CHERRY HILL TUITION EDEXCEL CHEMISTRY A2 PAPER 32 MARK SCHEME Chemistry Advanced Level Paper 3 (9CH0/03) Question Number 1(a)(i) Acceptable Answer Additional Guidance suitable scale and axes labelled including units (1) all points plotted correctly (1) line of best fit (1) Mark Plotted points use at least half the available space in both directions ±½ a square Smooth line, no dot to dot NOTE: Points at t = 2000 and 6000 s should not be on the line of best fit. 3 1 CHERRY HILL TUITION EDEXCEL CHEMISTRY A2 PAPER 32 MARK SCHEME Question Number 1(a)(ii) Acceptable Answer Additional Guidance 1st order with respect to SO2Cl2 as half-life is constant values of two half-lives shown in graph in range 2000 – 2400 (s) (1) rate = k[SO2Cl2] Mark Example of graph (1) (1) 3 2 CHERRY HILL TUITION EDEXCEL CHEMISTRY A2 PAPER 32 MARK SCHEME Question Number 1(a)(iii) Acceptable Answer Additional Guidance Mark Example of calculation tangent drawn at 0.200 mol dm-3 SO2Cl2 (1) value of gradient (1) e.g. gradient = (-) 0.375/6400 = (-) 5.859 x 10−5 must be consistent with tangent shown on graph Question Number 1 (b) k = rate / 0.200 (1) value of k to 2 or 3 SF and units (1) Acceptable Answer k = 5.859 x 10−5/ 0.200 = 2.9 x 10−4 s−1 / 2.93 x 10−4 s−1 Allow TE from incorrect rate equation / allow TE from incorrect gradient Units must be consistent with rate equation 4 Additional Guidance Mark RDS Step 1 SO2Cl2 → SO2Cl + Cl (1) The RDS must involve one mol of SO2Cl2 Step 2 SO2Cl + Cl → SO2 + Cl2 (1) The equations taken together must add up to the overall equation SO2Cl2 → SO2 + Cl2 e.g. SO2Cl2 → SO2 + 2Cl 2Cl → Cl2 Ignore state symbols 2 (Total for Question 1 = 12 marks) 3 CHERRY HILL TUITION EDEXCEL CHEMISTRY A2 PAPER 32 MARK SCHEME Question Number 2(a) Question Number 2(b)(i) Question Number 2(b)(ii) Question Number 2(b)(iii) Acceptable Answer Additional Guidance Mark Example of calculation mass of C (1) mass of C = 2.83 x 12/44 = 0.772 g mass of H (1) mass of H = 0.693 x 2/18 = 0.077 g mass of oxygen and mols of C, H and O mass of oxygen = 0.952 – (0.772 + 0.077) = 0.103 g (1) ratio (1) empirical and use of molar mass to determine molecular formula (1) Acceptable Answer An answer that makes reference to the following point: contains benzene ring / arene Acceptable Answer is an aldehyde or ketone / is a carbonyl compound Acceptable Answer (Q is a) ketone Moles ratio C 0.772/12=0.0643 0.0643/0.0063=10 H 0.077/1=0.077 0.077/0.00643=12 O 0.103/16=0.0064 0.0064/0.0064=1 Empirical formula = C10H12O, this has mass =148 so molecular formula = C10H12O Additional Guidance 5 Mark Ignore comments about alkenes / unsaturated Additional Guidance 1 Mark Both aldehyde and ketone required for first alternative Additional Guidance 1 Mark Allow ‘not an aldehyde’ if first alternative given in (b)(ii) 1 4 CHERRY HILL TUITION EDEXCEL CHEMISTRY A2 PAPER 32 MARK SCHEME Question Number 2(c) Acceptable Answer Additional Guidance An answer that makes reference to the following points: Mark Award 1 mark for any structure of C10H12O which includes a benzene ring and a ketone e.g. (2) Chemical shift (1) peak at 7.5 ppm indicates a benzene ring and peak at 2.55 ppm indicates H on carbon adjacent to C=O and peak at 1.25 ppm indicates alkyl hydrogens Splitting pattern (2) Any 2 from 3: complex multiplet indicates a benzene ring septuplet indicates 6 equivalent protons on adjacent carbons doublet indicates one hydrogen on adjacent carbon Area under peak (2) Any 2 from 3: five H’s indicate C6H5 / monosubstituted benzene ring one H indicates one H on C next to carbonyl group six H’s indicates six H’s on two methyl groups 7 (Total for Question 2 = 15 marks) 5 CHERRY HILL TUITION EDEXCEL CHEMISTRY A2 PAPER 32 MARK SCHEME Question Number 3(a) (i) Acceptable Answer Mark An answer that makes reference to the following points: EITHER the solution of manganate(VII) ions OR Question Number 3(a) (ii) Additional Guidance (1) as distilled water/other solutions remaining in burette will dilute the solution of manganate(VII) ions (1) Distilled water, followed by the solution of manganate(VII) ions (1) So the distilled water will not dilute the solution of manganate(VII) ions (1) Acceptable Answer 2 Additional Guidance Mark An answer that makes reference to the following points: measure from the bottom of the meniscus (of the solution of manganate(VII) ions) (1) with eyes / head at same level (as meniscus) or ensuring the burette is vertical or use of white background to emphasise meniscus or ensuring funnel is removed from top of burette or ensuring there is no air bubble in the tip of the burette 2 (1) 6 CHERRY HILL TUITION EDEXCEL CHEMISTRY A2 PAPER 32 MARK SCHEME Question Number 3(a) (iii) Acceptable Answer Mark An explanation that makes reference to the following point: Question Number 3(b) Additional Guidance it will not change the amount / moles (of reactants) in the flask Acceptable Answer 1 Additional Guidance Mark Ignore state symbols H2C2O4 → 2CO2 + 2H+ + 2e− / C2O42- → 2CO2 + 2e− and MnO4− + 8H+ + 5e− → Mn2+ + 4H2O − + 2+ 5H2C2O4 + 2MnO4 + 6H → 2Mn + 10CO2 + 8H2O / 5C2O4 2MnO4− + 16H+ → 2Mn2+ + 10CO2 + 8H2O (1) 2- + Allow for 1 mark: 5H2C2O4 + 2MnO4− + 16H+ → 2Mn2+ + 10CO2 + 8H2O + 10H+ (2) Question Number 3(c) Acceptable Answer mean = 22.7 / 22.70 (cm3) 3 Additional Guidance (1) Mark 1 7 CHERRY HILL TUITION EDEXCEL CHEMISTRY A2 PAPER 32 MARK SCHEME Question Number 3(d) Acceptable Answer Additional Guidance Mark Example of calculation calculates amount of MnO4− (1) Amount of MnO4− = 22.7/1000 x 0.0105 = 2.3835 x 10−4 mol TE on mean in (c) 3 calculates amount of H2C2O4 (in 25 cm ) (1) Amount of H2C2O4 (in 25 cm3) = 2.3835 x 10−4 x 2.5 = 5.95875 x 10−4 mol TE on mol ratio in equation in (b) calculates amount of H2C2O4 (in 250 cm3) (1) Amount of H2C2O4 (in 250 cm3) = 5.95875 x 10−4 x 10 = 5.95875 x 10−3 mol calculates relative molecular mass of acid (1) Relative molecular mass of acid = 0.747 / 5.95875 x 10−3 = 125.4 calculates x (1) So relative mass of water of crystallisation = 125.4 – 90 = 35.4 35.4/18 = 1.97 so x = 2 Do not award x = 1.97 5 8 CHERRY HILL TUITION EDEXCEL CHEMISTRY A2 PAPER 32 MARK SCHEME Question Number 3 (e) Acceptable Answer Additional Guidance Mark An answer that makes reference to the following point: more MnO4− would show greater amount of H2C2O4 so molecular mass of xH2O would seem to be less, so value for x would be less (1) more MnO4− means lower molecular mass therefore mass of water of crystallisation is less so x is less than 2 (1) (1) or (1) 2 (Total for Question 3 = 16 marks) 9 CHERRY HILL TUITION EDEXCEL CHEMISTRY A2 PAPER 32 MARK SCHEME Question Number 4 (a) Question Number 4 (b) Acceptable Answer Mark An explanation that makes reference to the following point: production of CO2 (1) NaHCO3 + HCl → NaCl + CO2 + H2O (1) Acceptable Answer An answer that makes reference to the following points: drying agent Question Number 4 (c) Additional Guidance mixture becomes transparent / clear (from cloudy) Allow HCO3− + H+ → CO2 + H2O Ignore state symbols Additional Guidance (1) Allow to remove water (1) Allow drying agent stops clumping together Acceptable Answer Additional Guidance 2 Mark 2 Mark An explanation that makes reference to the following points: they will reduce the yield (1) as some of the 2-chloro-2-methylpropane will react with the water (and reform the alcohol) (1) Allow ‘as some of the 2-chloro-2-methylpropane might dissolve in the water’ 2 10 CHERRY HILL TUITION EDEXCEL CHEMISTRY A2 PAPER 32 MARK SCHEME Question Number 4(d) Acceptable Answer Additional Guidance breaking of CO bond in protonated alcohol (1) structure of intermediate (1) correct charge on carbon in intermediate (1) attack of chloride ion with lone pair (1) Mark Arrow must originate from bond and finish on oxygen Arrow must originate from lone pair on Cl− 4 (Total for Question 4 = 10 marks) 11 CHERRY HILL TUITION EDEXCEL CHEMISTRY A2 PAPER 32 MARK SCHEME Question Number *5 (a) Acceptable Answer Additional Guidance This question assesses a student’s ability to show a coherent and logically structured answer with linkages and fully-sustained reasoning. Marks are awarded for indicative content and for how the answer is structured and shows lines of reasoning. The following table shows how the marks should be awarded for indicative content. Number of Number of indicative marks awarded marking for indicative points seen marking points in answer 6 4 5–4 3 3–2 2 1 1 0 0 The following table shows how the marks should be awarded for structure and lines of reasoning. Mark Guidance on how the mark scheme should be applied: The mark for indicative content should be added to the mark for lines of reasoning. For example, an answer with five indicative marking points which is partially structured with some linkages and lines of reasoning scores 4 marks (3 marks for indicative content and 1 mark for partial structure and some linkages and lines of reasoning). If there are no linkages between points, the same five indicative marking points would yield an overall score of 3 marks (3 marks for indicative content and no marks for linkages). Number of marks awarded for structure of answer and sustained line of reasoning Answer shows a coherent and logical structure with linkages and fully sustained lines of reasoning demonstrated throughout Answer is partially structured with some linkages and lines of reasoning Answer has no linkages between points and is unstructured 2 1 0 12 CHERRY HILL TUITION EDEXCEL CHEMISTRY A2 PAPER 32 MARK SCHEME Indicative Content: technique A allows heating for a longer time period / technique B is suitable for a shorter time period technique A ensures oxidation / technique B may result in loss of reactant before oxidation technique A minimises release of flammable or harmful vapours / technique B allows release of flammable or harmful vapours, unless carried out in fume cupboard technique A involves more expensive equipment or is more complex to set up / technique B is simpler to set up or uses less expensive equipment as complete oxidation is not necessary to qualitatively show it is an alcohol that can be oxidised technique B is most appropriate as simpler / technique A is most appropriate as oxidation is guaranteed 6 13 CHERRY HILL TUITION EDEXCEL CHEMISTRY A2 PAPER 32 MARK SCHEME Question Number 5 (b) Acceptable Answer Additional Guidance Mark An explanation that makes reference to the following pairs: either no, as chloride ions could be oxidised by dichromate(VI) ions (reducing amount of oxidant / producing toxic chlorine) Eo values for dichromate(VI) and chloride ions being oxidised to chlorine are sufficiently close (even though Eo is negative = -0.03 V) for chlorine to be formed (1) yes, as reaction is dependent on H+ ions (not anions) (1) Eo value is negative (-0.03 V) (1) (1) or Question Number 5 (c) Acceptable Answer 2 Additional Guidance Mark 1 (Total for Question 5 = 9 marks 14 CHERRY HILL TUITION EDEXCEL CHEMISTRY A2 PAPER 32 MARK SCHEME Question Number 6 (a) Acceptable Answer Additional Guidance suitable extrapolation (1) ∆T in the range of 29 – 33(oC) (1) Mark Vertical at 3 minutes and smooth curve of best fit back from 10 minutes to 3 minutes 2 Question Number 6 (b) (i) Acceptable Answer Additional Guidance Mark An explanation that makes reference to the following point: as reaction is not instantaneous / takes time to release heat (1) so some heat is lost as mixture heats up 2 (1) 15 CHERRY HILL TUITION EDEXCEL CHEMISTRY A2 PAPER 32 MARK SCHEME Question Number 6 (b) (ii) Question Number 6 (c) Acceptable Answer Additional Guidance An explanation that makes reference to the following points: A greater surface area of zinc by using more finely powdered zinc (1) because it will increase the rate of reaction (1) Less time for heat loss Acceptable Answer Calculation of Q using Q = mc∆T Mark Additional Guidance (1) 2 Mark Using ∆T from (a) Example of calculation 25 x 4.18 x 30.5 = 3 187 (J) Allow 4.2 for 4.18 amount of CuSO4(aq) (1) = 25/1000 x 0.720 = 0.018 energy per mol = Q/0.018 (1) 3 187/0.018 ∆H = -Q/1000 kJ mol−1 (1) = −177 kJ mol−1 / −180 kJ mol−1 / −177 000 J mol−1 / −180 000 J mol−1 Use of 4.2 gives −178 kJ mol−1 Must have correct sign and units for 4th mark 4 16 CHERRY HILL TUITION EDEXCEL CHEMISTRY A2 PAPER 32 MARK SCHEME Question Number 6 (d) (i) Question Number 6 (d) (ii) Question Number 6 (d) (iii) Acceptable Answer Additional Guidance (217 – answer to (c) / 217) x 100 Example of calculation (217 – 177 / 217) x 100 = 18.4% Acceptable Answer Additional Guidance An answer that makes reference to two of the following points: no lid is used (1) SHC of solution may not be 4.18 (1) energy absorbed by zinc / energy absorbed by thermometer / polystyrene cup (1) mass of solution is greater than 25 grams (1) Mark 1 Mark If answer in (c) is less negative than -217, points one and three are valid, and for point two candidates must state less than 4.18 for SHC If answer in (c) is more negative than -217, only point two can be awarded for candidates stating SHC is greater than 4.18 Do not award marks for just ‘heat loss to surroundings’ 2 Acceptable Answer Additional Guidance Mark An explanation that makes reference to the following points: ∆T would be less, so ∆rH / enthalpy change calculated would be less negative (1) because heat energy is transferred to greater volume of water than expected volume (1) 2 (Total for question 6 = 15 marks) 17 CHERRY HILL TUITION EDEXCEL CHEMISTRY A2 PAPER 32 MARK SCHEME Question Number 7 (a) Question Number 7 (b) (i) Question Number 7 (b) (ii) Acceptable Answer Mark +5 1 Acceptable Answer Additional Guidance choice of suitable reducing agent Mark From Data Booklet of the standard electrode potentials, the right hand substance in numbers 1624 Acceptable Answer 1 Additional Guidance Mark An answer that makes reference to the following point: Question Number 7 (b) (iii) Additional Guidance Allow reaction may be too slow may be kinetically hindered or activation energy may be too high 1 Acceptable Answer Additional Guidance Mark An explanation that makes reference to the following points: (yellow to) green then blue (1) when the blue colour initially forms, it mixes with the yellow unreacted VO2+ (to turn green) (1) Ignore colours caused by contamination with reducing agent chosen 2 18 CHERRY HILL TUITION EDEXCEL CHEMISTRY A2 PAPER 32 MARK SCHEME Question Number 7 (b) (iv) Acceptable Answer justification of choice correct equation for reaction Acceptable Answer SO2 + ½O2 → SO3 Mark Eo value is between +0.34 V and −0.26 V An explanation that makes reference to the following point: Question Number 7 (c) (i) Additional Guidance (1) (1) Allow by comparison of electrode potentials / calculation of Ecell / use of anti-clockwise rule S2O32− + VO2+ + 2H+ → V3+ + H2O + ½S4O62− or multiples 2 Additional Guidance Mark Allow multiples Ignore state symbols 1 19 CHERRY HILL TUITION EDEXCEL CHEMISTRY A2 PAPER 32 MARK SCHEME Question Number *7 (c) (ii) Acceptable Answer Additional Guidance This question assesses a student’s ability to show a coherent and logically structured answer with linkages and fully-sustained reasoning. Marks are awarded for indicative content and for how the answer is structured and shows lines of reasoning. The following table shows how the marks should be awarded for indicative content. Number of Number of marks indicative marking awarded for indicative points seen in marking points answer 6 4 5–4 3 3–2 2 1 1 0 0 The following table shows how the marks should be awarded for structure and lines of reasoning. Mark Guidance on how the mark scheme should be applied: The mark for indicative content should be added to the mark for lines of reasoning. For example, an answer with five indicative marking points which is partially structured with some linkages and lines of reasoning scores 4 marks (3 marks for indicative content and 1 mark for partial structure and some linkages and lines of reasoning). If there are no linkages between points, the same five indicative marking points would yield an overall score of 3 marks (3 marks for indicative content and no marks for linkages). Number of marks awarded for structure of answer and sustained line of reasoning Answer shows a coherent and logical structure with linkages and fully sustained lines of reasoning demonstrated throughout Answer is partially structured with some linkages and lines of reasoning Answer has no linkages between points and is unstructured 2 1 0 20 CHERRY HILL TUITION EDEXCEL CHEMISTRY A2 PAPER 32 MARK SCHEME Indicative Content: V2O5 acts as a heterogeneous catalyst SO2 is adsorbed onto surface and reacts with the V2O5 SO3 forms and is only weakly bonded to surface the SO3 desorbs from the surface oxygen reacts with the VO2, regenerating the V2O5 catalyst reaction follows different mechanism with lower activation energy Ignore comments related to collision theory 6 (Total for Question 7 = 14 marks) 21 CHERRY HILL TUITION EDEXCEL CHEMISTRY A2 PAPER 32 MARK SCHEME Question Number 8(a) Acceptable Answer Additional Guidance reagent for step 1 (1) KCN and HCN or KCN and H+ or HCN product of step 1 (1) Allow structural or displayed formulae reagent for step 2 (1) Allow name or formula of any mineral acid Mark 3 Question Number 8(b) Acceptable Answer Additional Guidance Mark (1) esterification (1) 2 22 CHERRY HILL TUITION EDEXCEL CHEMISTRY A2 PAPER 32 MARK SCHEME Question Number 8(c) Acceptable Answer Additional Guidance NO2+ ion (1) Ignore equation to produce electrophile curly arrow from ring to electrophile (1) To any part of the electrophile including the plus sign formula of intermediate (1) curly arrow from CH bond to ring and formation of H+ (1) Mark The horseshoe must cover at least three carbon atoms, opening towards the carbon atom approached by the electrophile and at least part of the plus charge within the horseshoe 4 (Total for Question 8 = 9 marks) 23 CHERRY HILL TUITION EDEXCEL CHEMISTRY A2 PAPER 32 MARK SCHEME Question Number 9(a) Acceptable Answer Additional Guidance Mark For Mg allow 0 or 8 electrons in outermost shell Ignore inner shell electrons 2 Question Number 9(b)(i) Question Number 9 (b) (ii) Acceptable Answer Additional Guidance amount of NaOH (1) Example of calculation 11.7/1000 x 0.100 = 0.00117 / 1.17 x 10−3 [NaOH] (1) 0.00117/(25/1000) = 0.0468 mol dm−3 [NaF]eq (1) 0.250 – 0.0468 = 0.2032 mol dm−3 Kc expression (1) Kc = [NaOH]2 / [NaF]2 Value of Kc (1) 0.0530 (no units) Acceptable Answer Mark 5 Additional Guidance Mark An answer that makes reference to the following point: No, as temperature is likely to be different on different days and this affects value of Kc Allow ‘yes, but only if the temperature is the same’ 1 (Total for Question 9 = 8 marks) 24 CHERRY HILL TUITION EDEXCEL CHEMISTRY A2 PAPER 32 MARK SCHEME Question Number 10(a)(i) Question Number 10(a)(ii) Question Number 10(a)(iii) Acceptable Answer Additional Guidance orange to colourless Mark Allow brown / yellow to colourless 1 Acceptable Answer Additional Guidance Mark A explanation that makes reference to the following points: becomes polar / forms temporary dipole (1) as electron density in C=C bond repels bond pair (of electrons in bromine) (1) Polar bromine can be shown by using a diagram Acceptable Answer e.g. 2 Additional Guidance addition (1) structure (1) Mark Example of structure: 2 25 CHERRY HILL TUITION EDEXCEL CHEMISTRY A2 PAPER 32 MARK SCHEME Question Number 10(a)(iv) Acceptable Answer Additional Guidance Mark Ignore addition of square brackets and n 1 26 CHERRY HILL TUITION EDEXCEL CHEMISTRY A2 PAPER 32 MARK SCHEME Question Number 10(b) Acceptable Answer Raw materials (1) wood is renewable and polystyrene uses slightly more petroleum fractions Energy use paper cup uses nearly 4x as much energy (1) Water use paper cup uses nearly 50x as much water (1) Air emissions paper cup produces chlorine and more sulfur dioxide both of which are toxic / acidic and polystyrene cup produces a lot of hydrocarbons (1) Justification Selection of either cup with two valid reasons (2) Additional Guidance Mark For example: polystyrene is more sustainable, as although it uses up non-renewable raw materials, its production requires much less energy which is likely to save on fossil fuel use or paper is more sustainable, as no hydrocarbons are emitted into the atmosphere and the raw materials are renewable and use less petroleum fractions 6 (Total for Question 10 = 12 marks) 27
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