Chemistry 0620/52 May/June 2021: question paper and mark scheme

Question

You are going to investigate the volume of gas made when sodium carbonate reacts with dilute hydrochloric acid. Read all of the instructions carefully before starting the experiments. Instructions You are going to do five experiments using the apparatus shown. rubber delivery tube clamp bung inverted 100 cm3 measuring cylinder boiling tube trough water Experiment 1 ●● Use a 25 cm3 measuring cylinder to pour 16 cm3 of dilute hydrochloric acid into a boiling tube. ●● Set up the apparatus as shown in the diagram. Ensure the inverted measuring cylinder is full of water. ●● Remove the bung from the boiling tube. ●● Add a 2.5 g sample of sodium carbonate to the boiling tube and immediately replace the bung. ●● When the volume of gas in the measuring cylinder stops changing, measure the volume of gas in the measuring cylinder. Record the volume in the table in (a). Experiment 2 ●● Repeat Experiment 1 using 14 cm3 of dilute hydrochloric acid instead of 16 cm3. Experiment 3 ●● Repeat Experiment 2 using 12 cm3 of dilute hydrochloric acid instead of 14 cm3. Experiment 4 ●● Repeat Experiment 3 using 10 cm3 of dilute hydrochloric acid instead of 12 cm3. ●● Use a 10 cm3 measuring cylinder to measure the volume of the acid. Experiment 5 ●● Repeat Experiment 4 using 6 cm3 of dilute hydrochloric acid instead of 10 cm3. (a) Complete the table. volume of dilute volume of gas experiment hydrochloric acid / cm3 collected / cm3 1 2 3 4 5 [4] (b) Write a suitable scale on the y-axis and plot your results from Experiments 1 to 5 on the grid. Draw a straight line of best fit. volume of gas collected / cm3 4 6 8 10 12 14 16 volume of dilute hydrochloric acid / cm 3 [4] (c) (i) From your graph, deduce the volume of gas that would be collected if 7 cm3 of dilute hydrochloric acid was used. Show clearly on the grid how you worked out your answer. …… cm3 [2] (ii) The volume of gas made per cm3 of dilute hydrochloric acid can be calculated using the equation shown. volume of gas collected in cm3 volume of gas per cm3 of acid = volume of acid in cm3 Use this equation and your answer to (c)(i) to calculate the volume of gas made per cm3 of dilute hydrochloric acid. …… [1] (d) The bung is removed and then replaced immediately after the sodium carbonate is added to the boiling tube. (i) Explain why the bung must be replaced immediately after the sodium carbonate is added to the boiling tube. . …… . …… [1] (ii) Explain how the apparatus could be altered so that the bung does not have to be removed. You may draw a diagram to explain your answer. . …… . …… [2] (e) State one advantage of using a burette rather than a measuring cylinder to measure the volume of the dilute hydrochloric acid. . …… [1] (f) In Experiments 1 to 5, the sodium carbonate was in excess. Sketch on the grid the graph you would expect if all of the experiments were repeated using dilute hydrochloric acid of half the concentration. Label your line F. [2] [Total: 17]

Question

You are provided with one solution, solution G, and one solid, solid H. Do the following tests on the substances, recording all of your observations at each stage. tests on solution G Divide solution G into four approximately equal portions in three test‑tubes and one boiling tube. Keep one portion in a test‑tube for use in the tests on solid H. (a) To the first portion of solution G in a test‑tube, add aqueous sodium hydroxide dropwise and then in excess. Record your observations. . …… . …… [2] (b) To the second portion of solution G in a test‑tube, add about 1 cm depth of dilute nitric acid followed by a few drops of aqueous silver nitrate. Record your observations. . …… [1] Keep the third portion of solution G for use in (i). (c) To the portion of solution G in a boiling tube, add approximately 15 cm3 of aqueous hydrogen peroxide. Test any gas produced. Record your observations. . …… . …… . …… [3] (d) Identify the gas formed in (c). . …… [1] (e) Use the results of (a) and (b) to identify solution G. . …… . …… . …… [2] tests on solid H (f) Carry out a flame test on solid H. Record your observations. . …… [1] Place solid H 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 H and form solution H. Divide solution H into three approximately equal portions in three test‑tubes. (g) To the first portion of solution H add aqueous ammonia dropwise and then in excess. Record your observations. . …… . …… . …… [3] (h) To the second portion of solution H add approximately 1 cm depth of dilute nitric acid followed by a few drops of aqueous barium nitrate. Record your observations. . …… . …… [1] (i) To the third portion of solution H add your remaining portion of solution G. Record your observations. . …… . …… [1] (j) Identify solution H. . …… . …… [2] [Total: 17]

Question

The mineral epsomite contains hydrated magnesium sulfate. When epsomite is heated strongly, it loses water and eventually becomes anhydrous magnesium sulfate. Plan an investigation to find the percentage by mass of water in a sample of epsomite. Your plan should include how you would calculate the percentage by mass of water in epsomite. You have access to 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