Chemistry 0620/51 May/June 2021: question paper and mark scheme

Question

You are going to investigate the temperature decrease when sodium hydrogencarbonate reacts with dilute hydrochloric acid. Read all of the instructions carefully before starting the experiments. Instructions You are going to do six experiments. (a) Experiment 1 ● Use a measuring cylinder to pour 25 cm3 of dilute hydrochloric acid into a conical flask. ● Use a thermometer to measure the initial temperature of the acid. Record the initial temperature in the table. ● Add the 1 g sample of sodium hydrogencarbonate to the conical flask. At the same time start the stop-clock. ● Continually stir the acid and sodium hydrogencarbonate mixture in the conical flask using the thermometer. ● Measure the temperature reached by the mixture after 1 minute. Record the temperature of the mixture in the table. ● Calculate and record the temperature decrease in the table. ● Rinse the conical flask with distilled water. Experiment 2 ● Repeat Experiment 1 using 2 g of sodium hydrogencarbonate instead of 1 g. Experiment 3 ● Repeat Experiment 1 using 3 g of sodium hydrogencarbonate instead of 1 g. Experiment 4 ● Repeat Experiment 1 using 5 g of sodium hydrogencarbonate instead of 1 g. Experiment 5 ● Repeat Experiment 1 using 6 g of sodium hydrogencarbonate instead of 1 g. Experiment 6 ● Repeat Experiment 1 using 7 g of sodium hydrogencarbonate instead of 1 g. mass of sodium initial temperature after temperature experiment hydrogencarbonate / g temperature / °C 1 minute / °C decrease / °C 1 1 2 2 3 3 4 5 5 6 6 7 [4] (b) Complete a suitable scale on the y-axis and plot your results from Experiments 1 to 6 on the grid. Draw two best-fit straight lines through your points. The first straight line should be for the first three points and must pass through (0,0). The second straight line should be for the last three points and must be horizontal. Extend your straight lines so that they meet each other. temperature decrease / °C 0 0 1 2 3 4 5 6 7 mass of sodium hydrogencarbonate / g [5] (c) (i) From your graph, determine the temperature decrease and mass of sodium hydrogencarbonate where your two straight lines meet. Include appropriate units in your answer. Show clearly on the grid how you worked out your answer. temperature decrease = …… mass of sodium hydrogencarbonate = …… [3] (ii) Explain why the temperature decrease becomes constant for high masses of sodium hydrogencarbonate. . …… . …… [1] (d) The investigation could be repeated with dilute hydrochloric acid of half the concentration, but the same volume. Sketch on the grid the graph you would expect to obtain. Label your line D.[2] (e) Suggest two changes that could be made to the apparatus that would improve the accuracy of the results. For each change explain why it would improve the accuracy of the results. change 1 . …… explanation 1 …… . …… change 2 . …… explanation 2 …… . …… [4] [Total: 19]

Question

You are provided with one solid, solid E, and one solution, solution F. Do the following tests on the substances, recording all of your observations at each stage. tests on solid E (a) Place about half of solid E in a hard-glass test-tube. Heat the solid gently for about 30 seconds. Record your observations. . …… . …… . …… [2] Transfer the remaining solid E 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 E and form solution E. Divide solution E into three approximately equal portions in two test-tubes and one boiling tube. (b) To the first portion of solution E in a test-tube, add about 1 cm depth of dilute nitric acid followed by a few drops of aqueous barium nitrate. Record your observations. . …… [1] (c) To the second portion of solution E in a test-tube, add excess aqueous ammonia. Record your observations. . …… [1] (d) To the third portion of solution E in the boiling tube, add aqueous sodium hydroxide dropwise and then in excess. Keep the product for use in (e). Record your observations. . …… . …… . …… [2] (e) Gently warm the product from (d). Test any gas produced. Record your observations. . …… . …… [1] (f) Identify the three ions contained in solid E. . …… . …… [3] tests on solution F (g) Carry out a flame test on solution F. Record your observations. . …… [1] (h) Divide the remaining solution F into two approximately equal portions in two test-tubes. (i) To the first portion of solution F add a few drops of universal indicator solution. Record your observations. . …… . …… [1] (ii) To the second portion of solution F add approximately 2 cm depth of aqueous copper(II) sulfate. Record your observations. . …… . …… [1] (i) Identify solution F. . …… . …… [2] [Total: 15]

Question

Dilute hydrochloric acid reacts with calcium carbonate to make carbon dioxide gas. The apparatus shown in the diagram can be used to follow the progress of the reaction. The carbon dioxide gas leaves the flask causing the mass shown on the balance to decrease. cotton wool dilute hydrochloric acid calcium carbonate 260.00 balance Plan an investigation, using the apparatus shown in the diagram, to find out how the temperature of the dilute hydrochloric acid affects the rate of the reaction. Your plan should include how your results will show how the temperature of the dilute hydrochloric acid affects the rate of the reaction. You are provided with dilute hydrochloric acid, calcium carbonate and common laboratory apparatus. . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… [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