Chemistry 9701/36 October/November 2020: question paper and mark scheme
Cambridge AS & A Level Chemistry (9701), Paper 3 Advanced Practical Skills 2, October/November 2020. Read both free below, or download them. Done the paper? Get it marked by AI against this mark scheme.
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. 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
Mark scheme
1(a) I Unambiguous headings in layout of weighings 1
and
correct mass of FB 1 added
and
units correct: / g, (g) or in gram(me)s
Reject ‘weight’
II Unambiguous recording of volume of CO2 with correct unit 1
III Volume of gas collected is in the range 120−240 cm3 1
Allow gas volume from (b)(i) if not recorded in (a)
Note: if more than one expt. has been performed then all volumes collected must be within the limits above
1(b)(i) Correctly calculates 1
V (a)
24.0 × 1000
and
answer given to 2‒4 sf
1(b)(ii) Correctly uses 1
mass FB 1 from (a)
(b)(i)
and
answer given to 2‒4 sf
1(b)(iii) Correct expression 1
(b)(ii) −138.2
18
Note: 138.2 or 39.1 must be seen
Allow expression to be shown in two (or more) steps
x given as correct integer from candidate’s expression 1
1(c) Any 2 of the following: 2
• Heat water (before collecting gas)
• Saturate water with CO2 (before collecting gas)
• Collect the gas over a (dilute) strong acid / any non-alkaline solution / use more concentrated acid in flask
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–
Mark scheme
2(a) I Headings and units 1
Data set out in horizontal / vertical lines / columns showing
• 2 × mass of container + solid / FB 3 / FB 4
• 2 × mass of container (+ residue)
• 2 × initial thermometer reading / temperature
• 2 × highest / lowest / final thermometer reading / temperature
• 2 × mass of solid (used / added) / FB 3 / FB 4
• 2 × ∆T / change in temperature
Units: / g, (ºC), in gram(me)s
Reject ‘weight’ unless already penalised in 1(a)
Note: data must be included but not necessarily correct.
II All four balance readings recorded to the same number of dp and thermometer readings recorded to .0 °C or .5 °C 1
and written in the table
Reject if all temperatures are below 10.0 °C
III Correctly calculates 1
2 × mass of solid
2 × change in temperature (ignore sign)
Allow from 2(b)(i) and 2(b)(ii) if correctly calculated
Examiner checks subtractions of supervisor and candidate.
Write supervisor values (ringed) on the candidate script and calculate the differences, δ, from candidate.
2(a) Award IV, V (Expt 1) and VI, VII (Expt 2) according to the table. 4
Supervisor ΔT 5.0–10.0 °C < 5.0 °C
1 mark δ = 1.5 °C δ = 1.0 °C
2 marks δ = 1.0 °C δ = 0.0 °C
2(b)(i) Correctly calculates 1
Q (heat energy) = 25 × 4.2 × ΔT for both experiments and answers to 2–4 sf
Allow ecf from incorrect ΔT
Ignore signs
Do not penalise incorrect sf more than once in (b)
2(b)(ii) Correctly uses 2
( 25 × 4.2 × ΔT ) × 106 ( 25 × 4.2 × ΔT ) × 286
mass FA 3 × 1000 mass FA 4 × 1000
One mark awarded for each correct calculation.
Correct signs shown and answers given to 2–4 sf 1
2(b)(iii) Attempt at use of Hess’ law / energy level diagram / reverse equation 1
Note: minimum display of working is correct direction of arrows and correct numbers shown / equations labelled and correct
numbers shown)
Correctly uses 1
ΔH1 ─ ΔH2 and correct sign and answer to 2–4 sf
(Default answer = ‒ 72.9)
2(c) No effect and same number / moles / amount / concentration of hydrogen ions 1
FB 6 is Na2CO3(aq); FB 7 is CrCl3(aq); FB 8 is FeSO4(aq)
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) 14 observations. Two * = 1 mark (round down) 7
FB 6 FB 7 FB 8
+ NH3 no (visible) reaction / no change / grey-green ppt and insoluble in green ppt and insoluble in
no ppt * excess * excess / turns brown *
+ H2SO4 effervescence / bubbling / fizzing * no (visible) reaction / no change * no (visible) reaction / no change *
ignore no ppt ignore no ppt
limewater test attempted *
gas / CO2 turns limewater milky /
cloudy white / forms white ppt *
+ H+ / MnO4‒ purple remains / purple remains / no reaction / no purple / MnO4− and
no reaction / no change / purple change / purple not decolourised / solution turns
not decolourised * decolourised / turns darker yellow *
purple *
fizzing *
(limewater test and observation
may be awarded here)
+ FB 6 green ppt * (pale) green ppt *
ignore excess ignore excess
allow white- green / grey-green ignore turning brown
ppt
(limewater test and observation
can be awarded here)
3(a)(ii) Carbonate or hydrogen carbonate identified from correct formula 1
2H+(aq) + CO32‒(aq) → H2O(l) + CO2(g) 1
Allow H+(aq) + HCO3‒(aq) → H2O(l) + CO2(g)
3(a)(iii) All three correct = 2 marks, 2 correct = 1 mark 2
FB 6 = unknown (Ignore Na+)
FB 7 = Cr3+
FB 8 = Fe2+
Allow unknown and chromium(III) and iron(II) for 1 mark
3(b)(i) Uses AgNO3(aq) for halides and Ba(NO3)2(aq) / BaCl2(aq) for S-anion 1
OR
AgNO3 then NH3 for halide (any named halide)
OR
Ba(NO3)2(aq) / BaCl2 followed by HCl / HNO3 for S-anion (sulfate and sulfite)
Allow Ba(NO3)2(aq) / BaCl2 then (separate test) (acidified) KMnO4 for S-anion (sulfate and sulfite)
Allow without state symbols.
Ignore separate test of adding acid (test for carbonate).
Ignore addition of HNO3 before adding AgNO3.
3(b)(ii) Clear presentation in a ‘table’ of results to show FB 7 and FB 8 and two or more reagents. 1
Note: the reagents need not be correct for this mark to be awarded
Note: no observations are needed for this mark to be awarded
6 observations. 2 * = 1 mark (round down) 3
test observation
FB 7 FB 8
+ Ag+ white ppt • (slowly forms) (pale) brown ppt •
allow no change
+ NH3 ppt turns grey-green / green ppt * ignore
Reject ppt dissolves
+ Ba2+ no reaction / no change • white ppt •
+ H+ to ppt OR ignore ppt insoluble •
(allow) + KMnO4 to soln. ignore purple to colourless / yellow – as (a)(i) *
Ignore observations for any other reagents
3(b)(iii) Both ions correct = 1 mark 1
FB 7 = Cl ‒
FB 8 = SO42‒
Ignore names of ions
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On this page, free: the mark scheme for AS & A Level Chemistry 9701/36, October/November 2020 (9701_w20_ms_36), and the question paper (9701_w20_qp_36), to read or download, with each question's marking points written out underneath.
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Chemistry 9701/36 for October/November 2020 is out of 40 marks, across 3 questions.
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