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

Get started

Chemistry 9701/35 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_359701_s21_ms_359701/35/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
9701/35/M/J/21
9701_s21_ms_35.pdf

9701/35 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 118 marks

Question

In this experiment you will carry out a titration to determine the relative formula mass, Mr, of a monoprotic acid, HX. FA 1 is HX, the monoprotic acid. FA 2 is 0.0450 mol dm–3 sodium carbonate, Na2CO3. methyl orange indicator (a) Method Preparing a solution of FA 1 ● Weigh the empty 250 cm3 beaker. Record the mass. ● Transfer all the FA 1 into the beaker. ● Weigh the beaker and FA 1. Record the mass. ● Calculate and record the mass of FA 1 used. ● Add approximately 100 cm3 of distilled water to the FA 1 in the beaker. ● Stir the mixture with a glass rod until all the FA 1 has dissolved. ● Transfer this solution into the 250 cm3 volumetric flask. ● Wash the beaker with distilled water and transfer the washings to the volumetric flask. ● Rinse the glass rod with distilled water and transfer the washings to the volumetric flask. ● Make up the solution in the volumetric flask to the mark using distilled water. ● Shake the flask thoroughly. ● This solution of HX is FA 3. Label the flask FA 3. Results Titration ● Fill the burette with FA 3. ● Pipette 25.0 cm3 of FA 2 into a conical flask. ● Add several drops of methyl orange indicator. ● Perform 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 any recorded results show the precision of your practical work. ● Record in a suitable form below all of your burette readings and the volume of FA 3 added in each accurate titration. I II III IV V VI VII VIII [8] (b) From your accurate titration results, obtain a suitable value for the volume of FA 3 to be used in your calculations. Show clearly how you obtained this value. 25.0 cm3 of FA 2 required …… cm3 of FA 3. [1] (c) Calculations (i) Calculate the number of moles of sodium carbonate present in the volume of FA 2 used in each titration. moles of Na2CO3 = …… mol [1] (ii) Give the equation for the reaction of FA 2, Na2CO3, with FA 3, HX. ……Na2CO3 + ……HX → ……NaX + …… + …… Use your answer to (c)(i) to deduce the number of moles of HX present in the volume you calculated in (b). moles of HX = …… mol [1] (iii) Use your answer to (c)(ii) and your data recorded on page 2 to calculate the relative formula mass, Mr, of HX. Show your working. Mr of HX = …… [2] (iv) One molecule of HX contains one nitrogen atom, three oxygen atoms, three hydrogen atoms and one atom of another element, E. The identity of E can be found by calculation. Show this calculation and identify E. Element E is …… . [1] (d) What is the error in a single reading for the balance that you used? error = …… g Calculate the maximum percentage error in the mass of FA 1 that you recorded on page 2. maximum percentage error = …… % [1] (e) Suggest and carry out an experiment using aqueous silver nitrate to determine whether the compound AgX is soluble or insoluble in water. method . …… . …… observations …… conclusion . …… [2] (f) Suggest why the use of methyl orange indicator might give an inaccurate titration result. . …… . …… [1] [Total: 18]

Mark scheme

1(a) l Unambiguous headings and data are recorded in the space provided 1 • mass of container with FA 1 (do not allow ‘weight’) • mass of (empty) container • mass of FA 1 used II All the following data is recorded 1 • two burette readings and titre for the rough titration • initial and final burette readings for two (or more) accurate titrations III Titre values recorded for accurate titrations, and 1 appropriate headings and units in the accurate titration table • initial / start and (burette) reading / volume • final / end and (burette) reading / volume • titre or volume used / added / or FA 3 added (not ‘difference’ or ‘total’ or ‘amount’) Allow ‘Vol’, but not V • unit: /cm3 or (cm3) or in cm3 (for each heading) or cm3 unit given for each volume recordedUnits: (cm3) or /cm3 or in cm3 or cm3 by every entry 1(a) IV All accurate burette readings to 0.05 cm3 1 V The final accurate titre recorded is within 0.10 cm3 of any other accurate titre 1 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 products of mass and titre for candidate and supervisor to one d.p, as shown below. • Product = ‘best’ mean titre × mass of FA 1 used. (Theoretical product value = 56.0 cm3 g) If no weighings are discernible, assume mass of FA 1 = 2.25 g Calculate the difference (δ) between the candidate’s product and the supervisor’s product. Award the accuracy (Q) marks as shown below. Award accuracy marks as follows: 8 VI Award if δ ⩽ 2.0 cm3 g VII Award if δ ⩽ 1.0 cm3 g VIII Award if δ ⩽ 0.5 cm3 g (3) 1(b) Correctly calculates mean accurate titre 1 • Candidate must take the average of two (or more) titres that are within a total spread of not more than 0.20 cm3. • Working/explanation must be shown or ticks must be put next to the two (or more) accurate readings selected. • The mean should be quoted to 2 dp and be rounded to nearest 0.01 cm3. 1(c)(i) Correctly calculates (to 3 or 4 sig fig) 1 No of moles of Na2CO3 used = 0.00113 or 0.001125 1(c)(ii) Correct equation AND calculates moles of HX 1 • Na2CO3 + 2HX → 2NaX + CO2 + H2O and • No of moles of HX = 0.00226(0) or 0.00225(0) 1(c)(iii) Correct expression shown for scale up 2 M1: No of moles HX in 250 cm3 = (c)(ii) × 250 / mean titre Correctly uses expression for Mr M2: Mr = mass of FA 1 used/moles of FA 1 in 250 cm3 and answer given to 3 or 4 sf and to the correct power of 10 1(c)(iv) Appropriate identity of E 1 Ar = answer (iii) − 14 − 3 − 48 (= (iii) – 65) and E chosen with Ar closest to this value. 1(d) Correct expression for % error 1 = (2 × balance error/mass of FA1 used) x 100 1(e) M1: Method 2 Add (aqueous silver nitrate to) FA 3 or to a solution of FA 1 M2: Observation and conclusion No reaction / no change / no precipitate / colourless solution (formed) and AgX is soluble 1(f) Accept one answer from 1 • end-point colour change is indistinct / difficult to see • colour change occurs over addition of significant volume • accept an answer based on pH curve – e.g. colour change range not within ‘vertical’ part of graph

Question 27 marks

Question

You will determine the percentage by mass of water of crystallisation in a hydrated salt by thermal decomposition. When a hydrated salt is heated it loses its water of crystallisation. FA 4 is the hydrated salt. (a) Method ● Weigh the crucible with its lid. Record the mass. ● Transfer 2.0–2.2 g of FA 4 from the container into the crucible. ● Weigh the crucible, lid and FA 4. Record the mass. ● Calculate and record the mass of FA 4 used. ● Place the crucible and contents on the pipe-clay triangle. ● Heat gently, with the lid on, for approximately 1 minute. ● Heat strongly, with the lid off, for a further 4 minutes. ● Replace the lid and leave the crucible to cool for at least 5 minutes. During the cooling period, you may wish to begin work on Question 3. ● When the crucible is cool, weigh the crucible with its lid and contents. Record the mass. ● Heat strongly, with the lid off, for a further 2 minutes. ● Replace the lid and leave the crucible to cool for at least 5 minutes. ● When it is cool, weigh the crucible with its lid and contents. Record the mass. ● Calculate and record the mass lost. Keep FA 4 for use in Question 3. Results I II III IV V [5] (b) (i) Calculate the percentage by mass of water of crystallisation in FA 4. percentage by mass of H2O in FA 4 = …… % [1] (ii) State what assumption you made about anhydrous FA 4 in your calculation in (b)(i). . …… . …… [1] [Total: 7] 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 Unambiguous headings and correct units for four weighings 1 • Mass of crucible, lid (empty) • Mass of crucible, lid and FA 4 (or ‘contents before heating’) • Mass of crucible, lid and contents after heating / residue (1) • Mass of crucible, lid and contents after heating / residue (2) II Readings are appropriately recorded 1 • All weighings shown are recorded to same decimal places (one or more). • Mass of FA 4 is within range 2.00–2.20 g (from weighings) Third and fourth weighings are within 0.04 g of each other (or identical if a 1 dp balance was used) III Correct subtractions (answers given to 2 or more sig fig) 1 and Mass of FA 4 used and mass of water lost both listed. Accuracy marks Use the theoretical mass ratio water/FA 4 = 0.147 • Examiner must check and correct (if needed) the mass of FA 4 used and water removed (after re-heating) by the candidate. • Work out ratio mass of water/mass of FA 4 for the candidate (to 3 dp) Award accuracy marks as follows: IV Award if ratio in range 0.137–0.157 5 V Award if ratio in range 0.142–0.152 (2) 2(b)(i) Correctly calculates percentage by mass of water 1 Answer = ratio (see above) × 100 2(b)(ii) Assumption 1 The residue does not decompose when heated / the mass loss is only due to water (OWTTE) FA 4 is BaCl 2•2H2O; FA 5 is (NH4)2CO3

Question 315 marks

Question

(a) FA 4 contains one cation and one anion both of which are listed in the Qualitative Analysis Notes. Dissolve the remainder of the FA 4 in approximately 20 cm3 of water in the 100 cm3 beaker. Use a 1 cm depth of this solution in a test-tube for each of the tests. (i) The anion in FA 4 is chloride. State which reagents you would use to identify this ion conclusively. . …… Use your reagents to test your solution of FA 4. Record your observations. . …… . …… . …… In what way are your observations not consistent with the expected results for chloride? . …… . …… [3] (ii) Add an equal volume of dilute sulfuric acid to aqueous FA 4. Record your observations and deduce the identity of the cation in FA 4. observations …… identity of cation . …… Give the ionic equation for this reaction. Include state symbols. . …… [2] (b) Use the conclusions in (a)(i) and (a)(ii) to calculate the relative formula mass of anhydrous FA 4. Mr = …… Use your results from Question 2 to calculate the number of moles of water of crystallisation in one mole of hydrated FA 4. moles of H2O = …… [3] (c) FA 5 contains one cation and one anion, both of which are listed in the Qualitative Analysis Notes. (i) Heat a small spatula measure of FA 5 in a hard-glass test-tube. Keep heating until no further change is observed. Record all your observations. . …… . …… . …… . …… [2] (ii) To a 1 cm depth of dilute sulfuric acid in a test-tube, add a small spatula measure of FA 5. Record all your observations. . …… . …… . …… . …… . …… [3] (iii) Place a small spatula measure of FA 5 into a boiling tube. Add a 1 cm depth of aqueous sodium hydroxide and warm the mixture gently. Record your observations. . …… . …… [1] (iv) From the results of your tests, deduce the chemical formula of FA 5. FA 5 is …… . [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 CO3 2– 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) SO42–(aq) 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)(i) Correct reagents 3 M1: (Reagents needed are) silver nitrate and ammonia M2: White ppt with AgNO3 and Precipitate is partially / mostly soluble in (excess) ammonia. M3: the precipitate (of silver chloride) should dissolve completely in excess ammonia/ the ppt is insoluble in (excess) ammonia 3(a)(ii) M1: White precipitate / solid 2 and cation is barium M2: Ionic equation Ba2+(aq) + SO42–(aq) → BaSO4(s) 3(b) Calculation of no of moles of water 3 M1: Mr of anhydrous salt = 208.3 M2: n(anhy salt : water) =mass residue : mass water Mr 18 = ans : ans M3: ratio of moles and answer given to integer value or up to 4 sf OR M2: Candidate shows valid working to calculate Mr of hydrated salt or working to calculate mass of water from 1 mole FA 4. (e.g. Mr (hydrated salt) = 208.3 × mass FA 4 used / mass residue) or mass water (in 1 mol FA 4) = 208.3 × mass water lost / mass of residue M3 Candidate attempts to divide mass of water by 18 and expresses moles of water as an integer or up to 4 sf 3(c)(i) Heating FA 5: there are four marking points 2 * FA 5 is a white solid / powder / crystals * Condensation / steam / water vapour forms * (Gas / vapour / ammonia) turns (red) litmus blue * No residue / solid left (in the tube) or solid disappears / sublimes 3 or 4 asterisks (*) = 2 marks 2 asterisks (*) = 1 mark 3(c)(ii) FA 5 + acid: there are 6 marking points 3 *Fizzing / bubbling / effervescence (but not ‘gas produced’) *Rapid / vigorous (reaction) owtte *Solid dissolves / (colourless) solution formed *Reaction is endothermic / solution gets colder *Attempts to test with limewater *Gas / carbon dioxide turns limewater milky / white precipitate ‘cloudy’ is not accepted, but ‘cloudy white’ is OK. 2 asterisks (*) = 1 mark (round down) 3(c)(iii) gas / ammonia turns (red) litmus blue. 1 3(c)(iv) Conclusion 1 FA 5 is (NH4)2CO3

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

Mark my 9701/35

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

9701/35 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.

9701/35 questions

Where can I find the 9701/35 May/June 2021 mark scheme?

On this page, free: the mark scheme for AS & A Level Chemistry 9701/35, May/June 2021 (9701_s21_ms_35), and the question paper (9701_s21_qp_35), to read or download, with each question's marking points written out underneath.

How many marks is 9701/35 out of?

Chemistry 9701/35 for May/June 2021 is out of 40 marks, across 3 questions.

Can I get my 9701/35 answers marked?

Yes. Upload your answers to 9701/35/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.