Chemistry 0620/52 May/June 2020: question paper and mark scheme

Question

You are going to investigate the temperature change when magnesium ribbon reacts with dilute sulfuric acid. Read all of the instructions carefully before starting the experiments. Instructions You are going to do five experiments. Experiment 1 ●● Use a measuring cylinder to pour 20 cm3 of dilute sulfuric acid into a boiling tube. ●● Use a thermometer to measure the initial temperature of the acid. Record the initial temperature in the table in (a). ●● Place a 1 cm length of magnesium ribbon into the boiling tube. ●● Continually stir the acid and magnesium ribbon in the boiling tube using a thermometer. Make sure the magnesium ribbon remains in the acid. ●● Measure the highest temperature reached by the mixture. Record the highest temperature of the mixture in the table in (a). ●● Rinse out the boiling tube with distilled water. Experiment 2 ●● Repeat Experiment 1 using a 2 cm length of magnesium ribbon instead of the 1 cm length. Experiment 3 ●● Repeat Experiment 1 using a 3 cm length of magnesium ribbon instead of the 1 cm length. Experiment 4 ●● Repeat Experiment 1 using a 5 cm length of magnesium ribbon instead of the 1 cm length. Experiment 5 ●● Repeat Experiment 1 using a 6 cm length of magnesium ribbon instead of the 1 cm length. (a) Complete the table. length of initial highest temperature experiment magnesium ribbon / cm temperature / °C temperature / °C increase / °C 1

Question

3 4 5 [4] (b) In which experiment, 1, 2, 3, 4 or 5, was the temperature increase the largest? . …… [1] (c) Add a suitable scale to the y-axis and plot your results from Experiments 1 to 5 on the grid. Draw a line of best fit, making sure that your line passes through (0,0). temperature increase / °C 0 0 1 2 3 4 5 6 length of magnesium ribbon / cm [5] (d) Explain why the graph line must pass through (0,0). . …… . …… [1] (e) From your graph, deduce the temperature increase if Experiment 1 is repeated using a 4 cm length of magnesium ribbon. Show clearly on the grid how you worked out your answer. …… °C [2] (f) (i) Why would carrying out the experiment in a polystyrene cup rather than a boiling tube improve the accuracy of the results? . …… . …… [1] (ii) Sketch on the grid the graph you would expect if the experiment was repeated using a polystyrene cup instead of a boiling tube. [1] (g) The volume of dilute sulfuric acid could be measured with a 20 cm3 pipette. (i) State one advantage of using a pipette rather than a measuring cylinder. . …… . …… [1] (ii) State one disadvantage of using a pipette rather than a measuring cylinder. . …… . …… [1] [Total: 17] 2 You are provided with two substances, solid L and solid M. Do the following tests on solid L and solid M, recording all of your observations at each stage. tests on solid L (a) Describe the appearance of solid L. . …… [1] Place solid L in a boiling tube. Add about 20 cm3 of distilled water to the boiling tube. Place a stopper in the boiling tube and shake the tube to dissolve solid L and form solution L. Divide solution L into five approximately equal portions in five test-tubes. (b) Test the pH of the first portion of solution L. pH = …… [1] (c) To the second portion of solution L add about 1 cm depth of dilute nitric acid followed by about 1 cm depth of aqueous silver nitrate. Leave the test-tube to stand for at least five minutes. Continue with the rest of the experiment while the test-tube is left to stand. Record your observations after the test-tube has been left to stand. . …… . …… [1] (d) To the third portion of solution L add approximately 5 cm3 of aqueous sodium carbonate. Record your observations. . …… . …… . …… [2] (e) To the fourth portion of solution L add aqueous sodium hydroxide slowly until it is in excess and no further changes are seen. Record your observations. . …… . …… . …… [2] (f) To the fifth portion of solution L add aqueous ammonia slowly until it is in excess and no further changes are seen. Record your observations. . …… . …… [2] (g) Identify solid L. . …… . …… [2] tests on solid M (h) Carry out a flame test on solid M. Record your observations. . …… [1] (i) Place the remaining solid M into a boiling tube. Add about 10 cm3 of dilute nitric acid to solid M in the boiling tube. Test any gas produced. Record your observations. Keep the solution formed for (j). . …… . …… . …… [2] (j) To the solution formed in (i) add about 1 cm depth of aqueous barium nitrate. Record your observations. . …… [1] (k) Identify solid M. . …… [2] [Total: 17]

Question

Many window-cleaning products contain aqueous ammonia. Aqueous ammonia is an alkali that reacts with dilute acids. Plan an investigation to find which of two window-cleaning products contains the more concentrated aqueous ammonia. Include in your plan: ●● the method you will use ●● how your results will be used to determine which window-cleaning product contains the most concentrated aqueous ammonia. You are provided with an aqueous solution of the two window‑cleaning products, dilute hydrochloric acid of known concentration 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