Chemistry 0620/52 February/March 2020: question paper and mark scheme

Question

You are going to investigate the time taken to collect 40 cm3 of hydrogen gas when magnesium reacts with dilute sulfuric acid. Read all of the instructions carefully before starting the experiments. Instructions You are going to do five experiments using the apparatus shown. inverted 50 cm3 measuring cylinder dilute sulfuric acid and distilled water water Experiment 1 ●● Use the 10 cm3 measuring cylinder to pour 8 cm3 of dilute sulfuric acid into the boiling tube. ●● Use the 25 cm3 measuring cylinder to pour 12 cm3 of distilled water into the boiling tube. ●● Set up the apparatus as shown in the diagram, ensuring the inverted measuring cylinder is full of water. ●● Remove the bung from the boiling tube. ●● Add a coiled length of magnesium ribbon to the boiling tube, immediately replace the bung and start the timer. ●● Measure the time taken for 40 cm3 of gas to be collected. Record the time to the nearest second in the table in (b). ●● Feel the outside of the boiling tube. (a) (i) What happens to the temperature of the contents of the boiling tube during the reaction? . …… [1] (ii) What does your answer to (a)(i) tell you about the type of reaction? . …… [1] (iii) Describe one change that could be made to the apparatus to help keep the temperature of the contents of the boiling tube constant during the reaction. . …… [1] Experiment 2 ●● Rinse out the boiling tube with distilled water. ●● Use a measuring cylinder to pour 10 cm3 of dilute sulfuric acid and 10 cm3 of distilled water into the boiling tube. ●● Set up the apparatus as shown in the diagram, ensuring the inverted measuring cylinder is full of water. ●● Remove the bung from the boiling tube. ●● Add a coiled length of magnesium ribbon to the boiling tube, immediately replace the bung and start the timer. ●● Measure the time taken for 40 cm3 of gas to be collected. Record the time to the nearest second in the table in (b). Experiment 3 ●● Repeat Experiment 2 using the 25 cm3 measuring cylinder to pour 12 cm3 of dilute sulfuric acid into the boiling tube. Use the 10 cm3 measuring cylinder to pour 8 cm3 of distilled water into the boiling tube. Experiment 4 ●● Repeat Experiment 3 using 16 cm3 of dilute sulfuric acid and 4 cm3 of distilled water. Experiment 5 ●● Repeat Experiment 3 using 20 cm3 of dilute sulfuric acid and no distilled water. (b) Complete the table. volume of dilute volume of time to collect experiment sulfuric acid / cm3 distilled water / cm3 40 cm3 of gas / s 1 8 2 10 3 12 4 16 5 20 [4] (c) Add a suitable scale to the y-axis and plot your results from Experiments 1 to 5 on the grid. Draw a smooth line graph. time to collect 40 cm3 of gas / s 6 8 10 12 14 16 18 20 volume of dilute sulfuric acid / cm3 [4] (d) (i) From your graph, deduce the time taken to collect 40 cm3 of gas if the experiment was repeated using 9 cm3 of dilute sulfuric acid. Show clearly on the grid how you worked out your answer. …… s [2] (ii) What volume of distilled water would be needed if the experiment was repeated using 9 cm3 of dilute sulfuric acid? …… cm3 [1] (e) The rate of reaction can be calculated using the equation shown. volume of gas collected rate of reaction = time taken to collect the gas (i) Use this equation to calculate the rate of reaction in Experiment 1. Give the units for the rate of reaction you have calculated. rate of reaction = …… units = …… [2] (ii) In which Experiment, 1, 2, 3, 4 or 5, was the rate of reaction greatest? . …… [1] (f) Why would measuring the volume of dilute sulfuric acid with a burette rather than a measuring cylinder be an improvement? . …… . …… [1] (g) The magnesium starts to react with the dilute sulfuric acid as soon as it is added. (i) Why does this decrease the accuracy of the investigation? . …… . …… [1] (ii) Describe one improvement that could be made to overcome this problem. . …… . …… . …… [1] (h) Sketch on the grid in (c) the graph you would expect if all of the experiments were repeated at a higher temperature. Clearly label your graph. [1] [Total: 21] 2 You are provided with two substances, solution J and solid K. Do the following tests on solution J and solid K, recording all of your observations at each stage. tests on solution J Divide solution J into four approximately equal portions in four test‑tubes. You will need to keep one portion for the tests on solid K. (a) Describe the appearance of solution J. . …… [1] (b) Test the pH of the first portion of solution J. pH = …… [1] (c) Add a spatula measure of sodium carbonate to the second portion of solution J. Test the gas produced. Record your observations. . …… . …… . …… [3] (d) Add about 1 cm3 of dilute nitric acid and a few drops of aqueous silver nitrate to the third portion of solution J. Record your observations. . …… . …… [1] (e) Identify solution J. . …… . …… [2] tests on solid K (f) Using a spatula, place approximately half of solid K in a test‑tube. Add the fourth portion of solution J to this portion of solid K. Stopper the test-tube and shake the contents. Carefully smell the product. Record your observations. . …… [1] (g) Add the remaining solid K to about 10 cm3 of distilled water in a boiling tube. Stopper the boiling tube and shake it to dissolve solid K and form solution K. (i) Add 2 cm3 of aqueous sodium hydroxide to solution K. Record your observations. . …… [1] (ii) Warm the mixture formed in (g)(i) gently. Test any gas produced. Record your observations. . …… . …… [2] (h) Identify one ion in solid K. . …… [1] [Total: 13]

Question

In the question paper above.

Question

A black dye can be obtained from some plant roots. Plan an investigation to determine how many different coloured substances are contained in a black dye obtained from plant roots. You must include how the results you obtain will tell you how many different coloured substances are contained in the black dye. You have access to plant roots 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