Chemistry 0620/52 February/March 2021: question paper and mark scheme

Question

You are going to investigate the reaction between aqueous potassium hydroxide and two different aqueous solutions of hydrochloric acid labelled solution A and solution B. Read all of the instructions carefully before starting the experiments. Instructions You are going to do two experiments. (a) Experiment 1 ● Fill the burette with solution A. Run some of solution A out of the burette so that the level of solution A is on the burette scale. ● Record the initial burette reading in the table. ● Use the measuring cylinder to pour 25 cm3 of aqueous potassium hydroxide into the conical flask. ● Add five drops of thymolphthalein indicator to the conical flask. ● Slowly add solution A from the burette to the conical flask, while swirling the flask, until the solution just changes colour. ● Record the final burette reading in the table and complete the table. Experiment 1 final burette reading / cm3 initial burette reading / cm3 volume of solution A added / cm3 Experiment 2 ● Empty the conical flask and rinse it with distilled water. ● Empty the burette and rinse it with distilled water. ● Rinse the burette with solution B. ● Fill the burette with solution B. Run some of solution B out of the burette so that the level of solution B is on the burette scale. ● Record the initial burette reading in the table. ● Use the measuring cylinder to pour 25 cm3 of aqueous potassium hydroxide into the conical flask. ● Add five drops of thymolphthalein indicator to the conical flask. ● Slowly add solution B from the burette to the conical flask, while swirling the flask, until the solution just changes colour. ● Record the final burette reading in the table and complete the table. Experiment 2 final burette reading / cm3 initial burette reading / cm3 volume of solution B added / cm3 [4] (b) State the colour change observed in the conical flask at the end-point in Experiment 2. from …… to …… [1] (c) State the colour change observed at the end-point if methyl orange is used as the indicator. from …… to …… [1] (d) Before starting the titration in Experiment 2 the conical flask was rinsed with water. (i) Explain why the conical flask was rinsed with water. . …… [1] (ii) The conical flask was not then rinsed with aqueous potassium hydroxide. State how rinsing the conical flask with aqueous potassium hydroxide would change the volume of solution B needed. Explain your answer. . …… . …… [2] (e) (i) Deduce which aqueous solution of hydrochloric acid, A or B, is more concentrated. Explain your answer. . …… . …… [1] (ii) Deduce how many times more concentrated this solution of hydrochloric acid is than the other solution of hydrochloric acid. . …… [1] (f) Explain why Experiment 1 and Experiment 2 should be repeated. . …… . …… [1] (g) Deduce the volume of solution B required if Experiment 2 is carried out with 50 cm3 of aqueous potassium hydroxide. . …… . …… [2] (h) Describe one change that could be made to the apparatus to improve the accuracy of the results. . …… . …… [1] (i) Describe what effect using a larger conical flask would have on the results obtained. . …… [1] [Total: 16]

Question

You are provided with two solids, solid C and solid D. Do the following tests on the substances, recording all of your observations at each stage. tests on solid C (a) Describe the appearance of solid C. . …… [1] (b) Conduct a flame test on solid C. Record your observations. . …… [1] Transfer the remaining solid C to a boiling tube. Add about 1 cm depth of distilled water to the boiling tube containing solid C. Place a stopper in the boiling tube and shake the tube to dissolve solid C and form solution C. (c) Add 5 cm3 of aqueous sodium hydroxide slowly to solution C. Keep the product for use in (d). Record your observations. . …… [1] (d) Pour about 2 cm depth of the product from (c) into a boiling tube. Add a piece of aluminium foil and warm the mixture gently. Test and identify any gas produced. Record your observations. . …… . …… identity of gas …… [3] (e) Identify solid C. . …… . …… [2] tests on solid D (f) Place solid D in 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 D and form solution D. Divide solution D into five approximately equal portions in five test-tubes. (i) To the first portion of solution D add aqueous sodium hydroxide dropwise and then in excess. Record your observations. . …… . …… [2] (ii) To the second portion of solution D add aqueous ammonia dropwise and then in excess. Record your observations. . …… . …… [2] (iii) To the third portion of solution D add about 2 cm depth of aqueous sodium carbonate. Record your observations. . …… . …… [2] (iv) To the fourth portion of solution D add about 1 cm depth of dilute nitric acid followed by a few drops of aqueous silver nitrate. Record your observations. . …… [1] (v) To the fifth portion of solution D add about 1 cm depth of dilute nitric acid followed by a few drops of aqueous barium nitrate. Record your observations. . …… [1] (g) Identify solid D. . …… . …… [2] [Total: 18]

Question

Old concrete contains calcium carbonate. Calcium carbonate reacts with dilute hydrochloric acid. CaCO3(s) + 2HCl (aq) → CaCl 2(aq) + H2O(l) + CO2(g) Plan an investigation to find which of two lumps of concrete contains the larger percentage of calcium carbonate. Your plan should include how you will use your results to determine which one of the two lumps has the larger percentage of calcium carbonate. You have access to all common laboratory materials and a supply of dilute hydrochloric acid. . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… [6] Notes for use in qualitative analysis Tests for anions anion test test result carbonate (CO32–) add dilute acid effervescence, carbon dioxide produced chloride (Cl –) acidify with dilute nitric acid, then add white ppt. [in solution] aqueous silver nitrate bromide (Br –) acidify with dilute nitric acid, then add cream ppt. [in solution] aqueous silver nitrate iodide (I–) acidify with dilute nitric acid, then add yellow ppt. [in solution] aqueous silver nitrate nitrate (NO3–) add aqueous sodium hydroxide, then ammonia produced [in solution] aluminium foil; warm carefully sulfate (SO42–) acidify, then add aqueous white ppt. [in solution] barium nitrate sulfite (SO32–) add dilute hydrochloric acid, warm sulfur dioxide produced gently and test for the presence of will turn acidified aqueous sulfur dioxide potassium manganate(VII) 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 a white ppt., insoluble in excess 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 grey-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 iron(III) (Fe3+) red-brown ppt., insoluble in excess red-brown ppt., insoluble in excess zinc (Zn2+) white ppt., soluble in excess, giving a white ppt., soluble in excess, giving a colourless solution colourless solution Tests for gases Flame tests for metal ions gas test and test result metal ion flame colour ammonia (NH3) turns damp red litmus paper blue lithium (Li+) red carbon dioxide (CO2) turns limewater milky sodium (Na+) yellow chlorine (Cl 2) bleaches damp litmus paper potassium (K+) lilac hydrogen (H2) ‘pops’ with a lighted splint copper(II) (Cu2+) blue-green oxygen (O2) relights a glowing splint sulfur dioxide (SO2) turns acidified aqueous potassium manganate(VII) from purple to colourless