Chemistry 0620/52 October/November 2023: question paper and mark scheme

Question

You are going to investigate the temperature change when aqueous sodium hydroxide neutralises dilute hydrochloric acid. The equation for the reaction is shown. NaOH + HCl → NaCl + H2O Read all of the instructions carefully before starting the experiments. Instructions You are going to do six experiments. Experiment 1 ● Fill a burette with dilute hydrochloric acid. Label this burette hydrochloric acid. ● Run some of the dilute hydrochloric acid out of the burette so that the level of the dilute hydrochloric acid is on the burette scale. ● Fill a second burette with aqueous sodium hydroxide. Label this burette sodium hydroxide. ● Run some of the aqueous sodium hydroxide out of the burette so that the level of the aqueous sodium hydroxide is on the burette scale. ● un 1.0 cm3 of dilute hydrochloric acid from the burette into the boiling tube. R ● un 9.0 cm3 of aqueous sodium hydroxide from the second burette into the same boiling tube. R ● Stir the mixture with the thermometer. Measure the highest temperature reached and record it in Table 1.1. ● Measure the pH of the mixture in the boiling tube. Record the pH in Table 1.1. ● Rinse out the boiling tube with distilled water. Experiment 2 ● Run 2.0 cm3 of dilute hydrochloric acid from the burette into the boiling tube. ● un 8.0 cm3 of aqueous sodium hydroxide from the second burette into the same boiling tube. R ● Stir the mixture with the thermometer. Measure the highest temperature reached and record it in Table 1.1. ● Measure the pH of the mixture in the boiling tube. Record the pH in Table 1.1. ● Rinse out the boiling tube with distilled water. Experiment 3 ● Repeat Experiment 2 using 3.0 cm3 of dilute hydrochloric acid and 7.0 cm3 of aqueous sodium hydroxide. Experiment 4 ● Repeat Experiment 2 using 6.0 cm3 of dilute hydrochloric acid and 4.0 cm3 of aqueous sodium hydroxide. Experiment 5 ● Repeat Experiment 2 using 7.0 cm3 of dilute hydrochloric acid and 3.0 cm3 of aqueous sodium hydroxide. Experiment 6 ● Repeat Experiment 2 using 8.0 cm3 of dilute hydrochloric acid and 2.0 cm3 of aqueous sodium hydroxide. (a) Complete Table 1.1. Table 1.1 experiment 1 2 3 4 5 6 volume of dilute hydrochloric acid / cm3 1.0 2.0 3.0 6.0 7.0 8.0 volume of aqueous sodium hydroxide / cm3 highest temperature reached / °C pH [4] (b) Add a suitable scale to the y-axis in Fig. 1.1. Your scale should extend by at least 2 °C above your highest temperature in Table 1.1. Plot your results from Experiments 1 to 6 on the grid. Draw two straight lines through your points, one through the first three points and one through the last three points. Extend your straight lines so that they cross. highest temperature reached / C 1 2 3 4 5 6 7 8 volume of dilute hydrochloric acid / cm3 Fig. 1.1 [5] (c) The point on the graph where the two straight lines cross is where all of the aqueous sodium hydroxide reacts with all of the dilute hydrochloric acid to form a neutral solution. (i) Use your graph in Fig. 1.1 to deduce the volume of dilute hydrochloric acid and the volume of aqueous sodium hydroxide that react together to produce a neutral solution. Show your working on Fig. 1.1. volume of dilute hydrochloric acid = …… cm3 volume of aqueous sodium hydroxide = …… cm3 [3] (ii) Predict the pH of the solution in the boiling tube when the volumes in (c)(i) are mixed together. pH = …… [1] (iii) Deduce which solution, dilute hydrochloric acid or aqueous sodium hydroxide, is the most concentrated. Use your answer to (c)(i) to explain why. most concentrated solution . …… explanation …… . …… [1] (d) State how the pH and temperature recorded in each experiment would differ, if at all, if a polystyrene cup is used in place of the boiling tube. Explain any differences. pH …… temperature …… explanation …… . …… [3] (e) The volumes of the solutions used in these experiments were measured using a burette. Explain why a volumetric pipette could not be used instead of a burette in this experiment. . …… [1] [Total: 18]

Question

You are provided with two substances: solid K and solid L. Do the following tests on the substances, recording all of your observations at each stage. Tests on solid K Transfer solid K to a boiling tube. Add about 10 cm3 of distilled water to the boiling tube containing solid K. Place a stopper in the boiling tube and shake the tube to dissolve solid K and form solution K. Divide solution K into three approximately equal portions in three test-tubes. (a) To the first portion of solution K, add aqueous sodium hydroxide dropwise and then in excess. Record your observations. . …… . …… [2] (b) (i) Identify two cations that the result in (a) shows could be in solid K. . …… . …… [2] (ii) Describe an additional test that could be carried out on solution K to confirm which of the two cations you have identified in (b)(i) is in solid K. You do not need to carry out this test. . …… . …… [1] (c) To the second portion of solution K, add a few drops of acidified aqueous potassium manganate(VII). Record your observations. . …… . …… [1] (d) To the third portion of solution K, add about 1 cm depth of dilute nitric acid followed by a few drops of aqueous silver nitrate. Record your observations. . …… . …… [1] (e) Identify the anion in solid K. . …… [1] Tests on solid L (f) Carry out a flame test on solid L. Record your observations. . …… [1] Divide the remaining solid L into two approximately equal portions in one hard-glass test-tube and one boiling tube. (g) Heat the first portion of solid L in the hard-glass test-tube very strongly using a roaring Bunsen flame. Test and identify any gas produced. Record your observations. . …… . …… identity of gas …… [3] (h) To the second portion of solid L in the boiling tube, add about 2 cm depth of aqueous sodium hydroxide and a piece of aluminium foil. Heat the mixture gently. Test any gas produced. . …… . …… [2] (i) Identify solid L. . …… . …… [2] [Total: 16]

Question

The solubility of solid sodium sulfate in water changes as the temperature of the water changes. Plan an experiment to find out how the solubility of sodium sulfate in water changes with temperature. You are provided with sodium sulfate, 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