Chemistry 0620/52 October/November 2020: question paper and mark scheme

Question

You are going to investigate the rate of the reaction between sodium metabisulfite and potassium iodate. Read all of the instructions carefully before starting the experiments. Instructions You are going to do five experiments. In each experiment the total volume of liquid is 45 cm3. Experiment 1 ●● Use a 10 cm3 measuring cylinder to pour 5 cm3 of aqueous sodium metabisulfite into the beaker. ●● Use another 10 cm3 measuring cylinder to pour 5 cm3 of starch solution into the beaker. ●● Use a 25 cm3 measuring cylinder to pour 15 cm3 of distilled water into the beaker. ●● Use another 25 cm3 measuring cylinder to pour 20 cm3 of aqueous potassium iodate into the beaker. At the same time start the stop‑clock. ●● Stir the mixture in the beaker and continue to stir until a sudden colour change is seen. ●● Stop the stop‑clock and record the time in seconds to the nearest whole number in the table. ●● Rinse the beaker with water. Experiment 2 ●● Repeat Experiment 1 using 17 cm3 of distilled water and 18 cm3 of aqueous potassium iodate. Experiment 3 ●● Repeat Experiment 1 using 21 cm3 of distilled water and 14 cm3 of aqueous potassium iodate. Experiment 4 ●● Repeat Experiment 1 using 23 cm3 of distilled water and 12 cm3 of aqueous potassium iodate. Experiment 5 ●● Repeat Experiment 1 using 25 cm3 of distilled water and 10 cm3 of aqueous potassium iodate. (a) Complete the table. experiment 1 2 3 4 5 volume of aqueous sodium metabisulfite / cm3 volume of distilled water / cm3 volume of aqueous potassium iodate / cm3 20 18 14 12 10 time taken to change colour / s [4] (b) State the sudden colour change seen. start colour . …… end colour . …… [1] (c) Add a suitable scale for the y-axis and plot your results from Experiments 1 to 5 on the grid. Draw a smooth curve of best fit. time to change colour / s 10 12 14 16 18 20 22 volume of aqueous potassium iodate / cm3 [4] (d) (i) From your graph, predict the time to change colour if 16 cm3 of aqueous potassium iodate was used. Show clearly on the grid how you worked out your answer. time to change colour = …… s [2] (ii) Calculate the volume of distilled water required if 16 cm3 of aqueous potassium iodate was used. volume of distilled water = …… cm3 [1] (e) Sketch on the grid the graph you would expect if Experiments 1 to 5 were repeated at a higher temperature. [1] (f) The concentration of potassium iodate in the reaction mixture in each experiment can be calculated using the equation shown. 0.05 × volume of aqueous potassium iodate concentration = 45 (i) Calculate the concentration of potassium iodate in the reaction mixture in Experiment 2. concentration = …… mol / dm3 [1] (ii) State which experiment, 1, 2, 3, 4 or 5, had the fastest rate of reaction. . …… [1] (g) Suggest why the volume of distilled water added to each experiment was increased as the volume of aqueous potassium iodate was decreased. . …… . …… [1] (h) Give one change you could make to the apparatus used which would improve the results. Explain your answer. change to apparatus . …… . …… explanation …… . …… [2] (i) Describe how the reliability of the results of this investigation could be checked. . …… . …… [1] [Total: 19]

Question

You are provided with two solids, solid Q and solid R. Do the following tests on solid Q and solid R, recording all of your observations at each stage. tests on solid Q (a) Using a spatula, place approximately three quarters of solid Q in a boiling tube. Add about 10 cm3 of dilute sulfuric acid to the boiling tube. Test any gas produced. Record your observations. Keep the contents of the boiling tube for (c). . …… . …… . …… [3] (b) Identify the gas given off in (a). . …… [1] (c) Filter the reaction mixture from (a). The filtrate is solution S. Pour 1 cm depth of solution S into a boiling tube. (i) To solution S in the boiling tube add aqueous sodium hydroxide dropwise and then in excess. Record your observations. . …… . …… . …… [2] (ii) Explain why it is not possible to identify the cation contained in solution S from your observations in (c)(i). . …… . …… [1] (iii) Suggest an additional test that can be done on solution S that would allow you to identify the cation contained in solution S. Do not carry out this test. . …… . …… [1] (d) Place the remaining solid Q in a hard‑glass test-tube. Heat the solid strongly until no further change is seen. Stop heating and leave the solid to cool. Record your observations. . …… . …… . …… [2] tests on solid R (e) Carry out a flame test on solid R. Record your observations. . …… [1] (f) Place solid R 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 R and form solution R. Divide solution R into two approximately equal portions in two test‑tubes. (i) Add the first portion of solution R to the aqueous bromine provided in a test‑tube. Record your observations. . …… [1] (ii) To the second portion of solution R add about 1 cm depth of dilute nitric acid followed by a few drops of aqueous silver nitrate. Record your observations. . …… . …… [1] (g) Identify solid R. . …… . …… [2] [Total: 15]

Question

Brass is a mixture of two metals, copper and zinc. Copper does not react with dilute sulfuric acid. Zinc reacts with hot dilute sulfuric acid to form the soluble salt zinc sulfate. Plan an investigation to find the percentage by mass of zinc in a sample of brass. In your answer you should include how to calculate the percentage by mass of zinc. You have access to 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