Free until 14 Nov · 80% off for the first 100 · Pricing

Get started

Chemistry 9701/32 May/June 2021: question paper and mark scheme

Cambridge AS & A Level Chemistry (9701), Paper 3 (Advanced Practical Skills 2), May/June 2021. Read both free below, or download them. Done the paper? Get it marked by AI against this mark scheme.

9701_s21_qp_329701_s21_ms_329701/32/M/J/21

Mark my answers with AIRead the paper and scheme
Paper
Paper 3 (Advanced Practical Skills 2)
Total marks
40
Questions
3
Code on the paper
9701/32/M/J/21
9701_s21_ms_32.pdf

9701/32 mark scheme, question by question

Each question as it's printed, and the mark scheme's points for it, as text. Diagrams, tables and graphs are in the PDFs above.

Question 114 marks

Question

Washing soda consists of hydrated sodium carbonate, Na2CO3•10H2O. When it is stored it loses some of its water of crystallisation to leave Na2CO3•xH2O. Since water has been lost x is no longer an integer. You will carry out a titration to determine the value of x. You will titrate a solution of the sodium carbonate with hydrochloric acid. The equation for the reaction is shown. Na2CO3•xH2O(aq) + 2HCl (aq) → 2NaCl (aq) + CO2(aq) + (x+1)H2O(l) FB 1 is an aqueous solution containing 11.30 g dm–3 of Na2CO3•xH2O. FB 2 is 0.100 mol dm–3 hydrochloric acid, HCl. bromophenol blue indicator (a) Method ● Fill the burette with FB 2. ● Pipette 25.0 cm3 of FB 1 into a conical flask. ● Add a few drops of bromophenol blue indicator. ● Carry out a rough titration and record your burette readings in the space below. The rough titre is …… cm3. ● Carry out as many accurate titrations as you think necessary to obtain consistent results. ● Make sure your recorded results show the precision of your practical work. ● Record in a suitable form, in the space below, all of your burette readings and the volume of FB 2 added in each accurate titration. I II III IV V VI VII [7] (b) From your accurate titration results, obtain a value for the volume of FB 2 to be used in your calculations. Show clearly how you obtained this value. 25.0 cm3 of FB 1 required …… cm3 of FB 2. [1] (c) Calculations (i) Give your answers to (c)(ii), (c)(iii) and (c)(iv) to an appropriate number of significant figures. [1] (ii) Calculate the number of moles of hydrochloric acid present in the volume of FB 2 you calculated in (b). moles of HCl = …… mol [1] (iii) Use the equation on page 2, and your answer to (c)(ii), to calculate the concentration, in mol dm–3, of Na2CO3•xH2O present in FB 1. concentration of Na2CO3•xH2O = …… mol dm–3 [1] (iv) Calculate the value of x in this sample of Na2CO3•xH2O. Show your working. x = …… [3] [Total: 14]

Mark scheme

1(a) I Initial and final burette readings and volume added recorded for rough titre and accurate titre details tabulated. 1 (minimum 2 × 2 boxes with relevant information). II Initial and final burette readings recorded and vol of 1 FB 2 added recorded for each accurate titration. Headings and units correct for accurate titrations. Headings: initial / final and (burette) reading / volume or reading / volume at start / finish Do not allow difference / change and volume / FB 2 added / used or titre and units (cm3) or / cm3 or in cm3 or cm3 by every entry Accept vol but not V III All accurate burette readings are recorded to the nearest 0.05 cm3. 1 Do not award this mark if: 50(.00) is used as an initial burette reading; More than one final burette reading is 50(.00) Any burette reading is > 50(.00) IV The final accurate titre recorded is within 0.1 cm3 of any other accurate titre. 1 Do not award the mark if any accurate burette readings (apart from 0) are given to zero dp. For assessment of accuracy (Q) marks, the Examiner should round any burette readings to the nearest 0.05 cm3. Check and correct subtractions. Then select the ‘best’ titres using the hierarchy: • two (or more) accurate identical titres (ignoring any that are labelled ‘rough’), then • two (or more) accurate titres within 0.05 cm3, then • two (or more) accurate titres within 0.10 cm3, etc. These best titres should be used to calculate the mean titre, expressed to nearest 0.01 cm3. Calculate the difference (δ) between the candidate’s titre and the supervisor’s titre. Award the accuracy (Q) marks as shown below. 1(a) V, VI and VII 3 Award V, VI and VII for δ ⩽ 0.20 cm3 Award V and VI for 0.20cm3 < δ ⩽ 0.30 cm3 Award V for 0.30 cm3 < δ ⩽ 0.50 cm3 1(b) Candidate must average two (or more) titres that are all within 0.20 cm3. 1 Working must be shown or ticks must be put next to the two (or more) accurate titres selected. 1(c)(i) Answers to (ii) and (iii) given to 3–4 sf. 1 1(c)(ii) 0.1× vol in (b) 1 Correctly calculates moles of HCl = 1000 1(c)(iii) Correctly uses (c)(ii) ÷ 2 1 and x 40 1(c)(iv) Correctly uses 3 11.30 M1: Mr = moles from (c)(iii) M2: xH2O = Mr hydrated −106 or Mr = 106 + 18x M3: xH2O to calculate x = M2 / 18 and answer shown to 2–4 sf ALLOW alternative methods (e.g. ratio of anhydrous : water)

Question 211 marks

Question

When anhydrous sodium carbonate dissolves in water the following reaction occurs. Na2CO3(s) + aq → 2Na+(aq) + CO32–(aq) The enthalpy change for this reaction is the enthalpy change of solution of anhydrous sodium carbonate. Its value is –28.1 kJ mol–1. You will use this information to find the percentage purity of an impure sample of anhydrous sodium carbonate. FB 3 is a sample of impure anhydrous sodium carbonate. (a) Method Experiment 1 ● Weigh the cup and record the mass. ● Place between 1.9 g and 2.1 g of FB 3 in the cup. Record the mass of the cup + FB 3. ● Calculate and record the mass of FB 3 used. ● Support the cup in the beaker. ● Place 25.0 cm3 of distilled water into the measuring cylinder. Measure and record the temperature of the water. ● Place the water in the cup and stir until all the solid dissolves. ● Place the thermometer in the solution and record the highest temperature reached. Tilt the cup if necessary so that the bulb of the thermometer is fully covered. ● Rinse the cup and shake dry ready to carry out Experiment 2. Experiment 2 ● Repeat the experiment using between 3.9 g and 4.1 g of FB 3 and 25.0 cm3 of water. ● Record your results in the same way as in Experiment 1. Results I II III IV V [5] (b) Calculations (i) Use your results from Experiment 1 to calculate the heat energy, in J, released when the FB 3 dissolves. (Assume 4.2 J of heat energy changes the temperature of 1.0 cm3 of solution by 1.0 °C.) heat energy = …… J [1] (ii) Use the information on page 4 to calculate the number of moles of anhydrous sodium carbonate needed to release the amount of energy in your answer to (b)(i). moles of Na2CO3 = …… mol [1] (iii) Calculate the mass of anhydrous sodium carbonate present in the number of moles in your answer to (b)(ii). mass of Na2CO3 = …… g [1] (iv) Use your answer to (b)(iii) to calculate the percentage purity of anhydrous sodium carbonate in FB 3. percentage purity = …… [1] (c) In (b)(iv) you calculated the percentage purity of anhydrous sodium carbonate in FB 3. What did you assume about the impurity present? . …… . …… [1] (d) You carried out two experiments to measure the temperature change when anhydrous sodium carbonate was dissolved in water. Complete the sentence below to explain which of these experiments was more accurate. Your answer should not make reference to the fact that different masses of sodium carbonate were used. Experiment …… was more accurate because …… . …… . …… . [1] [Total: 11] Qualitative analysis Where reagents are selected for use in a test, the name or correct formula of the element or compound must be given. At each stage of any test you are to record details of the following: ● colour changes seen ● the formation of any precipitate and its solubility in an excess of the reagent added ● the formation of any gas and its identification by a suitable test. You should indicate clearly at what stage in a test a change occurs. If any solution is warmed, a boiling tube must be used. Rinse and reuse test-tubes and boiling tubes where possible. No additional tests for ions present should be attempted.

Mark scheme

2(a) I Table/lists given for at least one experiment 1 Unambiguous headings and correctly displayed units • (Mass of) cup • (Mass of) cup + FB 3 • (Mass of) FB 3 • Initial thermometer reading / temperature • Maximum / highest / final thermometer reading / temperature II Precision of all four readings 1 • thermometer readings to .5 °C • balance readings to same number of dp III Masses of FB 3 1.90 to 2.10 and 3.90 to 4.10 g 1 and subtractions correct IV and V Examiner to round thermometer readings to nearest .5 ºC, calculate ΔT values then calculate ratio to 1 dp: 2 ΔT experiment 2 / ΔT experiment 1 Award IV if 1.6 to 2.4 Award V if 1.8 to 2.2 2(b)(i) Correctly calculates heat energy = 25 × 4.2 × ΔT to 2–4 sf 1 2(b)(ii) (b)(i) 1 Correctly uses moles Na2CO3 = 28100 2(b)(iii) Correctly uses mass Na2CO3 = (b)(ii) × 106 1 Allow ecf for RFM anhydrous Na2CO3 in 1(c)(iv) 2(b)(iv) (b)(iii) 1 Correctly uses % = × 100 Mass FB3 from Expt 1 2(c) The enthalpy of solution of the impurity was = 0 / negligible / the impurity does not give out / absorb any heat / cause a 1 temperature change when it dissolves / impurity does not dissolve in water 2(d) Experiment 1 was more accurate because a smaller temperature rise meant that heat losses were less. 1 OR Experiment 2 was more accurate because has a larger temperature rise and therefore a smaller percentage error in temperature rise.

Question 315 marks

Question

(a) FB 4 and FB 5 each contain one cation and one anion from those listed in the Qualitative Analysis Notes. Carry out the following tests and record your observations. observations test FB 4 FB 5 Test 1 Heat a spatula measure of solid in a hard-glass test-tube gently at first and then more strongly, then leave the tube to cool. Test 2 To a small spatula measure of solid in a boiling tube add a 2 cm depth of dilute sulfuric acid. [5] (b) FB 6 is a solution prepared by reacting FB 4 with dilute sulfuric acid. FB 7 is a solution prepared by reacting FB 5 with dilute sulfuric acid. In each test use a 1 cm depth of FB 6 or FB 7 in a test-tube. Carry out the tests and record your observations. observations test FB 6 FB 7 Test 1 Add a 1 cm depth of aqueous edta. Test 2 Add aqueous sodium hydroxide until no further reaction occurs. Test 3 Add aqueous ammonia until no further reaction occurs. Test 4 Add a 1 cm length of magnesium ribbon and leave to stand for a few minutes. Test 5 Add a 2 cm depth of aqueous potassium iodide, then add a few drops of starch indicator. Test 6 Add concentrated hydrochloric acid (CARE) drop by drop until no further change is seen. Wash the test-tube thoroughly with plenty of water once your observations are complete. [7] (c) Complete the table with the formula of each cation and each anion in FB 4 and FB 5. If you are unable to identify an ion write ‘unknown’. FB 4 FB 5 cation anion [2] (d) Write the ionic equation for the reaction between FB 6 and magnesium. Include state symbols. . …… [1] [Total: 15] Qualitative analysis notes 1 Reactions of aqueous cations reaction with ion NaOH(aq) NH3(aq) aluminium, white ppt. white ppt. Al 3+(aq) soluble in excess insoluble in excess ammonium, no ppt. – NH4+(aq) ammonia produced on heating barium, faint white ppt. is nearly always no ppt. Ba2+(aq) observed unless reagents are pure calcium, white ppt. with high [Ca2+(aq)] no ppt. Ca2+(aq) chromium(III), grey-green ppt. grey-green ppt. Cr3+(aq) soluble in excess insoluble in excess copper(II), pale blue ppt. pale blue ppt. soluble in excess Cu2+(aq) insoluble in excess giving dark blue solution green ppt. turning brown on contact green ppt. turning brown on contact iron(II), with air with air Fe2+(aq) insoluble in excess insoluble in excess iron(III), red-brown ppt. red-brown ppt. Fe3+(aq) insoluble in excess insoluble in excess magnesium, white ppt. white ppt. Mg2+(aq) insoluble in excess insoluble in excess off-white ppt. rapidly turning brown off-white ppt. rapidly turning brown manganese(II), on contact with air on contact with air Mn2+(aq) insoluble in excess insoluble in excess zinc, white ppt. white ppt. Zn2+(aq) soluble in excess soluble in excess 2 Reactions of anions ion reaction carbonate, CO2 liberated by dilute acids CO32– chloride, gives white ppt. with Ag+(aq) (soluble in NH3(aq)) Cl –(aq) bromide, gives cream ppt. with Ag+(aq) (partially soluble in NH3(aq)) Br –(aq) iodide, gives yellow ppt. with Ag+(aq) (insoluble in NH3(aq)) I –(aq) nitrate, NH3 liberated on heating with OH–(aq) and Al foil NO3–(aq) nitrite, NH3 liberated on heating with OH–(aq) and Al foil NO2–(aq) sulfate, gives white ppt. with Ba2+(aq) (insoluble in excess dilute strong acids) SO4 (aq) 2– sulfite, gives white ppt. with Ba2+(aq) (soluble in excess dilute strong acids) SO3 (aq) 2– 3 Tests for gases gas test and test result ammonia, NH3 turns damp red litmus paper blue carbon dioxide, CO2 gives a white ppt. with limewater (ppt. dissolves with excess CO2) chlorine, Cl 2 bleaches damp litmus paper hydrogen, H2 ‘pops’ with a lighted splint oxygen, O2 relights a glowing splint The Periodic Table of Elements Group 1 2 13 14 15 16 17 18 1 2 H He hydrogen helium Key 1.0 4.0 3 4 atomic number 5 6 7 8 9 10 Li Be atomic symbol B C N O F Ne lithium beryllium name boron carbon nitrogen oxygen fluorine neon 6.9 9.0 relative atomic mass 10.8 12.0 14.0 16.0 19.0 20.2 11 12 13 14 15 16 17 18 Na Mg Al Si P S Cl Ar sodium magnesium aluminium silicon phosphorus sulfur chlorine argon 23.0 24.3 3 4 5 6 7 8 9 10 11 12 27.0 28.1 31.0 32.1 35.5 39.9 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 at www.cambridgeinternational.org after the live examination series. K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr potassium calcium scandium titanium vanadium chromium manganese iron cobalt nickel copper zinc gallium germanium arsenic selenium bromine krypton 39.1 40.1 45.0 47.9 50.9 52.0 54.9 55.8 58.9 58.7 63.5 65.4 69.7 72.6 74.9 79.0 79.9 83.8 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 12 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe rubidium strontium yttrium zirconium niobium molybdenum technetium ruthenium rhodium palladium silver cadmium indium tin antimony tellurium iodine xenon 85.5 87.6 88.9 91.2 92.9 95.9 – 101.1 102.9 106.4 107.9 112.4 114.8 118.7 121.8 127.6 126.9 131.3 55 56 57–71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 lanthanoids Cs Ba Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn caesium barium hafnium tantalum tungsten rhenium osmium iridium platinum gold mercury thallium lead bismuth polonium astatine radon 132.9 137.3 178.5 180.9 183.8 186.2 190.2 192.2 195.1 197.0 200.6 204.4 207.2 209.0 – – – 87 88 89–103 104 105 106 107 108 109 110 111 112 114 116 actinoids Fr Ra Rf Db Sg Bh Hs Mt Ds Rg Cn Fl Lv francium radium rutherfordium dubnium seaborgium bohrium hassium meitnerium darmstadtium roentgenium copernicium flerovium livermorium – – – – – – – – – – – – – 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 lanthanoids La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu lanthanum cerium praseodymium neodymium promethium samarium europium gadolinium terbium dysprosium holmium erbium thulium ytterbium lutetium 138.9 140.1 140.9 144.4 – 150.4 152.0 157.3 158.9 162.5 164.9 167.3 168.9 173.1 175.0 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 actinoids Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr actinium thorium protactinium uranium neptunium plutonium americium curium berkelium californium einsteinium fermium mendelevium nobelium lawrencium – 232.0 231.0 238.0 – – – – – – – – – – – Assessment International Education Copyright Acknowledgements Booklet. This is produced for each series of examinations and is freely available to download To avoid the issue of disclosure of answer-related information to candidates, all copyright acknowledgements are reproduced online in the Cambridge

Mark scheme

3(a) 5 FB 4 FB 5 Test 1 blue / green solid * white solid * heat goes black * goes yellow * condensation in either * cooling ignore white / paler solid * Test 2 bubbles in both * + H2SO4 blue soln * colourless soln * attempts limewater in either * white ppt / turns milky / cloudy white * 2 * = 1 mark (round down) 3(b) test FB 6 FB 7 7 edta turns brighter / more intense / darker blue * No (visible) change / no reaction * ALLOW light blue to dark blue ALLOW (solution) stays colourless NaOH Blue ppt White ppt * and insoluble in excess * Soluble in excess * NH3 (Pale) blue ppt * White ppt * (Soluble excess to) dark blue solution * Soluble in excess * Mg Pink / brown / dark grey / black solid * ALLOW ppt Blue fades / bubbles * KI Brown / yellow-brown / ochre * (ignore state) + starch Black / blue-black / dark blue * HCl (Solution) goes green / yellow * 2 asterisks = 1 mark (round down) 3(c) 2 asterisks = 1 mark (round down) 2 FB 4 FB 5 cation Cu2+* Zn2+* anion CO32–* CO32–* 3(d) Cu2+(aq) + Mg(s) → Cu(s) + Mg2+(aq) 1 If bubbles recorded in test 4, allow Mg(s) + 2H+(aq) → Mg2+(aq) + H2(g) Allow ecf on identity of FB 6

Checked your answers against these? Let AI mark the whole paper, on your own working.

Mark my 9701/32

How this paper is marked

Examiners follow the generic marking principles at the front of the scheme, then each question's points: method (M), accuracy (A) and independent (B) marks, error carried forward where the scheme allows it, and positive marking, so you're credited for what you got right.

Check your answers against it

Done this paper? Upload your script and CIE Buddy's AI marker marks it question by question against this exact scheme, puts the ticks on your own working and says what each lost mark needed.

Other variants, May/June 2021

9701/32 in other series

Find another Chemistry paper

Every AS & A Level Chemistry mark scheme

Question papers and mark schemes © Cambridge University Press & Assessment. CIE Buddy is independent and not connected to Cambridge.

9701/32 questions

Where can I find the 9701/32 May/June 2021 mark scheme?

On this page, free: the mark scheme for AS & A Level Chemistry 9701/32, May/June 2021 (9701_s21_ms_32), and the question paper (9701_s21_qp_32), to read or download, with each question's marking points written out underneath.

How many marks is 9701/32 out of?

Chemistry 9701/32 for May/June 2021 is out of 40 marks, across 3 questions.

Can I get my 9701/32 answers marked?

Yes. Upload your answers to 9701/32/M/J/21 as a PDF or photos, and CIE Buddy marks every question against this paper's official mark scheme, using Cambridge's marking rules. You get your score, each lost mark explained on your own script, and the topics to revise. It's a guide, not an official Cambridge grade.