Chemistry 0620/61 October/November 2024: question paper and mark scheme

Question

A student has a mixture of copper(II) carbonate powder and crystals of sodium sulfate. Copper(II) carbonate is insoluble in water. Sodium sulfate is soluble in water. The student tries to obtain pure copper(II) carbonate and crystals of pure sodium sulfate from the mixture. Fig. 1.1 shows four of the steps the student carries out. step 1 step 2 Add distilled water to Filter the mixture. the mixture and stir. residue filtrate step 3 step 4 Heat the filtrate from step 2 Leave the residue on the filter paper until crystals start to form. from step 2 in a warm place to dry. residue heat filter paper Fig. 1.1 (a) State what happens to the sodium sulfate in step 1. …… [1] (b) State what is removed from the filtrate in step 3. …… [1] (c) Describe what must be done after the filtrate has been heated in step 3 to obtain a larger amount of sodium sulfate crystals. …… [1] (d) (i) State what must be done to the residue before it is allowed to dry in step 4 to obtain pure copper(II) carbonate. …… [1] (ii) Identify the substance removed from the copper(II) carbonate in (d)(i). …… [1] [Total: 5]

Question

A student investigates the reaction between aqueous magnesium sulfate and aqueous barium nitrate. A precipitate of barium sulfate forms in the reaction. The student does eight experiments. Experiment 1 ● Fill a burette with aqueous magnesium sulfate. Run some of the aqueous magnesium sulfate out of the burette so that the level of the aqueous magnesium sulfate is on the burette scale. ● Fill a second burette with aqueous barium nitrate. Run some of the aqueous barium nitrate out of the burette so that the level of the aqueous barium nitrate is on the burette scale. ● Add 4.0 cm3 of aqueous magnesium sulfate from the first burette into a 10 cm3 measuring cylinder. ● Add 1.0 cm3 of aqueous barium nitrate from the second burette into the same measuring cylinder. ● Place a stopper in the top of the measuring cylinder and invert the measuring cylinder several times. ● Leave the measuring cylinder to stand for 15 minutes. ● Record the level of the precipitate on the measuring cylinder scale. ● Rinse the measuring cylinder with distilled water. Experiment 2 ● Repeat Experiment 1 using 1.5 cm3 of aqueous barium nitrate instead of 1.0 cm3. Experiment 3 ● Repeat Experiment 1 using 2.5 cm3 of aqueous barium nitrate instead of 1.0 cm3. Experiment 4 ● Repeat Experiment 1 using 3.0 cm3 of aqueous barium nitrate instead of 1.0 cm3. Experiment 5 ● Repeat Experiment 1 using 3.5 cm3 of aqueous barium nitrate instead of 1.0 cm3. Experiment 6 ● Repeat Experiment 1 using 4.5 cm3 of aqueous barium nitrate instead of 1.0 cm3. Experiment 7 ● Repeat Experiment 1 using 5.0 cm3 of aqueous barium nitrate instead of 1.0 cm3. Experiment 8 ● Repeat Experiment 1 using 5.5 cm3 of aqueous barium nitrate instead of 1.0 cm3. (a) Use the information in the description of the experiments and the measuring cylinder diagrams to complete Table 2.1. Table 2.1 experiment 1 2 3 4 5 6 7 8 volume of aqueous 4.0 magnesium sulfate / cm3 volume of aqueous 1.0 barium nitrate / cm3 cm3 cm3 cm3 cm3 cm3 cm3 cm3 cm3 10 10 10 10 10 10 10 10 9 9 9 9 9 9 9 9 8 8 8 8 8 8 8 8 7 7 7 7 7 7 7 7 measuring 6 6 6 6 6 6 6 6 cylinder diagram 5 5 5 5 5 5 5 5 4 4 4 4 4 4 4 4 3 3 3 3 3 3 3 3 solution 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 precipitate level of precipitate on the measuring 1.2 cylinder scale / cm3 [4] (b) Complete a suitable scale on the y-axis and plot the results from Experiments 1 to 8 on Fig. 2.1. Draw two straight lines of best fit through your points. The first straight line should be for the first five experiments and must be extended to pass through (0,0). The second straight line should be for the last three experiments and must be horizontal. Extend the straight lines so that they cross each other. level of precipitate on the measuring cylinder scale / cm3 0.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 volume of aqueous barium nitrate / cm3 Fig. 2.1 [5] (c) Use Fig. 2.1 to deduce the level of precipitate on the measuring cylinder scale when the experiment is repeated using 2.8 cm3 of aqueous barium nitrate. Show clearly on Fig. 2.1 how you worked out your answer. level of precipitate = …… cm3 [2] (d) The student repeats the experiment using 6.5 cm3 of aqueous barium nitrate. Predict the level of precipitate on the measuring cylinder scale. Explain your answer. prediction …… explanation …… [2] (e) Sketch on Fig. 2.1 the graph obtained if all of the experiments are repeated using aqueous barium nitrate of half the concentration used in Experiments 1 to 8. [2] (f) Suggest why the measuring cylinder is inverted several times after the aqueous barium nitrate is added. …… [1] (g) Suggest why the measuring cylinder is left to stand before the level of the precipitate is recorded. …… [1] (h) The volumes of both aqueous solutions are measured using burettes. (i) Give a reason why burettes are used rather than measuring cylinders. …… [1] (ii) Suggest why burettes are used rather than volumetric pipettes. …… [1] [Total: 19]

Question

A student tests two solids: solid T and solid U. Tests on solid T Solid T is lithium sulfite. Complete the expected observations. (a) The student carries out a flame test on solid T. observations …… [1] The student dissolves the remaining solid T in water to form solution T. The student divides solution T into two portions. (b) The student adds the first portion of solution T to a test-tube containing acidified aqueous potassium manganate(VII). State the colour change. from …… to …… [2] (c) (i) To the second portion of solution T, the student adds excess dilute nitric acid. The gas produced turns filter paper soaked in acidified aqueous potassium manganate(VII) white. Identify the gas produced. …… [1] (ii) To the solution produced in (c)(i), the student adds aqueous barium nitrate. observations …… [1] Tests on solid U Solid U contains one cation and one anion. Table 3.1 shows the tests and the student’s observations for solid U. The student dissolves solid U in distilled water to form solution U. The student then divides solution U into three portions. Table 3.1 tests observations test 1 To the first portion of solution U, add a few green precipitate drops of aqueous ammonia. test 2 To the second portion of solution U, add 1 cm3 yellow precipitate of dilute nitric acid followed by a few drops of aqueous silver nitrate. test 3 To the third portion of solution U, add 1 cm3 of the solution turns brown aqueous chlorine. (d) Identify two cations that the tests and observations in Table 3.1 show could be in solid U. …… [2] (e) Describe an additional test that the student could do to confirm which one of the two cations identified in (d) is in solid U. Give the expected result for one of the cations. test …… cation …… result …… [2] (f) Identify the anion in solid U. …… [1] [Total: 10]

Question

Beetroot is a coloured vegetable. The colour is caused by a mixture of water-soluble coloured compounds. Plan an experiment to find how many water-soluble coloured compounds there are in a beetroot. Include in your plan: ● how to extract the coloured compounds from a beetroot ● how to separate the mixture of coloured compounds ● how the results show how many coloured compounds there are in a beetroot. You are provided with a beetroot, distilled water and common laboratory apparatus. …… [6] Notes for use in qualitative analysis Tests for anions anion test test result carbonate, CO32– add dilute acid, then test for carbon effervescence, carbon dioxide dioxide gas produced chloride, Cl – acidify with dilute nitric acid, then white ppt. [in solution] add aqueous silver nitrate bromide, Br – acidify with dilute nitric acid, then cream ppt. [in solution] add aqueous silver nitrate iodide, I– acidify with dilute nitric acid, then yellow ppt. [in solution] add aqueous silver nitrate nitrate, NO3– add aqueous sodium hydroxide, ammonia produced [in solution] then aluminium foil; warm carefully sulfate, SO42– acidify with dilute nitric acid, then white ppt. [in solution] add aqueous barium nitrate sulfite, SO32– add a small volume of acidified the acidified aqueous potassium aqueous potassium manganate(VII) manganate(VII) changes colour 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 white ppt., insoluble in excess a 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 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, ppt. turns brown near surface on ppt. turns brown near surface on standing standing iron(III), Fe3+ red-brown ppt., insoluble in excess red-brown ppt., insoluble in excess zinc, Zn2+ white ppt., soluble in excess, giving white ppt., soluble in excess, giving a colourless solution a colourless solution Tests for gases gas test and test result ammonia, NH3 turns damp red litmus paper blue carbon dioxide, CO2 turns limewater milky chlorine, Cl 2 bleaches damp litmus paper hydrogen, H2 ‘pops’ with a lighted splint oxygen, O2 relights a glowing splint sulfur dioxide, SO2 turns acidified aqueous potassium manganate(VII) from purple to colourless Flame tests for metal ions metal ion flame colour lithium, Li+ red sodium, Na+ yellow potassium, K+ lilac calcium, Ca2+ orange-red barium, Ba2+ light green copper(II), Cu2+ blue-green