Chemistry 0620/53 October/November 2023: question paper and mark scheme

Question

You are going to investigate the reaction between dilute hydrochloric acid and aqueous sodium hydroxide. Read all of the instructions carefully before starting the experiments. Instructions You are going to do two experiments. (a) Experiment 1 ● Fill a burette with aqueous sodium hydroxide. Run some of the aqueous sodium hydroxide out of the burette so that the level is on the burette scale. ● Record the initial burette reading in Table 1.1. ● Use a measuring cylinder to pour 25 cm3 of dilute hydrochloric acid into a conical flask. ● Stand the conical flask on a white tile. ● Add five drops of methyl orange indicator to the conical flask. ● Slowly add aqueous sodium hydroxide from the burette to the conical flask, while swirling the flask, until the solution just changes colour. ● Record the final burette reading in Table 1.1. Experiment 2 ● Empty the conical flask and rinse it with distilled water. ● Refill the burette with aqueous sodium hydroxide. Run some of the aqueous sodium hydroxide out of the burette so that the level is on the burette scale. ● Record the initial burette reading in Table 1.1. ● Use the measuring cylinder to pour 25 cm3 of dilute hydrochloric acid into the conical flask. ● Add 0.50 g of powdered calcium carbonate to the conical flask and swirl the flask. ● Stand the conical flask on a white tile. ● Add five drops of methyl orange indicator to the conical flask. ● Slowly add aqueous sodium hydroxide from the burette to the conical flask, while swirling the flask, until the solution just changes colour. ● Record the final burette reading in Table 1.1 and complete the table. Table 1.1 Experiment 1 Experiment 2 final burette reading / cm3 initial burette reading / cm3 volume of aqueous sodium hydroxide added / cm3 [4] (b) (i) State the colour change observed in the conical flask at the end-point in both experiments. from …… to …… [1] (ii) State the colour change observed if thymolphthalein is used in place of methyl orange. from …… to …… [1] (c) When 0.50 g of calcium carbonate is added to the conical flask in Experiment 2, a gas is produced. Suggest the identity of the gas. . …… [1] (d) In Experiment 2, the conical flask is rinsed with water but the burette is not rinsed with water. (i) State why there is no need to rinse the burette with water. . …… [1] (ii) Explain why the conical flask is rinsed with water. . …… . …… [1] (iii) The conical flask is not dried after being rinsed with water. State how drying the conical flask affects the volume of aqueous sodium hydroxide needed to reach the end-point. Explain your answer. . …… . …… . …… [2] (e) (i) Compare the volumes of aqueous sodium hydroxide needed to reach the end-point in Experiment 1 and Experiment 2. . …… . …… [2] (ii) Explain why different volumes of aqueous sodium hydroxide are needed in Experiment 1 and Experiment 2. . …… . …… [1] (iii) Calculate the volume of aqueous sodium hydroxide needed to reach the end-point if Experiment 2 is repeated using 0.25 g of calcium carbonate instead of 0.50 g. volume of aqueous sodium hydroxide = …… [2] (f) Describe how the reliability of the results obtained can be confirmed. . …… . …… [1] [Total: 17] Question 2 starts on the next page.

Question

You are provided with two substances: solid I and solution J. Do the following tests on the substances, recording all of your observations at each stage. Tests on solid I (a) Conduct a flame test on solid I. Record your observations. . …… [1] Transfer the remaining solid I to a boiling tube. Add about 10 cm3 of distilled water to the boiling tube. Place a stopper in the boiling tube and shake the tube to dissolve solid I and form solution I. Divide solution I into four approximately equal portions in two boiling tubes and two test-tubes. (b) To the first portion of solution I in a boiling tube, add a spatula full of zinc powder followed by about 5 cm depth of dilute sulfuric acid. Leave the tube to stand for one minute. Record your observations. . …… . …… . …… [2] (c) To the second portion of solution I in a boiling tube, add aqueous sodium hydroxide dropwise and then in excess. Record your observations. dropwise …… in excess . …… [2] (d) To the third portion of solution I, add about 1 cm depth of dilute nitric acid followed by a few drops of aqueous silver nitrate. Record your observations. . …… . …… [1] (e) To the fourth portion of solution I, add about 1 cm depth of dilute nitric acid followed by a few drops of aqueous barium nitrate. Leave the test-tube to stand for about one minute. Record your observations. . …… . …… [1] (f) Identify the three ions in solid I. . …… . …… . …… [3] Tests on solution J Divide solution J into three approximately equal portions in three test-tubes. (g) Test the pH of the first portion of solution J. pH = …… [1] (h) To the second portion of solution J, add the piece of magnesium ribbon. Test and identify any gas produced. Record your observations. . …… . …… identity of gas …… [3] (i) To the third portion of solution J, add about 1 cm depth of dilute nitric acid followed by a few drops of aqueous silver nitrate. Record your observations. . …… . …… [1] (j) Identify solution J. . …… . …… [2] [Total: 17]

Question

You are asked to investigate the effect of temperature on the rate of decomposition of aqueous hydrogen peroxide. Aqueous hydrogen peroxide decomposes to make oxygen gas. hydrogen peroxide → water + oxygen The reaction is very slow unless a catalyst is added to the hydrogen peroxide. Manganese(IV) oxide is a catalyst for this reaction. Plan an investigation to find how the temperature of the aqueous hydrogen peroxide affects the rate of the catalysed reaction. Your answer should include an explanation of how your results will tell you how the rate of reaction has changed. You are provided with aqueous hydrogen peroxide, manganese(IV) oxide 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