Chemistry 0620/51 October/November 2021: question paper and mark scheme

Question

You are going to investigate the temperature change when zinc reacts with two different aqueous solutions of copper(II) sulfate, solution Q and solution R. Read all of the instructions carefully before starting the experiments. Instructions You are going to do two experiments. (a) Experiment 1 ● Place a polystyrene cup into a 250 cm3 beaker for support. ● Use a measuring cylinder to pour 25 cm3 of solution Q into the polystyrene cup. ● Use a thermometer to measure the initial temperature of solution Q. Record this in the space above the table. ● Add 3 g of zinc powder to the polystyrene cup. At the same time start a stop‑watch. ● Using the thermometer, continually stir the mixture in the polystyrene cup. Record the temperature every 30 seconds for 240 seconds. Record the temperatures in the table. initial temperature = …… °C time / s 30 60 90 120 150 180 210 240 temperature / °C temperature change / °C ● Complete the table by calculating the temperature changes from the initial temperature using the equation: temperature change = temperature – initial temperature [3] (b) Experiment 2 ● Empty the polystyrene cup and rinse with distilled water. ● Repeat Experiment 1 using solution R in place of solution Q. ● Complete the table by calculating the temperature changes from the initial temperature. initial temperature = …… °C time / s 30 60 90 120 150 180 210 240 temperature / °C temperature change / °C [3] (c) Complete a suitable scale on the y-axis and plot your results from Experiment 1 and Experiment 2 on the grid. Draw two curves of best fit. Both curves must start at (0,0). Label your curves. temperature change / C 0 0 50 100 150 200 250 time / s [5] (d) From your graph, deduce the temperature change at 110 seconds in Experiment 1. Show clearly on the grid how you worked out your answer. …… °C [2] (e) Predict the temperature of the solution in Experiment 2 after 5 hours. Explain your answer. . …… . …… [2] (f) (i) Suggest why the experiments were done in a polystyrene cup rather than a glass beaker. . …… [1] (ii) Describe how the results would be different if a glass beaker is used in place of the polystyrene cup. . …… [1] (g) Suggest one change that could be made to the apparatus that would improve the accuracy of the results. Explain why this change would improve the accuracy of the results. change . …… explanation …… . …… [2] [Total: 19]

Question

You are provided with solid S and solid T. Do the following tests on the substances, recording all of your observations at each stage. tests on solid S (a) To solid S in the boiling tube, add about 10 cm3 of dilute hydrochloric acid. Test any gas produced. Keep the product for (b). Record your observations. . …… . …… [2] (b) The solution formed in (a) is solution U. Decant about 1 cm depth of solution U into a test‑tube. To solution U add aqueous sodium hydroxide dropwise and then in excess. Record your observations. . …… . …… [2] (c) Identify solid S. . …… . …… [2] tests on solid T (d) To solid T in the boiling tube, add about 10 cm3 of distilled water. Place a stopper in the boiling tube and shake the tube to dissolve solid T and form solution T. Divide solution T into four approximately equal portions in four test-tubes. (i) To the first portion of solution T, add aqueous sodium hydroxide dropwise and then in excess. Record your observations. . …… . …… [2] (ii) Pour the second portion of solution T into the test‑tube containing sodium carbonate. Record your observations. . …… . …… [2] (iii) To the third portion of solution T, add a 2 cm length of magnesium ribbon. Record your observations. . …… [2] (iv) To the fourth portion of solution T, add 1 cm depth of dilute nitric acid followed by a few drops of aqueous silver nitrate. Leave the mixture to stand for 5 minutes. Record your observations. . …… [1] (e) Identify solid T. . …… . …… [2] [Total: 15]

Question

Catalysts are substances which increase the rate of a reaction but are unchanged at the end of the reaction. Aqueous hydrogen peroxide decomposes slowly to form water and oxygen. 2H2O2(aq) → 2H2O(l) + O2(g) Copper(II) oxide is an insoluble solid. Plan an investigation to find out if copper(II) oxide is a catalyst for the decomposition of hydrogen peroxide. You must include how your results will tell you if copper(II) oxide is a catalyst. You have access to copper(II) oxide, aqueous hydrogen peroxide and all normal 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