b)(i), the contents of the test-tube need to be left to stand for about 5 minutes. You should continue with the remaining parts of this question while the test-tubes in (a) and (b)(i) are standing. (a) To the first portion of solution A in a test-tube, add about 1 cm depth of aqueous sodium thiosulfate. Leave the test-tube to stand for about 5 minutes. Record your observations. …… [2] (b) (i) To the second portion of solution A in a test-tube, add about 1 cm depth of dilute sulfuric acid and then add the zinc powder. Leave the test-tube to stand for about 5 minutes. Keep the contents of the test-tube for use in (b)(ii). Record your observations. …… [2] * 0000800000007 * DFD 7 (ii) Pour the solution left in the test-tube from (b)(i) into a clean test-tube, leaving behind any solid. This is solution B. To the test-tube containing solution B, add about 4 cm depth of aqueous sodium hydroxide. Record your observations. …… [1] (c) To the third portion of solution A in a test-tube, add aqueous ammonia dropwise and then in excess. Record your observations. dropwise …… in excess …… [2] (d) To the fourth portion of solution A in a test-tube, add about 1 cm depth of dilute nitric acid followed by a few drops of aqueous barium nitrate. Record your observations. …… [1] (e) To the fifth portion of solution A in a boiling tube, add about 1 cm depth of aqueous sodium hydroxide and a small piece of aluminium foil. Gently warm the mixture and test any gas given off. Record your observations. …… [2] * 0000800000008 * DFD 8 (f) (i) To the sixth portion of solution A in a boiling tube, add about 1 cm depth of aqueous potassium iodide. Keep the product for use in (f)(ii). Record your observations. …… [1] (ii) To the product from (f)(i), add about 1 cm depth of starch solution. Keep the product for use in (f)(iii). Record your observations. …… [1] (iii) To the product from (f)(ii), add about 2 cm depth of aqueous sodium thiosulfate. Place a stopper in the boiling tube and shake the boiling tube. Record your observations. …… [1] (g) Identify the anion and the cation in solid A. …… [2] [Total: 15] * 0000800000009 * DFD 9

Question

Duralumin is an alloy containing a mixture of the metals aluminium, copper, magnesium and manganese only. Table 3.1 gives some information about the four metals in duralumin. Table 3.1 reaction with dilute reaction with dilute metal hydrochloric acid nitric acid aluminium reacts to form a soluble salt does not react reacts very slowly at room copper does not react temperature and quickly when heated to form a soluble salt reacts quickly to form a reacts quickly to form a magnesium soluble salt soluble salt reacts quickly to form a reacts quickly to form a manganese soluble salt soluble salt Plan an investigation to find the percentage by mass of aluminium in a sample of duralumin. Your plan must include how you will calculate the percentage by mass of aluminium in duralumin. You are provided with a powdered sample of the alloy duralumin, dilute hydrochloric acid, dilute nitric acid, distilled water and common laboratory apparatus. …… [6] DFD 10 * 0000800000011 * DFD 11 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 * 0000800000012 * DFD 12 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