Chemistry 0620/62 February/March 2021: question paper and mark scheme

Question

Silver chloride is an ionic compound and is insoluble in water. Molten silver chloride breaks down during electrolysis. The products are chlorine and silver. Chlorine gas is soluble in water and toxic. A student suggests using the apparatus shown to break down silver chloride. power supply silver chloride (a) Draw an arrow on the diagram to show where heat must be applied so that the silver chloride can break down. [1] (b) Complete the diagram to show how chlorine gas can be collected and the volume of the chlorine measured. Label any apparatus you have drawn. [2] (c) Give two observations that are made as the silver chloride breaks down. 1 . …… 2 . …… [2] (d) The person doing the experiment followed all normal laboratory safety rules. State one additional safety precaution that should be taken when doing this experiment. Give a reason for your answer. safety precaution …… reason . …… [2] (e) Suggest one reason why zinc is not a suitable material to use as the electrodes. . …… . …… [1] (f) The chlorine gas was bubbled into an aqueous solution of a sodium salt. The colour of the solution changed from colourless to orange. Identify the sodium salt and explain what has happened to cause the colour change. sodium salt …… explanation…… . …… [2] [Total: 10]

Question

A student investigated the reaction between aqueous potassium hydroxide and two different aqueous solutions of hydrochloric acid labelled solution A and solution B. Two experiments were done. (a) Experiment 1 ● A burette was filled with solution A. Some of solution A was run out of the burette so that the level of solution A was on the burette scale. ● A measuring cylinder was used to measure 25 cm3 of the aqueous potassium hydroxide. ● The aqueous potassium hydroxide was poured into a conical flask. ● Five drops of methyl orange indicator were added to the conical flask. ● Solution A was added slowly from the burette to the conical flask, while the flask was swirled, until the solution just changed colour. Use the burette diagrams to complete the table for Experiment 1. 7 16 8 17 9 18 initial reading final reading Experiment 1 final burette reading / cm3 initial burette reading / cm3 volume of solution A added / cm3 Experiment 2 ● The conical flask was emptied and rinsed with distilled water. ● The burette was emptied and rinsed with distilled water. ● The burette was rinsed with solution B. ● The burette was filled with solution B. Some of solution B was run out of the burette so that the level of solution B was on the burette scale. ● A measuring cylinder was used to measure 25 cm3 of the aqueous potassium hydroxide. ● The aqueous potassium hydroxide was poured into the conical flask. ● Five drops of methyl orange indicator were added to the conical flask. ● Solution B was added slowly from the burette to the conical flask, while the flask was swirled, until the solution just changed colour. Use the burette diagrams to complete the table for Experiment 2. 7 26 8 27 9 28 initial reading final reading 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) 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] (d) (i) Deduce which aqueous solution of hydrochloric acid, A or B, was more concentrated. Explain your answer. . …… . …… [1] (ii) Deduce how many times more concentrated this solution of hydrochloric acid was than the other solution of hydrochloric acid. . …… [1] (e) Explain why Experiment 1 and Experiment 2 should be repeated. . …… . …… [1] (f) Deduce the volume of solution B required if Experiment 2 is carried out with 50 cm3 of aqueous potassium hydroxide. . …… . …… [2] (g) Describe one change that could be made to the apparatus to improve the accuracy of the results. . …… . …… [1] (h) Describe what effect using a larger conical flask would have on the results obtained. . …… [1] [Total: 15]

Question

Two solids, solid C and solid D, were analysed. Tests were done on each solid. tests on solid C Tests were carried out and the following observations were made. tests observations test 1 A flame test was carried out on solid C. a red flame was seen Solid C was dissolved in distilled water to produce solution C. test 2 About 5 cm3 of aqueous sodium hydroxide was no change added to solution C. test 3 A piece of aluminium foil was added to the effervescence was seen; mixture formed in test 2.The mixture was damp red litmus paper turned blue warmed gently and any gas produced was tested. (a) Name the gas that turned the damp red litmus paper blue in test 3. . …… [1] (b) Identify solid C. . …… . …… [2] tests on solid D Solid D was aluminium sulfate. Complete the expected observations. Solid D was dissolved in water to form solution D. Solution D was divided into four approximately equal portions in four test-tubes. (c) Aqueous sodium hydroxide was added dropwise and then in excess to the first portion of solution D. observations …… . …… [2] (d) Aqueous ammonia was added dropwise and then in excess to the second portion of solution D. observations …… . …… [2] (e) About 1 cm3 of dilute nitric acid and a few drops of aqueous silver nitrate were added to the third portion of solution D. observations …… [1] (f) About 1 cm3 of dilute nitric acid and a few drops of aqueous barium nitrate were added to the fourth portion of solution D. observations …… [1] [Total: 9]

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]