Chemistry 9701/34 May/June 2020: question paper and mark scheme
Cambridge AS & A Level Chemistry (9701), Paper 3 Paper 34 (Advanced Practical Skills 2), May/June 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 Initial and final burette readings and volume added recorded for rough titre and accurate titre details tabulated. 1
II Initial and final burette readings recorded and vol of 1
FB 3 added recorded for each accurate titration.
Headings and units correct for accurate titrations.
Headings: initial / final (burette) reading / volume or reading / volume at start / finish
and
volume / FB 3 added/used or titre
and
units (cm3) or / cm3 or in cm3 or cm3 by every entry
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 0.10 cm3 of any other accurate titre. 1
1(a) V, VI and VII 3
Award V, VI and VII for δ ⩽ 0.30 cm3
Award V and VI for 0.30 cm3 < δ ⩽ 0.50 cm3
Award V for 0.30 cm3 < δ ⩽ 0.80 cm3
1(b) Calculation of mean 1
Candidate must average two (or more) accurate titres where the total spread is ⩽ 0.20 cm3.
Working must be shown or ticks must be put next to the two (or more) accurate readings selected.
1(c)(i) all answers to (ii), (iii), (iv) and (v) to 3–4 sf (minimum 4 answers) 1
1(c)(ii) (b) × 0.100 1
Correctly calculates moles NaOH = to 3–4 sf
1000
and
same answer for moles of HCl
1(c)(iii) 25.0 × 0.200 1
Correctly calculates moles HCl = = 5.00 × 10−3
1000
and
moles neutralised = moles HCl above – moles HCl in (i)
1(c)(iv) Na2CO3(aq) + 2HCl (aq) → 2NaCl(aq) + CO2(g) + H2O(l) 1
and
moles in HCl in (ii)
correctly uses moles Na2CO3 =
2
1(c)(v) ans (iii) × 100 1
37.5 / ((iii) × 100)
can be done in either order
37.5
moles = = 2 marks
100 × (iii)
any error loses 1 mark
1(c)(vi) Correctly calculates x ((Mr –106) / 18) and gives to nearest integer 1
allow ecf even if negative integer.
1(d) Disadvantage: if make mistake all the solution is wrong 1
Advantage: quicker/ larger volume has less % error
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 Table with headings and units for 3 weighings and 3 calculated masses 1
II Mass FB 4 used between 1.80 and 2.20 g 1
masses of FB 4, residue and water lost correctly calculated.
III Ratio within 1.95–2.15 of supervisor ratio 1
III and IV Ratio within 2.00–2.10 of supervisor ratio 1
2(b)(i) mass water 1
Correctly calculates moles water = to 2–4sf
18
Penalise sf only once in this question.
2(b)(ii) MSO4.7H2O(s) → MSO4(s) + 7H2O(g) 1
and
correctly uses moles anhydrous = (ii) / 7
2(b)(iii) FB 4 1
Correctly uses mass = Mr
moles anhydrous
2(b)(iv) Shows Ar M + 222.1 = Mr FB 4 1
and
calculates Ar of M
identifies M as Group 2 metal with nearest Ar 1
2(c)(i) To avoid water being picked up (from air) 1
2(c)(ii) Ar higher with explanation 1
Mass water lost less → moles water lost less → moles anhydrous more → Mr higher → Ar higher
very little effect because very little water vapour absorbed
if lid prevented loss in (i) then allow Ar lower as ecf
FB 5 is Zn FB 6 is ZnSO4.7H2O FB 7 is propanone
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) (Yellow solution goes) to blue / green 1
then to lilac / violet / mauve 1
3(a)(ii) any two from; 1
• blue (ignore green if before blue)
• green / yellow
• KMnO4 loses purple colour
3(a)(iii) Redox 1
3(a)(iv) Fizz / bubbles / effervescence 1
Gas / H2 (gas) burns with a pop / pops with a lighted splint 1
3(b)(i) 2
test observation
FB 6 + NaOH white ppt* soluble in excess*
FB 6 + NH3 white ppt* soluble in excess *
Award one mark for every two correct observations (*)
3(b)(ii) FB 5 is Zn / zinc (metal) 1
3(b)(iii) Zn(s) + H2SO4(aq) → ZnSO4(aq) + H2(g) 1
ecf for incorrect FB 5 provided gas is produced.
3(c)(i) Choice of reagent: Tollens’ and warming / Fehling’s and warming / Benedict’s and warming / Sandell’s and warming / 1
acidified potassium manganate(VII)
Positive test for ethanal – silver mirror / black (or dark grey) solid for Tollens’ 1
Red / brown (solid / ppt) for Fehling’s / Benedict’s / Sandell’s
Purple to colourless for acidified manganate(VII)
negative result for propanone – no reaction
3(c)(ii) Negative test result and 1
FB 7 is propanone
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Chemistry 9701/34 for May/June 2020 is out of 40 marks, across 3 questions.
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