Chemistry 0620/62 February/March 2024: question paper and mark scheme

Question

Calcium carbonate is an insoluble solid. Calcium carbonate can be made by adding excess aqueous calcium chloride to aqueous sodium carbonate. CaCl 2(aq) + Na2CO3(aq) → CaCO3(s) + 2NaCl (aq) A student makes a sample of calcium carbonate. The first two steps of the method are shown in Fig. 1.1. step 1 step 2 add excess aqueous calcium chloride stir the mixture to aqueous sodium carbonate aqueous A calcium chloride stir aqueous sodium carbonate Fig. 1.1 (a) Name the item of apparatus labelled A in Fig. 1.1. . …… [1] (b) Suggest why the mixture is stirred in step 2. . …… . …… [1] (c) After step 2 the student filters the mixture to remove the solid calcium carbonate formed and collect the filtrate. Draw a labelled diagram to show the apparatus used for this filtration. [2] (d) The solid calcium carbonate obtained by filtration is not pure. (i) Identify one substance, other than water, which is mixed with the calcium carbonate and makes it impure. . …… [1] (ii) Describe how the substance you have identified in (d)(i) can be removed from the calcium carbonate. . …… . …… [1] (e) Describe a test the student can do on the filtrate obtained in (c) to show that the calcium chloride used is in excess. Give the result the student obtains if the calcium chloride is in excess. test . …… . …… result . …… . …… [2] [Total: 8]

Question

A student investigates the reaction between aqueous sodium carbonate and two different solutions of dilute hydrochloric acid, labelled A and B. The student does three experiments. Experiment 1 ● Rinse a burette with distilled water and then with dilute hydrochloric acid A. ● Rinse a conical flask with distilled water. ● Fill the burette with dilute hydrochloric acid A. Run some of the dilute hydrochloric acid out of the burette so that the level of the dilute hydrochloric acid is on the burette scale. ● Record the initial burette reading. ● Use a measuring cylinder to pour 25 cm3 of aqueous sodium carbonate into the conical flask. ● Add five drops of methyl orange indicator to the conical flask. ● Stand the conical flask on a white tile. ● Slowly add dilute hydrochloric acid A from the burette to the conical flask, while swirling the flask, until the solution becomes orange. ● Record the final burette reading. Experiment 2 ● Refill the burette with dilute hydrochloric acid A. Run some of the dilute hydrochloric acid out of the burette so that the level of the dilute hydrochloric acid is on the burette scale. ● Record the initial burette reading. ● Empty the conical flask and rinse it with distilled water. ● Use the measuring cylinder to pour 25 cm3 of aqueous sodium carbonate into the conical flask. ● Add five drops of thymolphthalein indicator to the conical flask. ● Stand the conical flask on a white tile. ● Slowly add dilute hydrochloric acid A from the burette to the conical flask, while swirling the flask, until the solution becomes colourless. ● Record the final burette reading. Experiment 3 ● Repeat Experiment 1, using dilute hydrochloric acid B instead of dilute hydrochloric acid A. (a) Use the burette diagrams in Fig. 2.1, Fig. 2.2 and Fig. 2.3 to record the readings for Experiments 1, 2 and 3 in Table 2.1 and complete Table 2.1. Experiment 1 0 25 1 26 2 27 initial reading final reading Fig. 2.1 Experiment 2 0 12 1 13 2 14 initial reading final reading Fig. 2.2 Experiment 3 0 38 1 39 2 40 initial reading final reading Fig. 2.3 Table 2.1 Experiment 1 Experiment 2 Experiment 3 final burette reading / cm3 initial burette reading / cm3 volume of dilute hydrochloric acid added / cm3 [4] (b) (i) State which solution of dilute hydrochloric acid, A or B, is the more concentrated. Explain your answer. more concentrated solution of dilute hydrochloric acid . …… explanation …… . …… [1] (ii) Deduce how many times more concentrated this solution of dilute hydrochloric acid is than the other solution of dilute hydrochloric acid. . …… . …… [1] (c) (i) Compare the volume of dilute hydrochloric acid A used in Experiment 1 to the volume of dilute hydrochloric acid A used in Experiment 2. . …… . …… . …… [2] (ii) Deduce the volume of dilute hydrochloric acid B required to reach the end-point if Experiment 3 is repeated using thymolphthalein indicator instead of methyl orange indicator. Use your answer to (c)(i) to help you. volume of dilute hydrochloric acid B = …… [2] (d) At the start of Experiment 3 the burette is rinsed with distilled water and then with dilute hydrochloric acid B. (i) Identify the substance removed from the burette when it is rinsed with distilled water at the start of Experiment 3. . …… [1] (ii) Describe how the result of the titration would change if the burette was not rinsed with dilute hydrochloric acid B after it had been rinsed with water. . …… . …… [1] (iii) Explain why the conical flask is not rinsed with aqueous sodium carbonate after it is rinsed with water. . …… . …… [1] (e) Explain why a white tile is used during the titration. . …… . …… [1] (f) Describe the effect on the result of warming the aqueous sodium carbonate used in Experiment 1 before carrying out the titration. Explain your answer. effect …… explanation …… [2] [Total: 16]

Question

A student tests two substances: solid C and solid D. Tests on solid C Solid C is ammonium iodide. The student dissolves solid C in water to form solution C. The student divides solution C into three approximately equal portions. Complete the expected observations. (a) To the first portion of solution C, the student adds about 1 cm3 of dilute nitric acid followed by a few drops of aqueous barium nitrate. observations …… . …… [1] (b) To the second portion of solution C, the student adds about 1 cm3 of dilute nitric acid followed by a few drops of aqueous silver nitrate. observations …… . …… [1] (c) (i) To the third portion of solution C, the student adds an excess of aqueous sodium hydroxide. observations …… . …… [1] (ii) The student warms the product from (c)(i) and tests any gas given off. observations …… . …… [1] Tests on solid D Table 3.1 shows the tests and the student’s observations for solid D. Table 3.1 tests observations test 1 Do a flame test on solid D. yellow coloured flame test 2 Gently heat about half of the remaining solid D. steam is given off and condensation forms at the top of the boiling tube Hold a strip of anhydrous cobalt(II) chloride the anhydrous cobalt(II) chloride paper at the mouth of the boiling tube. paper changes colour test 3 Dissolve the remaining solid D in water to form solution D. Divide solution D into three portions. To the first portion of solution D, add aqueous green precipitate which is insoluble in excess ammonia dropwise until in excess. test 4 To the second portion of solution D, add a piece green precipitate of aluminium foil and about 5 cm3 of aqueous sodium hydroxide. Heat the mixture formed and hold damp red the red litmus paper remains red litmus paper at the mouth of the boiling tube. test 5 To the third portion of solution D, add about effervescence 5 cm3 of dilute nitric acid. Bubble any gas formed through limewater. the limewater becomes milky (d) State the final colour of the cobalt(II) chloride paper in test 2. . …… [1] (e) State what ion the observations in test 4 show is not present. . …… [1] (f) Identify the gas produced in test 5. . …… [1] (g) Identify the three ions in solid D. . …… . …… . …… [3] [Total: 10]

Question

When excess dilute sulfuric acid is added to solid zinc, hydrogen gas and aqueous zinc sulfate are made. Zn(s) + H2SO4(aq) → H2(g) + ZnSO4(aq) Plan an experiment to show that copper is a catalyst for this reaction. Your plan should include how the results of the experiment will show that copper is a catalyst for this reaction. You are provided with zinc powder, dilute sulfuric acid, copper powder 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