Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level. Published

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1 Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level CHEMISTRY 970/ Paper Multiple Choice May/June 207 MARK SCHEME Maximum Mark: 40 Published This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of the examination. Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for Teachers. Cambridge will not enter into discussions about these mark schemes. Cambridge is publishing the mark schemes for the May/June 207 series for most Cambridge IGCSE, Cambridge International A and AS Level and Cambridge Pre-U components, and some Cambridge O Level components. IGCSE is a registered trademark. This document consists of 3 printed pages. UCLES 207 [Turn over

2 970/ Cambridge International AS/A Level Mark Scheme May/June 207 C 2 D 3 A 4 C 5 B 6 A 7 D 8 C 9 B 0 C B 2 A 3 B 4 A 5 C 6 C 7 A 8 C 9 A 20 B 2 D 22 B 23 B 24 C 25 D 26 C 27 A 28 C UCLES 207 Page 2 of 3

3 970/ Cambridge International AS/A Level Mark Scheme May/June A 30 B 3 B 32 D 33 D 34 A 35 D 36 A 37 B 38 D 39 B 40 A UCLES 207 Page 3 of 3

4 Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level CHEMISTRY 970/2 Paper Multiple Choice May/June 207 MARK SCHEME Maximum Mark: 40 Published This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of the examination. Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for Teachers. Cambridge will not enter into discussions about these mark schemes. Cambridge is publishing the mark schemes for the May/June 207 series for most Cambridge IGCSE, Cambridge International A and AS Level and Cambridge Pre-U components, and some Cambridge O Level components. IGCSE is a registered trademark. This document consists of 3 printed pages. UCLES 207 [Turn over

5 970/2 Cambridge International AS/A Level Mark Scheme May/June 207 B 2 B 3 C 4 D 5 A 6 D 7 C 8 C 9 A 0 A C 2 B 3 B 4 C 5 D 6 C 7 D 8 D 9 B 20 D 2 D 22 C 23 A 24 D 25 D 26 B 27 D 28 A UCLES 207 Page 2 of 3

6 970/2 Cambridge International AS/A Level Mark Scheme May/June D 30 C 3 B 32 C 33 C 34 A 35 B 36 A 37 B 38 B 39 A 40 B UCLES 207 Page 3 of 3

7 Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level CHEMISTRY 970/3 Paper Multiple Choice May/June 207 MARK SCHEME Maximum Mark: 40 Published This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of the examination. Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for Teachers. Cambridge will not enter into discussions about these mark schemes. Cambridge is publishing the mark schemes for the May/June 207 series for most Cambridge IGCSE, Cambridge International A and AS Level and Cambridge Pre-U components, and some Cambridge O Level components. IGCSE is a registered trademark. This document consists of 3 printed pages. UCLES 207 [Turn over

8 970/3 Cambridge International AS/A Level Mark Scheme May/June 207 A 2 D 3 B 4 B 5 D 6 B 7 A 8 B 9 A 0 B B 2 C 3 C 4 B 5 D 6 A 7 D 8 B 9 C 20 C 2 C 22 D 23 A 24 C 25 D 26 D 27 B 28 A UCLES 207 Page 2 of 3

9 970/3 Cambridge International AS/A Level Mark Scheme May/June A 30 C 3 C 32 B 33 A 34 B 35 A 36 A 37 A 38 D 39 C 40 B UCLES 207 Page 3 of 3

10 Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level CHEMISTRY 970/2 Paper 2 AS Level Structured Questions May/June 207 MARK SCHEME Maximum Mark: 60 Published This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of the examination. It shows the basis on which Examiners were instructed to award marks. It does not indicate the details of the discussions that took place at an Examiners meeting before marking began, which would have considered the acceptability of alternative answers. Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for Teachers. Cambridge will not enter into discussions about these mark schemes. Cambridge is publishing the mark schemes for the May/June 207 series for most Cambridge IGCSE, Cambridge International A and AS Level and Cambridge Pre-U components, and some Cambridge O Level components. IGCSE is a registered trademark. This document consists of 7 printed pages. UCLES 207 [Turn over

11 970/2 Cambridge International AS/A Level Mark Scheme May/June 207 (a) The mass of a molecule OR the (weighted) average / (weighted) mean mass of the molecules Relative / compared to (the mass) of an atom of carbon 2 2 OR on a scale in which a carbon 2 atom / isotope has a mass of (exactly) 2 (units) (b)(i) 3 (b)(ii) 8 (b)(iii) C 3 H 8 O + 4½O 2 3CO 2 + 4H 2 O (b)(iv) AND propan 2 ol / 2 propanol AND propan ol / propanol Alternative answers (any two): AND butan ol / butanol AND butan 2 ol / 2 butanol AND (2 )methylpropan ol / (2 )methyl propanol AND (2 )methylpropan 2 ol / (2 )methyl 2 propanol UCLES 207 Page 2 of 7

12 970/2 Cambridge International AS/A Level Mark Scheme May/June 207 (b)(v) correct conversions of data to SI/consistent units p = ; V = ; T = 393 calculation of n ( = pvirt) from M values n = calculation of mass m ( = n Mr) AND answer correct to 3sf m = = (g) Alternative answer for using C 4 H 0 O: m = = (g) Total: 0 2(a) substance type of bonding type of lattice structure copper metallic giant/metallic ice covalent OR hydrogen(-bonding) / H( bonding) hydrogen-bonded / simple / molecular silicon(iv) oxide covalent giant (molecular) / macromolecular iodine covalent simple / molecular sodium chloride ionic giant / ionic 2(b)(i) hydrogen bonding UCLES 207 Page 3 of 7

13 970/2 Cambridge International AS/A Level Mark Scheme May/June 207 2(b)(ii) H-bond between O and H of different molecules minimum three partial charges (in a row) over two H 2 O molecules, i.e.: either δ O H δ δ O or H δ δ O H δ+ lone pair of electrons on O of H-bond, in line with H-bond 2(c)(i) X = liquid AND Z = solid Y = liquid and solid OR liquid / solid OR liquid OR solid 2(c)(ii) (kinetic) energy reducing motion slowing owtte 2(c)(iii) energy given out / released forming bonds / forming bonds exothermic compensates for / counteracts heat loss / cooling owtte Total: 5 UCLES 207 Page 4 of 7

14 970/2 Cambridge International AS/A Level Mark Scheme May/June 207 3(a)(i) A 3(a)(ii) H 3(a)(iii) G 3(a)(iv) B 3(a)(v) F 3(b)(i) (strong) heating (to provide / overcome) high activation energy 3(b)(ii) white flame / white light / white smoke / white solid 3(b)(iii) Mg(s) + 2H2O(l) Mg(OH) 2(s) + H 2(g) 2 3(c)(i) 2Mg(NO 3 ) 2 2MgO + 4NO 2 + O 2 3(c)(ii) CaCO 3 CaO + CO 2 CaO + H2O Ca(OH) 2 3(d)(i) reduce acidity in soil / increase ph of soil (both) basic / base(s) 3(d)(ii) + 2+ CaCO 3 + 2H Ca + CO 2 + H2O OR + 2+ CaCO + 2H Ca +H CO Total: 6 UCLES 207 Page 5 of 7

15 970/2 Cambridge International AS/A Level Mark Scheme May/June 207 Question 4(a)(i) Answerr (molecules / isomers with) the same molecular formula / same number of atoms of each element different structural / displayed formulae / arrangement of bonds Marks 4(a)(ii) sp 2 overlap of (2)s with two (2)p (atomic) orbitals sp 3 overlap of (2)s with all three (2)p (atomic) orbitals 4(a)(iii) 4(b)(i) sp 2 = 6 24 sp 3 = (b)(ii) 4(b)(iii) (electrophilic) addition bromine decolourises / turns colourless / fades (from orange / brown) HOCH 2 CHBrCH 2 Br OR 4(b)(iv) 4(c)(i) CO 2 / carbon dioxide P = propanal Q = propanone UCLES 207 Page 6 of 7

16 970/2 Cambridge International AS/A Level Mark Scheme May/June 207 Question 4(c)(ii) Answerr Marks tr(i)iodomethane / CHI 3 / / 4(d)(i) 4(d)(ii) (molecules / isomers with) the same (molecular and) structural formula Any two of: chiral centre / C attached to four different groups / atoms a non-super(im)posable mirror images different spatial / 3D arrangement of atoms (owtte) different rotation of plane-polarised light curly arrow from lone pair on :C N to C (δ+) correct dipole on carbonyl δ+ C=O δ AND curly arrow from bond b to O (δ ) correct intermediate, including C O AND curly arrow from lone pair to H + Total: 9 UCLES 207 Page 7 of 7

17 Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level CHEMISTRY 970/22 Paper 2 AS Level Structured Questions May/June 207 MARK SCHEME Maximum Mark: 60 Published This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of the examination. It shows the basis on which Examiners were instructed to award marks. It does not indicate the details of the discussions that took place at an Examiners meeting before marking began, which would have considered the acceptability of alternative answers. Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for Teachers. Cambridge will not enter into discussions about these mark schemes. Cambridge is publishing the mark schemes for the May/June 207 series for most Cambridge IGCSE, Cambridge International A and AS Level and Cambridge Pre-U components, and some Cambridge O Level components. IGCSE is a registered trademark. This document consists of 9 printed pages. UCLES 207 [Turn over

18 970/22 Cambridge International AS/A Level Mark Scheme May/June 207 (a) atomic number nucleon number number of electrons number of protons number of neutrons symbol Fe + (b)(i) EITHER mass of an atom / isotope relative / compared to /2 (the mass) of (an atom of) C-2 OR on a scale in which a C-2 (atom / isotope) has (a mass of exactly) 2 (units) 2 OR mass of one mol (of atoms) of an isotope relative / compared to /2 (the mass) of mol of C-2 OR on a scale in which one mol C-2 (atom / isotope) has a mass of (exactly) 2 g (b)(ii) ( ) + (80.22x) = x = Total: 6 UCLES 207 Page 2 of 9

19 970/22 Cambridge International AS/A Level Mark Scheme May/June 207 2(a) strong triple bond non-polar / no dipole 2(b)(i) Any 2 points covered correctly scores 2 marks Any point covered correctly scores mark nitrogen (and oxygen) from the air / atmosphere (react): high temperature (of internal combustion engine) / (engine) produces enough OR a lot of heat (energy) : (so) breaks (strong) bond(s) in nitrogen (and oxygen) : 2 2(b)(ii) reduction / decomposition of NO x using a catalyst / catalytic convertor 2NO 2 + 4CO 4CO 2 + N 2 OR 2NO + 2CO 2CO 2 + N 2 2(b)(iii) (acts as a homogeneous) catalyst OR oxidising agent SO 2 + NO 2 SO 3 + NO NO + ½O 2 NO 2 OR SO 3 + H 2 O H 2 SO 4 2(b)(iv) 2NO 2 + H 2 O HNO 2 + HNO 3 OR 4NO 2 + 2H 2 O + O 2 4HNO 3 2(c) fertiliser / nitrates dissolve in (river water) OR fertiliser / nitrates are washed / leached out / flows into (river water) UCLES 207 Page 3 of 9

20 970/22 Cambridge International AS/A Level Mark Scheme May/June 207 algal bloom / promote algal growth / explosion of plant growth AND EITHER sunlight is blocked out (preventing photosynthesis) / plants can no longer carry out photosynthesis (and die) OR bacteria break down or decay dead organisms / plants / algae drop in oxygen (concentration) Total: 3 UCLES 207 Page 4 of 9

21 970/22 Cambridge International AS/A Level Mark Scheme May/June 207 3(a) (+) 03 3(b)(i) general shape of the curve and peak are displaced to right of original and starts at origin the peak is lower and curve crosses once only finishing above original 3(b)(ii) rate increases AND correct explanation in terms of more collisions at higher T area above Ea is greater / more molecules with E Ea higher frequency of successful collisions OR more successful collisions per unit time / higher chance of successful collisions per unit time / higher proportion of successful collisions per unit time 3(b)(iii) increases (%) decomposition (of HBr) (increasing T) shifts equilibrium to the right / in the forward direction / endothermic direction / towards H 2 + Br 2 3(b)(iv) to oppose the change or oppose the increase in temperature OR to absorb (additional) energy / heat OR to decrease the temperature H-I bond strength less than H-Br OR less energy needed to break H-I ora I (atom) is big(ger) (than Br) OR I (atom) has more shielding (than Br) ora Br (atom) has greater (%) orbital / outer shell overlap OR attraction (of nucleus in iodine) for shared (pair of) electrons is weak(er) OR attraction (of nucleus in iodine) for bonding pair (or electrons) is weak(er) ora UCLES 207 Page 5 of 9

22 970/22 Cambridge International AS/A Level Mark Scheme May/June 207 3(c)(i) H 2 = 0.05 (mol) HCl = 0.27 (mol) 3(c)(ii) 3(d)(i) HCl = 9/0 AND xh 2 = /20 AND Cl 2 = /20 OR HCl = 0.9(0) AND H 2 = 0.05 AND Cl 2 = 0.05 ph2 pcl2 (K p =) 2 phcl 3(d)(ii) equal number of moles (of gas) on either side (of equation) / (total) pressure cancels 3(d)(iii) Total: 8 UCLES 207 Page 6 of 9

23 970/22 Cambridge International AS/A Level Mark Scheme May/June 207 4(a)(i) (A = ) 4(a)(ii) (A / straight chain) has strong(er) (temporary dipole-) induced dipole (attractions) ora (because A / straight chain has) bigger (surface) area / more (points of) contact (in unbranched isomer) ora OR (so) more energy required to break the intermolecular forces ora 4(a)(iii) CH 3 CHCHCH 3 OR CH 3 CH=CHCH 3 4(a)(iv) No rotation / restricted / limited rotation of C=C / (carbon) double bond One (of the two) methyl groups / one (of the two) H (atoms) is on each C (of C=C) 4(a)(v) arrow from the C=C double bond drawn to the bromine dipole on Br 2 in correct orientation AND arrow from the Br-Br bond to the Br δ correct carbocation / bromonium ion from the structure with C=C drawn 4(a)(vi) Br with lone pair, negative charge AND arrow from lone pair to the carbon atom of intermediate OR using both arrows shown (in alternative diagram) electrons in pi bond induce it (the dipole) OR (high) electron density in pi bond / double bond / C=C repels electrons (away from nearest Br) OR polarised by (high) electron density in pi bond / double bond / C=C UCLES 207 Page 7 of 9

24 970/22 Cambridge International AS/A Level Mark Scheme May/June 207 4(b)(i) C = (2-)methylpropan-2-ol / (CH 3 ) 3 COH / any unambiguous structure D = (2-)methylpropan--ol / (CH 3 ) 2 CHCH 2 OH / any unambiguous structure E = (2-)methylpropanoic acid /(CH 3 ) 2 CHCO 2 H / any unambiguous structure 4(b)(ii) 2C 4 H 8 O 2 + Na 2 CO 3 2C 4 H 7 O 2 Na + H 2 O + CO 2 4(c)(i) triiodomethane 4(c)(ii) F = CH 3 CH 2 CH 2 COCH 3 G = C 2 H 5 CH(CH 3 )CHO 4(c)(iii) a (tetrahedral) atom with four different groups / atoms / substituents attached OR a carbon (atom) with four different groups / atoms / substituents attached 4(d)(i) H C=O (group / bond) AND O H (group / bond) I C=O (group / bond) AND C H (group / bond) UCLES 207 Page 8 of 9

25 970/22 Cambridge International AS/A Level Mark Scheme May/June 207 4(d)(ii) H = ethanoic acid I = methyl methanoate Total: 23 UCLES 207 Page 9 of 9

26 Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level CHEMISTRY 970/23 Paper 2 AS Level Structured Questions May/June 207 MARK SCHEME Maximum Mark: 60 Published This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of the examination. It shows the basis on which Examiners were instructed to award marks. It does not indicate the details of the discussions that took place at an Examiners meeting before marking began, which would have considered the acceptability of alternative answers. Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for Teachers. Cambridge will not enter into discussions about these mark schemes. Cambridge is publishing the mark schemes for the May/June 207 series for most Cambridge IGCSE, Cambridge International A and AS Level and Cambridge Pre-U components, and some Cambridge O Level components. IGCSE is a registered trademark. This document consists of 8 printed pages. UCLES 207 [Turn over

27 970/23 Cambridge International AS/A Level Mark Scheme May/June 207 (a) (molecules / isomers with) the same molecular formula / same number of atoms of each element different structural / displayed formulae / different arrangement of bonds (b)(i) 4 (b)(ii) 6 (b)(iii) molecular = C 4 H 8 empirical = CH 2 using alternative supplied data molecular = C 6 H 2 empirical = CH 2 UCLES 207 Page 2 of 8

28 970/23 Cambridge International AS/A Level Mark Scheme May/June 207 (b)(iv) alternative using supplied data: any two (b)(v) correct conversions of data to SI / consistent units P = ; V = ; T = 30 calculation of n ( = pv / RT) n= calculation of mass m ( = n M r ) AND answer correct to 3sf m = = (g) Alternative answer for using C 6 H 2 : m = = (g) Total: UCLES 207 Page 3 of 8

29 970/23 Cambridge International AS/A Level Mark Scheme May/June 207 2(a)(i) halogen colour state chlorine yellow / green gas bromine red / brown / orange liquid iodine grey / black solid 2 2(a)(ii) increasing number of electrons (gives) increasing strength of van der Waals / id-id forces / London / dispersion forces 2(b) oxidising power decreases down the group. ora ability to accept electrons decreases (down the group) ora because (outer shell experiences) more shielding OR increased distance from nucleus (to outer shell) (outweighs the increasing nuclear charge down the group) ora 2(c)(i) solid sodium chloride: steamy / misty / white fumes 2(c)(ii) solid sodium iodide: purple fumes (conc sulfuric) not powerful enough oxidising agent (to oxidise chloride) OR chloride not powerful enough reducing agent (to reduce sulfuric acid) iodide reduces sulfuric acid OR iodide / I is oxidised OR sulfuric acid oxidises iodide UCLES 207 Page 4 of 8

30 970/23 Cambridge International AS/A Level Mark Scheme May/June 207 2(c)(iii) 2NaBr + 2H 2 SO 4 Br 2 + SO 2 + Na 2 SO 4 + 2H 2 O OR NaBr + H 2 SO 4 NaHSO 4 + HBr AND 2HBr + H 2 SO 4 Br 2 + SO 2 + 2H 2 O OR 2NaBr + H 2 SO 4 Na 2 SO 4 + 2HBr AND 2HBr + H 2 SO 4 Br 2 + SO 2 + 2H 2 O 2 2(d)(i) AgI (and AgCl solid) / silver ions reacting with iodide ions 2(d)(ii) AgCl (precipitate) dissolves (in ammonia) owtte Total: 5 3(a)(i) (enthalpy / energy change) when one mole of a compound is formed from its elements in their standard states / standard conditions 3(a)(ii) ( H r = H f products Σ H f reactants) 96 =2 H f SO 3 ( ) 2 H f SO 3 = 96 + ( ) = H f SO 3 = (kj mol ) 3(b)(i) Mark to right of original E a UCLES 207 Page 5 of 8

31 970/23 Cambridge International AS/A Level Mark Scheme May/June 207 3(b)(ii) 2 marks for any two points: Benefit of using a catalyst in terms of increasing rate or economic benefit i.e. (less heat required) Creates alternative pathway with lower E a More molecules with E > E a 2 3(b)(iii) (rate) increases AND correct explanation in terms of more collisions 3(c)(i) more successful collisions per unit time / higher chance of successful collisions per unit time / higher proportion of successful collisions per unit time (yield) increases and shifts equilibrium to the right / in the forward direction / towards SO 3 / towards the product / in exothermic direction to oppose the change or oppose the increase in pressure / fewer molecules on RHS so eqm moves to right (to oppose change) SO 2 = 0.0 (mol) AND SO 3 = 0.99 (mol) 3(c)(ii) n TOT =.505 3(d)(i) po 2 = (0.505 /.505) = (Pa) ( K p = ) pspoo23pso 222 3(d)(ii) Pa Total: 7 UCLES 207 Page 6 of 8

32 970/23 Cambridge International AS/A Level Mark Scheme May/June 207 4(a) cracking 4(b) In any order CH 2 =CHCH 2 CH 3 / CH 2 CHCH 2 CH 3 / CH 2 CHC 2 H 5 AND CH 3 CH=CHCH 3 / CH 3 CHCHCH 3 AND (CH 3 ) 2 C=CH 2 / (CH 3 ) 2 CCH 2 4(c)(i) (different) molecules with the same (molecular and) structural formula (due to) different arrangement in space caused by C=C / double bond 4(c)(ii) H H H 3 C C C CH 3 Hδ+ Brδ H H 3 C C + C CH 3 Br - H H arrow from the C=C double bond drawn to the H dipole on H Br in correct orientation AND arrow from the H-Br bond to the Br δ correct carbocation from the structure with C=C drawn Br with lone pair, negative charge AND arrow from lone pair to the positively charged carbon atom of intermediate UCLES 207 Page 7 of 8

33 970/23 Cambridge International AS/A Level Mark Scheme May/June 207 4(d)(i) a (tetrahedral) atom with four different groups / atoms / substituents attached OR a carbon (atom) with four different groups / atoms / substituents attached 4(d)(ii) but ene 4(d)(iii) H 2 CCH 3 H 3 CCH 2 Br C H CH 3 H 3 C H C Br One 3D structure of 2 bromobutane which must have 2 bonds shown the same and two different, i.e. three bond types altogether, e.g. two solid lines, one wedge and one dash. If two bonds are drawn in the plane of the paper, i.e. single solid lines, they must not be at 80 degrees to each other. Second structure either mirror of first OR all bonds drawn the same with position of two groups swapped. 4(d)(iv) intermediate / (secondary carbo) cation from X is more stable ora OR charge density of C + (of the intermediate of X) is reduced (due to) electron-releasing character / (positive) inductive effect of alkyl groups / / due to electron releasing alkyl group 4(e)(i) (2 )methylpropene / (2 )methylprop ene 4(e)(ii) H H C H H Br C H H C H H C H H H 2 H H C C C H H H H C H Br Total: 7 UCLES 207 Page 8 of 8

34 Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level CHEMISTRY 970/3 Paper 3 Advanced Practical Skills May/June 207 MARK SCHEME Maximum Mark: 40 Published This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of the examination. It shows the basis on which Examiners were instructed to award marks. It does not indicate the details of the discussions that took place at an Examiners meeting before marking began, which would have considered the acceptability of alternative answers. Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for Teachers. Cambridge will not enter into discussions about these mark schemes. Cambridge is publishing the mark schemes for the May/June 207 series for most Cambridge IGCSE, Cambridge International A and AS Level and Cambridge Pre-U components, and some Cambridge O Level components. IGCSE is a registered trademark. This document consists of 8 printed pages. UCLES 207 [Turn over

35 970/3 Cambridge International AS/A Level Mark Scheme May/June 207 (a) I: All the following data is recorded rough titration: both burette readings and the titre initial and final burette readings for two (or more) accurate titrations Headings and units are not required for this mark II: Titre values recorded for accurate titrations, and Appropriate headings and units in the accurate titration table initial / start (burette) reading / volume final / end (burette) reading / volume titre or volume used / added (not difference ) unit: / cm 3 or (cm 3 ) or in cm 3 (for each heading) or cm 3 unit given for each volume recorded III: All accurate burette readings are recorded to the nearest 0.05 cm 3. The requirement to record to 0.05 applies to burette readings, including 0.00 cm 3 (if this was the initial reading), but it does not apply to the titre. 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 greater than 50.(00) IV: Final uncorrected titre is within 0.0 cm 3 of any previous uncorrected accurate titre. UCLES 207 Page 2 of 8

36 970/3 Cambridge International AS/A Level Mark Scheme May/June 207 Examiner rounds any accurate burette readings to the nearest 0.05 cm 3, check subtractions and then select the best titres using the hierarchy: identical titres then accurate titres within 0.05 cm 3, then accurate titres within 0.0 cm 3, etc. These best titres should be used to calculate the mean titre, expressed to nearest 0.0 cm 3. Examiner compares candidate s tire value with that of the Supervisor. Award V, VI and VII if δ 0.30 (cm 3 ) Award V and VI if 0.30 < δ 0.50 Award V, only, if 0.50 < δ 0.80 (b) Candidate calculates the mean correctly. Candidate must take the average of two (or more) titres that are within a total spread of not more than 0.20 cm 3. 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 0.0 cm 3. (e.g cm 3 must be rounded to cm 3 ) UCLES 207 Page 3 of 8

37 970/3 Cambridge International AS/A Level Mark Scheme May/June 207 (b) Two special cases, where the mean need not be to 2 dp: Allow mean expressed to 3 dp only for or (e.g cm 3 ) Allow mean if expressed to dp, if all accurate burette readings were given to dp and the mean is exactly correct. (e.g and 26.2 = 26. is allowed) (e.g and 26. = 26. is wrong should be 26.05) Do not award this mark if: The rough titre was used to calculate the mean. The candidate did only one accurate titration. Burette readings were incorrectly subtracted to obtain any of the accurate titre values. All burette readings used to calculate the mean were recorded as integers Note: the candidate s mean will sometimes be marked correct even if it was different from the mean calculated by the Examiner for the purpose of assessing accuracy. (c)(i) No of moles of thiosulfate used = 0.0 mean titre / 000 (expressed to 3 or 4 sig fig) (c)(ii) + (iii) (c)(iv) Equation balanced I 2 + 2Na 2 S 2 O 3 Na 2 S 4 O 6 + 2NaI and no of moles of I 2 = 0.5 ans. in (i) Correct answer, No of moles of copper(ii) ions = 2 answer (iii) (expressed to 3 or 4 sig fig) (c)(v) M r = 26.0 / ans (iv) 25 / 000 Total: 2 UCLES 207 Page 4 of 8

38 970/3 Cambridge International AS/A Level Mark Scheme May/June 207 2(a) I: Table of data, to include: Unit covering all weighings, or given for each weighing No repeat headings (i.e. not two lists of weighings) Appropriate headings for the three weighings: Mass of crucible and lid Mass of crucible, lid and FA 5 (or contents before heating ) Mass of crucible, lid and residue / CuO / contents after heating II: Weighings recorded Six weighings recorded in the space provided. All weighings recorded to same number of decimal places (one or more) Label/heading to indicate which is Expt and Expt 2 III: Both masses of FA 5 and residue, correctly subtracted Masses of FA 5 used recorded on page 4, correctly subtracted Masses of FA 5 used were between g and g Masses of residue recorded on page 4, correctly subtracted For assessment of accuracy, examiner must check and correct (if necessary) the masses of FA 5 used and of CuO obtained by the supervisor and by the candidate for Experiment. Examiner works out the ratio mass of FA5 / mass of CuO for the supervisor (2 dp) Examiner works out the ratio (mass FA 5: mass CuO) for the candidate (2 dp) Examiner calculates δ the difference between these two ratios. Award IV and V if δ 0.08 Award IV if 0.08 < δ 0.5 VI: Observations made during heating Solid goes black / black residue (formed) or reference to blue/green flame 2 2(b)(i) No of moles CuO = mass of residue / 79.5 Answer must be correct and expressed to 3 or 4 sig fig UCLES 207 Page 5 of 8

39 970/3 Cambridge International AS/A Level Mark Scheme May/June 207 2(b)(ii) No of moles of FA 5 = answer (i) / 2 M r = mass of FA 5 used / no of moles of FA 5 2(b)(iii) M r = mass of FA5 used in Expt / mass of residue (CuO) 2(b)(iv) M r of FA 5 calculated from A r values = 239 2(b)(v) Candidate should correctly calculate the 2.5% of M r in (iv) = 5.98 / 6.0, and make a correct statement about the accuracy of the accepted formula, based on their result(s). or correctly calculate % difference for their result(s) from M r in (iv) and correct comment 2(c)(i) heat (crucible and residue) to constant mass heat more gently for longer period cool in a desiccator to ensure that decomposition (of FA 5) is complete or to ensure that all the residue is CuO to prevent escape of dust / smoke / solid (during heating) 2(c)(ii) Larger masses have lower percentage error in weighing Total: 4 UCLES 207 Page 6 of 8

40 970/3 Cambridge International AS/A Level Mark Scheme May/June 207 FA 6 is Cu(NO 3 ) 2 ; FA 7 is FeCl 3 3(a)(i) melts or dissolves or blue liquid / solution formed condensation or steam / vapour produced black residue / solid brown gas / fumes gas / oxygen relights a glowing spill 2 4 or 5 observations correct = 2 marks 2 or 3 observations correct = mark 3(a)(ii) FA 6 is Cu(NO 3 ) 2 3(b)(i) with KI, FA 7 gives a brown / red-brown / red / orange solution with starch, blue / blue-black / dark colour with FA 6, blue precipitate (formed) on heating, (blue precipitate) turns black With FA 7, red-brown / brown / rust ppt. (formed ) With FA 6, no reaction / no change / no ppt. With FA 7, white precipitate formed With FA 6, (pale) blue precipitate, then deep/dark blue (solution) with excess With FA 7, red-brown / brown / rust precipitate (forms) Mg test Both observations correct With FA 6, brown / black precipitate / solid formed or blue colour fades / disappears With FA 7, fizzing / bubbling / effervescence Test for hydrogen: (gas) pops with lighted splint UCLES 207 Page 7 of 8

41 970/3 Cambridge International AS/A Level Mark Scheme May/June 207 3(b)(ii) FA 7 is acidic, because it fizzes / produces hydrogen with magnesium 3(b)(iii) Fe 3+ (aq) + 3OH (aq) Fe(OH) 3 (s) 3(b)(iv) Redox because iodine was produced (from iodide ions) 3(b)(v) You can t be certain about the colour of the precipitate (with AgNO 3 ) due to the coloured solution / colour of FA 7. or You can t be sure whether the precipitate with AgNO 3 is white / AgCl or cream / AgBr 3(b)(vi) Ammonia would react with the Fe 3+ ions in FA 7 (masking the effect of ammonia on AgCl) or The cation in FA 7 gives a precipitate with ammonia (so the precipitate of AgCl would not appear to dissolve). Total: 4 UCLES 207 Page 8 of 8

42 Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level CHEMISTRY 970/32 Paper 3 (Advanced Practical Skills 2) May/June 207 MARK SCHEME Maximum Mark: 40 Published This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of the examination. It shows the basis on which Examiners were instructed to award marks. It does not indicate the details of the discussions that took place at an Examiners meeting before marking began, which would have considered the acceptability of alternative answers. Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for Teachers. Cambridge will not enter into discussions about these mark schemes. Cambridge is publishing the mark schemes for the May/June 207 series for most Cambridge IGCSE, Cambridge International A and AS Level and Cambridge Pre-U components, and some Cambridge O Level components. IGCSE is a registered trademark. This document consists of 9 printed pages. UCLES 207 [Turn over

43 970/32 Cambridge International AS/A Level Mark Scheme May/June 207 (a) I Initial and final burette readings and volume added recorded for rough titre and accurate titre details tabulated. [minimum 2 2 boxes with relevant information] II Initial and final burette readings recorded and volume of FB 2 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 2 added/used or titre and Units: (cm 3 ) or / cm 3 or in cm 3 [or cm 3 by every entry] III All accurate burette readings are recorded to the nearest 0.05 cm 3 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 greater than 50(.00) IV The final accurate titre recorded is within 0.0 cm 3 of any other accurate titre. UCLES 207 Page 2 of 9

44 970/32 Cambridge International AS/A Level Mark Scheme May/June 207 (a) For assessment of accuracy (Q) marks, each Examiner should round any accurate burette readings to the nearest 0.05 cm 3, check subtractions and then select the best titres for supervisor and candidate using the hierarchy: two identical; titres within 0.05 cm 3 ; titres within 0. cm 3 ; etc. These best titres should be used to calculate the mean titre, expressed to the nearest 0.0 cm 3. The candidate s titre is compared to the supervisor s titre and δ calculated. (b) V, VI and VII Award V, VI and VII for δ 0.20 cm 3 Award V and VI for 0.20 cm 3 < δ 0.30 cm 3 Award V for 0.30 cm 3 < δ 0.50 cm 3 Check mean titre is correctly calculated from clearly selected values (ticks or working). Candidate must average two (or more) titres where the total spread is 0.20 cm 3. Working must be shown or ticks must be put next to the two (or more) accurate readings selected. The mean should normally be quoted to 2 dp rounded to the nearest 0.0. [e.g must be rounded to 26.67] Two special cases where the mean may not be to 2 dp: allow mean to 3 dp only for or e.g ; allow mean to dp if all accurate burette readings were given to dp and the mean is exactly correct. [e.g and 26.2 = 26. is correct but 26.0 and 26. = 26. is incorrect.] Do not award this mark if: the rough titre was used to calculate the mean; candidate carried out only accurate titration; burette readings were incorrectly subtracted to obtain any of the accurate titre values; all burette readings (resulting in titre values used in calculation of mean) are integers. Note: the candidate s mean will sometimes be marked as correct even if it is different from the mean calculated by the examiner for the purpose of assessing accuracy. 3 (c)(i) Correctly calculates 0.00 x = 2.5(0) 0 3 UCLES 207 Page 3 of 9

45 970/32 Cambridge International AS/A Level Mark Scheme May/June 207 (c)(ii) Correctly calculates x 000 ( b) to 3 or 4 sf (c)(iii) Correct expression 2.6 (ii) (c)(iv) Anion in FB = CHCl 2 COO (allow ecf: for candidate s answer to (iii)) CH 3 COO : 77 CH 2 ClCOO : CHCl 2 COO : 2 46 CCl 3 COO : 46.5 (d)(i) Conc NaOH lower = > titre smaller = > smaller M r (d)(ii) No effect on identification unless closer to smaller mass acid or (different M r may lead to the) identification of a different acid with matching / close to M r Total: 4 2(a) I Unambiguous headings and correct units tabulated for all 6 thermometer readings, mean temps, and Ts II All thermometer readings recorded to 0.5 C and Ts correctly calculated and Mean temperatures correctly calculated to nearest.5 C or to or 2 dp Award III if candidate Ts within.5 C Award III and IV if candidate Ts within.0 C 2(b)(i) Correctly calculates n acid = 0.05(0) mol and n NaOH = mol UCLES 207 Page 4 of 9

46 970/32 Cambridge International AS/A Level Mark Scheme May/June 207 2(b)(ii) Correctly calculates T to minimum 2 sf 2(b)(iii) Correct expression ( ii) 000 x (b)(iv) +(v) 2 mol NaOH in (i) or 0.09(0) in (iv) and 00 x 4.2 x T ( 2) Correctly uses in (v) 000 x iv ( ) Negative signs shown in (iii) and (v) and final answers to 2 4 sf in (ii), (iii) & (v) 2(c)(i) % error in vol of FB 3 = 0.5 x =.(0)% % error in vol of FB 4 = 2 x 0.25 x = 2.(0)% 2(c)(ii) Use a burette / pipette for volume measurements / instead of a measuring cylinder or Add a lid to reduce heat loss (by convection) / to reduce convection or Use thermometer reading to 0.2 C / smaller divisions / calibrations / more sensitive Total 2 UCLES 207 Page 5 of 9

47 970/32 Cambridge International AS/A Level Mark Scheme May/June 207 FB 5 is CH 3 COOH; FB 6 is HCl; FB 7 is HNO 3 ; FB 8 is CuSO 4 (aq); FB 9 is Na 2 edta 3(a)(i) Selects Na 2 CO 3 / Mg Effervescence / bubbling / fizzing greater / faster with FB 6 FB 5 is the weak acid (ora) with some evidence 3(a)(ii) no reaction / no ppt / no change with Ag + and not needed with Ba 2+ (do not allow no change unless there is no evidence of ammonia in 2nd test) Effervescence alone is not evidence so would expect no change. Effervescence / gas / NH 3 and turns (damp red) litmus blue FB 7 is nitric acid from some evidence (can be effervescence in (ii)) UCLES 207 Page 6 of 9

48 970/32 Cambridge International AS/A Level Mark Scheme May/June 207 3(b) (i) (vi) See below 6 Expected observations test observation mark (i) + Na 2 CO 3 (ii) + KI then (pale) blue ppt (Allow blue-green / green-blue / turquoise / cyan) Yellow-brown / brown (not orange) Na 2 S 2 O 3 white / off-white ppt and soluble in excess (iii) + c.hcl and (blue) (solution) turns green (shade greener) (iv) + H 2 O (green) (solution) turns (pale) blue (shade bluer) (v) + NH 3 (in excess) forming dark/deep blue solution or solution much darker than (iv) (vi) + edta (solution) more blue / darker blue than (iv) UCLES 207 Page 7 of 9

49 970/32 Cambridge International AS/A Level Mark Scheme May/June 207 3(vii) FB 8 contains Cu 2+ /copper(ii) 3(viii) Cu 2+ (aq) + CO 3 2 (aq) CuCO 3 (s) Allow 2Cu 2+ (aq) + 4I (aq) 2CuI(s) + I 2 (aq or s) Allow Cu 2+ (aq) + 2OH (aq) 2Cu(OH) 2 (s) Total: 4 UCLES 207 Page 8 of 9

50 970/32 Cambridge International AS/A Level Mark Scheme Mark allocation May/June 207 Skill Minimum mark allocation Breakdown of marks Statement Minimum Marks Question Question 2 Question 3 Total mark Manipulation, measurement and observation (MMO) 2 marks [7] Successful collection of data and observations Quality of measurements and observations C Q Decisions relating to measurements of observations De 2 2 Presentation of data and observations (PDO) 6 marks [7] Recording data or observations Display of calculation and reasoning R 2 2 Di Data layout L 2 2 Analysis, conclusions and evaluation (ACE) 0 marks [6] Interpretation of data or observations and identifying sources of error I Drawing conclusions Con Suggesting improvements Imp Total UCLES 207 Page 9 of 9

51 Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level CHEMISTRY 970/33 Paper 3 Advanced Practical Skills May/June 207 MARK SCHEME Maximum Mark: 40 Published This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of the examination. It shows the basis on which Examiners were instructed to award marks. It does not indicate the details of the discussions that took place at an Examiners meeting before marking began, which would have considered the acceptability of alternative answers. Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for Teachers. Cambridge will not enter into discussions about these mark schemes. Cambridge is publishing the mark schemes for the May/June 207 series for most Cambridge IGCSE, Cambridge International A and AS Level and Cambridge Pre-U components, and some Cambridge O Level components. IGCSE is a registered trademark. This document consists of 0 printed pages. UCLES 207 [Turn over

52 970/33 Cambridge International AS/A Level Mark Scheme May/June 207 (a) I Correct headings The following data are recorded in the space provided mass of container with FA 2 mass of (empty) container mass of FA 2 Mass must be stated for each piece of data. Unit / g (etc.) must be given for each piece of data. Subtraction for mass of FA 2 used must be correct. II All the following data are recorded 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 Appropriate headings and units in the accurate titration table initial / start (burette) reading / volume final / end (burette) reading / volume titre or volume / FA and used / added unit: / cm 3 or (cm 3 ) or in cm 3 (for each heading) or cm 3 unit given for each volume recorded IV All accurate burette readings are recorded to the nearest 0.05 cm 3. The requirement to record to 0.05 applies to burette readings, including 0.00 cm 3 (if this was the initial reading), but it does not apply to the titre. This mark is not awarded if: 50(.00) is used as an initial burette reading more than one final burette reading is 50.(00) any burette reading is greater than 50.(00) V The final accurate titre recorded is within 0.0 cm 3 of any other accurate titre. Do not include a reading if it is labelled rough. Do not award the mark if any accurate burette readings (apart from initial 0 cm 3 ) are given to zero dp. UCLES 207 Page 2 of 0

53 970/33 Cambridge International AS/A Level Mark Scheme May/June 207 For assessment of accuracy (Q) marks, each Examiner should round any burette readings to the nearest 0.05 cm 3, check subtractions and 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 cm 3, then two (or more) accurate titres within 0.0 cm 3, etc. These best titres should be used to calculate the mean titre, expressed to nearest 0.0 cm 3. Calculate the candidate s ratio to dp, as shown below. Ratio = correct mean titre correct mass Calculate the difference (δ) between the candidate s ratio and the supervisor s ratio. Accuracy marks are awarded as follows. (a) Award VI, VII and VIII if δ 0.2 (cm 3 g ) Award VI and VII if 0.2 < δ 0.4 Award VI, only, if 0.4 < δ 0.6 Spread penalty: if the two best (corrected) titres used by the Examiner were 0.50 cm 3 apart, maximum 2 accuracy marks. If only a rough titration is shown, award Q marks based on that, maximum 2 accuracy marks. UCLES 207 Page 3 of 0

54 970/33 Cambridge International AS/A Level Mark Scheme May/June 207 (b) Candidate calculates the mean correctly. Candidate must take the average of two (or more) titres that are within a total spread of not more than 0.20 cm 3. 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 0.0 cm 3. (e.g cm 3 must be rounded to cm 3 ) Two special cases, where the mean need not be to 2 dp: Allow mean expressed to 3 dp only for or (e.g cm 3 ) Allow mean if expressed to dp, if all accurate burette readings (apart from initial 0) were given to dp and the mean is exactly correct. (e.g and 26.2 = 26. is allowed) (e.g and 26. = 26. is wrong should be 26.05) This mark is not awarded if: The rough titre was used to calculate the mean. The candidate did only one accurate titration. Burette readings were incorrectly subtracted to obtain any of the accurate titre values. All burette readings used to calculate the mean were recorded as integers Note: the candidate s mean will sometimes be marked correct even if it was different from the mean calculated by the Examiner for the purpose of assessing accuracy. (c)(i) No of moles of H 2 SO 4 used = 0.05(0) (b) / 000 to minimum 2 sf (c)(ii) and (c)(iii) 2NaHCO 3 + H 2 SO 4 Na 2 SO 4 + 2CO 2 + 2H 2 O and No of moles of NaHCO 3 = 2 answer (i) UCLES 207 Page 4 of 0

55 970/33 Cambridge International AS/A Level Mark Scheme May/June 207 (c)(iv) Mass of NaHCO 3 = answer (iii) 0 84 (c)(v) (c)(vi) % = answer (iv) / mass of FA 2 used 00 All answers attempted in (i), (iii), (iv) & (v) are shown to 3 or 4 sf Minimum 3 answers attempted to gain the mark Any one of the following answers. the impurity does not react with (sulfuric) acid / FA / NaHCO 3 the impurity is not alkaline / acidic the impurity is neutral (c)(vii) % error (= 0. / ) = 0.04% Total: 6 UCLES 207 Page 5 of 0

56 970/33 Cambridge International AS/A Level Mark Scheme May/June 207 2(a) I Four weighings recorded and correct headings given and mass of FA 4 used and mass of residue recorded (Mass of) crucible, (lid) (Mass of) crucible, (lid) and FA 4 (or 'contents before heating) (Mass of) crucible, (lid) and contents / residue / FA 4 after (first) heating (Mass of) crucible, (lid) and contents / residue / FA 4 after re-heating (Mass of) FA 4 (Mass of) residue / FA 5 / contents after heating If mass not written then g must be with each entry. Use of lid must be consistent. II All weighings recorded to same decimal places (one or more). Third and fourth weighings are within 0.05 g of each other (or both equal if a one decimal place balance was used) Mass of FA 4 and FA 5 / residue must be correctly subtracted. UCLES 207 Page 6 of 0

57 970/33 Cambridge International AS/A Level Mark Scheme May/June 207 2(a) 2(b)(i) and 2(b)(ii) 2(b)(iii) III and IV: For assessment of accuracy, examiner must check and correct (if necessary) the masses of FA 4 used and of residue (smaller mass) obtained by the supervisor and by the candidate. Work out ratio mass of FA4 / mass of residue for the supervisor (2 dp) Work out ratio mass of FA4 / mass of residue for candidate (2 dp) Calculate the difference (δ) between these two ratios. Award III and IV if δ 0.05 Award III if 0.05 < δ 0.0 (i) Mass NaHCO 3 = ( % purity from (c)(v) / 00 ) mass of FA 4 used and (ii) Mass impurity = mass of FA 4 answer (i) or mass impurity = % impurity / 00 x mass FA 4 Mass of decomposition solid = mass of residue (FA 5) from table mass of impurity (ii) and expressed to 2, 3 or 4 sig fig or mass of decomposition solid = mass of NaHCO 3 mass lost on heating [(i) (mass FA 4 mass FA 5)] 2 2(b)(iv) Mass of residue obtained = answer (iii) 84 / answer (i) UCLES 207 Page 7 of 0

58 970/33 Cambridge International AS/A Level Mark Scheme May/June 207 2(b)(v) If correct, (84 g) NaHCO 3 would give 40 g residue / NaOH (owtte) or mole ratio :.3 (so not :) or Answers could refer to mass / moles of CO 2 2(c)(i) Lid reduces / stops absorption of water (vapour) by solid / residue / FA 5 while cooling 2(c)(ii) 2(d)(i) Repeat the experiment and ignore anomalous results / to obtain concordant / consistent results or cool in a desiccator or use larger mass of FA 4 / contents / solid Any two observations required fizzing / effervescence / bubbling gas turns limewater milky / chalky / cloudy white / white ppt solid dissolves / colourless solution forms rapid/brisk effervescence = 2 observations 2(d)(ii) FA 5 contains carbonate ion / CO 3 2 and reference to fizzing (with acid) or to CO 2 liberated (with acid) or positive limewater test or correct equation 2(d)(iii) 2NaHCO 3 (s) H 2 O(g) + CO 2 (g) + Na 2 CO 3 (s) 2(d)(iv) (From equation) 84 g NaHCO 3 should give g residue (= 53 g) and gives a (sensible) comment based on student s 52.3 g Total: 4 UCLES 207 Page 8 of 0

59 970/33 Cambridge International AS/A Level Mark Scheme May/June 207 FA 6 is MnCl 2 ; FA 7 is Al 2 (SO 4 ) 3 3(a)(i) 3(a)(ii) Ba 2+ test: all observations correct FA 6 no change / no reaction / no ppt / solution stays colourless with both FA 7 white precipitate with Ba 2+ and white ppt (remains) / insoluble / no reaction with HNO 3 AgNO 3 test: both observations correct FA 6 white precipitate FA 7 no change / no reaction / solution stays colourless / no ppt Na 2 CO 3 test: both observations correct FA 6 no reaction / solid does not dissolve / no effervescence FA 7 fizzing / bubbling / effervescence / or gas / CO 2 turns limewater milky / chalky / cloudy white / (forms) white ppt FA 7 has lower ph and gas / CO 2 given off / it fizzes (more rapidly if fizzing with both) with sodium carbonate UCLES 207 Page 9 of 0

60 970/33 Cambridge International AS/A Level Mark Scheme May/June 207 3(b) Reagents: NaOH and NH 3 (names or correct formulae) Observations (3 mark) FA 6 + NaOH : off-white / buff / beige / light brown ppt FA 6 + NH 3 : off-white / buff / beige / light brown ppt FA 6 : both ppts insoluble in excess and darken / turn brown with either 3(c) FA 7 + NaOH : white ppt and soluble in excess FA 7 + NH 3 : white ppt and insoluble in excess Conclusions (one mark for each). FA 6 is MnCl 2 FA 7 is Al 2 (SO 4 ) 3 2 Total: 0 UCLES 207 Page 0 of 0

61 Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level CHEMISTRY 970/34 Paper 3 Advanced Practical Skills 2 May/June 207 MARK SCHEME Maximum Mark: 40 Published This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of the examination. It shows the basis on which Examiners were instructed to award marks. It does not indicate the details of the discussions that took place at an Examiners meeting before marking began, which would have considered the acceptability of alternative answers. Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for Teachers. Cambridge will not enter into discussions about these mark schemes. Cambridge is publishing the mark schemes for the May/June 207 series for most Cambridge IGCSE, Cambridge International A and AS Level and Cambridge Pre-U components, and some Cambridge O Level components. IGCSE is a registered trademark. This document consists of 7 printed pages. UCLES 207 [Turn over

62 970/34 Cambridge International AS/A Level Mark Scheme May/June 207 (a) I Mass (of Mg) with correctly displayed unit and all temperatures recorded Initial T must be between 0 45 C II All temperature readings to.5 ºC with at least one ending in.0 C and at least one ending in.5 C (b) Round any thermometer readings to the nearest.5 C Calculate T from T at 2 minutes to T max from the table. Compare with supervisor T. Award III if T within 2 C of supervisor Award III and IV if T within ºC of supervisor I Axes labelled (T on y-axis & t on x-axis). Scale chosen so that plotted points (and 0 C extra on y-axis) occupy more than half the available space in both directions. II Points plotted to within half a small square. Points that should be on lines must be on the line and points that should not be on lines must not be on lines. 2 III Two lines of best fit drawn one up to 2 minutes and the other after the reaction has occurred. IV Both lines extrapolated to 2½ minutes and vertical line drawn at 2½ minutes V Examiner to calculate T from candidate graph and award mark if within 0.5 C of candidate s T (c)(i) Correctly calculates energy evolved = T and answer to 2 4 sf. (c)(ii) Correct use of moles of magnesium = mass Mg from (a) / 24.3 Correct use of H = ( i) ( ) n Mg x 000 and answer must be negative (d) 2 masses, 4 thermometer readings and 2 temperature rises with correct units and unambiguous headings shown Examiner to calculate T longer piece / T shorter piece to 2 dp Award 2 marks if.80 to 2.20 Award mark if.70 to UCLES 207 Page 2 of 7