Chemistry 0620/52 October/November 2021: question paper and mark scheme

Question

You are going to investigate the reaction between two different solutions of aqueous sodium carbonate, labelled solution K and solution L, and two different solutions of dilute hydrochloric acid, labelled acid M and acid N. Read all of the instructions carefully before starting the experiments. Instructions You are going to do three experiments. (a) Experiment 1 ● Fill the burette with solution K. Run some of solution K out of the burette so that the level of solution K is on the burette scale. ● Use the measuring cylinder to pour 25 cm3 of acid M into the conical flask. ● Add five drops of methyl orange indicator to the conical flask. ● Stand the conical flask on a white tile. ● Slowly add solution K from the burette to the conical flask, while swirling the flask, until the solution just changes colour. ● Record the burette readings in the table and complete the table. Experiment 1 final burette reading / cm3 initial burette reading / cm3 volume of solution K added / cm3 Experiment 2 ● Empty the conical flask and rinse it with distilled water. ● Refill the burette with solution K. Run some of solution K out of the burette so that the level of solution K is on the burette scale. ● Use the measuring cylinder to pour 25 cm3 of acid N into the conical flask. ● Add five drops of methyl orange indicator to the conical flask. ● Stand the conical flask on a white tile. ● Slowly add solution K from the burette to the conical flask, while swirling the flask, until the solution just changes colour. ● Record the burette readings in the table and complete the table. Experiment 2 final burette reading / cm3 initial burette reading / cm3 volume of solution K added / cm3 Experiment 3 ● Empty the burette and rinse it with distilled water. ● Empty the conical flask and rinse it with distilled water. ● Fill the burette with solution L. Run some of solution L out of the burette so that the level of solution L is on the burette scale. ● Use the measuring cylinder to pour 25 cm3 of acid N into the conical flask. ● Add five drops of methyl orange indicator to the conical flask. ● Stand the conical flask on a white tile. ● Slowly add solution L from the burette to the conical flask, while swirling the flask, until the solution just changes colour. ● Record the burette readings in the table and complete the table. Experiment 3 final burette reading / cm3 initial burette reading / cm3 volume of solution L added / cm3 [5] (b) State the colour change observed at the end-point in the conical flask in Experiment 1. [1] (c) Describe one other observation made when solution K is added to acid M in Experiment 1. . …… [1] (d) (i) Compare the volumes of solution K used in Experiment 1 and Experiment 2. . …… . …… [2] (ii) Suggest why different volumes of solution K were needed in Experiment 1 and Experiment 2. . …… [1] (e) Deduce the volume of solution L required to reach the end-point if Experiment 3 is repeated using acid M in place of acid N. volume of solution L = …… cm3 [1] (f) Explain why the conical flask was rinsed with water at the start of Experiment 2 and Experiment 3. . …… [1] (g) At the start of Experiment 3 the burette was rinsed with water. Describe an additional step that should have been done after rinsing the burette with water but before filling the burette with solution L. Explain your answer. . …… . …… [2] (h) Explain why the conical flask is placed on a white tile. . …… [1] (i) Describe how the reliability of the results of the experiments can be confirmed. . …… . …… [1] (j) State one source of error in Experiment 1. Suggest an improvement to reduce this error. source of error …… improvement . …… [2] [Total: 18]

Question

You are provided with solid O and liquid P. Do the following tests on the two substances, recording all of your observations at each stage. tests on solid O (a) Use a spatula to transfer approximately one third of solid O to a boiling tube. Heat the boiling tube gently and then strongly. Record your observations. . …… . …… [2] Place the remaining solid O 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 O and form solution O. Divide solution O into three approximately equal portions in one boiling tube and two test‑tubes. (b) To the first portion of solution O, in the boiling tube, add approximately 2 cm3 of aqueous sodium hydroxide. Keep the product for part (c). Record your observations. . …… [1] (c) Warm the product from (b). Test any gas produced. Record your observations. Identify the gas produced. observations …… identity of gas …… [2] (d) To the second portion of solution O 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 third portion of solution O, add the aqueous chlorine. Record your observations. . …… [1] (f) Identify solid O. . …… . …… [2] tests on liquid P (g) Add a few drops of liquid P to the test‑tube containing aqueous bromine. Replace the stopper in the test‑tube and shake the test‑tube. Record your observations. . …… . …… [2] (h) Add a few drops of liquid P to a crucible. Apply a lighted splint to the surface of liquid P in the crucible. Record your observations. . …… . …… [1] (i) To the remaining liquid P add a few drops of aqueous alkaline potassium manganate(VII). Replace the stopper in the test‑tube and shake the test‑tube. Leave the test‑tube to stand for a few minutes. Record your observations. . …… [2] (j) State what conclusions can be made about liquid P. . …… . …… [2] [Total: 16]

Question

Cobalt is a metal. Cobalt is between copper and iron in the reactivity series. The mineral spherocobaltite contains the compound cobalt(II) carbonate and no other metal ions. Cobalt(II) carbonate is insoluble in water and reacts with dilute acids to form an aqueous solution of a salt. Describe how you would obtain a sample of cobalt metal starting with a large lump of spherocobaltite. You have access to all normal laboratory apparatus and chemicals. . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… [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