but-2-ol should be butan-2-ol
2-hydroxybutane should be butan-2-ol
butane-2-ol should be butan-2-ol
2-butanol should be
... [Show More] butan-2-ol
ethan-1,2-diol should be ethane-1,2-diol
2-methpropan-2-ol should be 2-methylpropan-2-ol
2-methylbutan-3-ol should be 3-methylbutan-2-ol
3-methylpentan should be 3-methylpentane
3-mythylpentane should be 3-methylpentane
3-methypentane should be 3-methylpentane
propanitrile should be propanenitrile
aminethane should be ethylamine (although aminoethane can gain credit)
2-methyl-3-bromobutane should be 2-bromo-3-methylbutane
3-bromo-2-methylbutane should be 2-bromo-3-methylbutane
3-methyl-2-bromobutane should be 2-bromo-3-methylbutane
2-methylbut-3-ene should be 3-methylbut-1-ene
difluorodichloromethane should be dichlorodifluoromethane
3.14 Organic reaction mechanisms
Curly arrows should originate either from a lone pair of electrons or from a bond.
The following representations should not gain credit and will be penalised each time
within a clip.
H3C Br
_
:
H C . Br
H3C . .Br
.. _
OH OH
For example, the following would score zero marks
H
H3C C Br
HO H
When the curly arrow is showing the formation of a bond to an atom, the arrow can go directly to the relevant atom, alongside the relevant atom or more than half-way towards the relevant atom.
In free-radical substitution
• the absence of a radical dot should be penalised once only within a clip.
• the use of half-headed arrows is not required, but the use of double-headed arrows or the incorrect use of half-headed arrows in free-radical mechanisms should be penalised once only within a clip
The correct use of skeletal formulae in mechanisms is acceptable, but where a C-H bond breaks, both the bond and the H must be drawn to gain credit.
3.15 Extended responses
For questions marked using a ‘Levels of Response’ mark scheme:
Level of response mark schemes are broken down into three levels, each of which has a descriptor. Each descriptor contains two statements. The first statement is the Chemistry content statement and the second statement is the communication statement.
Determining a level
Start at the lowest level of the mark scheme and use it as a ladder to see whether the answer meets the Chemistry content descriptor for that level. The descriptor for the level indicates the qualities that might be seen in the student’s answer for that level. If it meets the lowest level, then go to the next one and decide if it meets this level, and so on, until you have a match between the level descriptor and the answer.
When assigning a level you should look at the overall quality of the answer and not look to pick holes in small and specific parts of the answer where the student has not performed quite as well as the rest. If the answer covers different aspects of different levels of the mark scheme you should use a best fit approach for defining the level.
Once the level has been decided, the mark within the level is determined by the communication statement:
• If the answer completely matches the communication descriptor, award the higher mark within the level.
• If the answer does not completely match the communication descriptor, award the lower mark within the level.
The exemplar materials used during standardisation will help you to determine the appropriate level. There will be an exemplar in the standardising materials which will correspond with each level of the mark scheme and for each mark within each level. This answer will have been awarded a mark by the Lead Examiner. You can compare the student’s answer with the exemplar to determine if it is the same standard, better or worse than the example. You can then use this to allocate a mark for the answer based on the Lead Examiner’s mark on the exemplar.
You may well need to read back through the answer as you apply the mark scheme to clarify points and assure yourself that the level and the mark are appropriate.
Indicative content in the mark scheme is provided as a guide for examiners. It is not intended to be exhaustive and you must credit other chemically valid points. Students may not have to cover all of the points mentioned in the indicative content to reach the highest level of the mark scheme. The mark scheme will state how much chemical content is required for the highest level.
An answer which contains nothing of relevance to the question must be awarded no marks.
For other extended response answers:
Where a mark scheme includes linkage words (such as ‘therefore’, ‘so’, ‘because’ etc), these are optional. However, a student’s marks for the question may be limited if they do not demonstrate the ability to construct and develop a sustained line of reasoning which is coherent, relevant, substantiated and logically structured. In particular answers in the form of bullet pointed lists may not be awarded full marks if there is no indication of logical flow between each point or if points are in an illogical order.
The mark schemes for some questions state that the maximum mark available for an extended response answer is limited if the answer is not coherent, relevant, substantiated and logically structured. During the standardisation process, the Lead Examiner will provide marked exemplar material to demonstrate answers which have not met these criteria. You should use these exemplars as a comparison when marking student answers.
Question Marking guidance Additional Comments/Guidelines Mark
01.1
M1
M2
The enthalpy / heat energy change when 1 mol (of a substance / compound / product) is formed from its (constituent) elements
with (all) reactants and products / all substances in standard states M1 energy change is not sufficient – must refer to enthalpy change or heat energy change
M2 or with (all) reactants and products / substances in normal states under standard conditions / 100 kPa and any specified temperature (usually 298 K) 1
1
Ignore reference to 1 atmosphere
If enthalpy of combustion given rather than formation, then mark M1 and M2 independently, and M2 could score.
M1 ∆H = [sum ∆fH products] – [sum ∆fH reactants] –303 scores 3 marks (+303 scores 2 marks)
–909 scores 2 marks (+909 scores 1 mark) ignore units
M2 No ECF from M1 (except +909 or arithmetic error)
M3 ECF from M2, ie M3 3 1
or –114 = [3(–130) – 972] – [3X – 339]
01.2
M2 or 3X = 3(–130) – 972 + 339 + 114
3X = –909
1
M3 X = –303 (kJ mol–1)
1
01.3 M1 provides energy to break (covalent) bond in chlorine / Cl2 or to form chlorine free radicals
M2 CH3CH2CH3 + •Cl •CH2CH2CH3 + HCl
M3 •CH2CH2CH3 + Cl2 ClCH2CH2CH3 + •Cl
M2 and M3:
• must show structure of •CH2CH2CH3 in at least one of the equations to score both marks (dot must be on or around the end CH2 group), but only penalise •C3H7 once across both equations if both equations otherwise correct
• on this occasion, molecular formula of propane can be allowed for M2
• on this occasion, molecular formula of 1-chloropropane can be allowed for M3
• penalise absence of radical dots once
• allow equations in either order 1
1
1
01.4 the ability/power of atom
to attract/withdraw the 2/pair of electrons in a covalent bond allow nucleus in place of atom 1
01.5 M1 nucleophilic substitution
M2 curly arrow from lone pair on N of NH3 to the correct C atom
M3 must show the movement of a pair of electrons from the C−Cl bond to the Cl atom; mark M3 independently provided it is from their original molecule
M4 is for the structure of the alkylammonium ion, which could be a condensed formula; a positive charge must be shown on, or close to, the N atom
M5 is for an arrow from the N−H bond to the N atom
For the mechanism
Penalise M2 if negative charge on ammonia
Penalise M3 for formal charge on C and/or Cl of C–Cl or incorrect partial charges on C–Cl; ignore other partial charges on uncharged atoms
penalise M3 for any additional arrow(s) to/from the Cl to/from anything else
the second molecule of NH3 is not essential for M5, but penalise M5 if used incorrectly (but only penalise once in M2 and M5 for negative charge on ammonia)
SN1 mechanism alternative (loss of Cl first followed by attack by NH3) :
M2 curly arrow from C–Cl bond to the Cl
M3 curly arrow from lone pair of NH3 to correct C on the correct carbocation 1
1
1
1
1
Question Marking guidance Additional Comments/Guidelines Mark
02.1 Idea that it is hard to judge to the nearest 0.01 second or
Idea that it is hard to judge the exact moment (that it becomes too cloudy / the cross disappears) or
the idea of reaction time Ignore ideas relating to accuracy (unless qualified) 1
02.2 0.083(3….) 1
02.3 M1 points plotted correctly (allow ±1/2 small square for each)
M2 suitable best fit curve that misses point at 49°C and passes within one small square of the other five points
If any points plotted incorrectly: best fit line based on their plotted points which may need to be more than one square away from some points
If no value calculated in 2.2, then M1 and M2 based on the other points (except the fifth anomalous point). A straight line may be allowed for M2 for the first four points.
If incorrect value calculated in 2.2: M1 based on all values being plotted correctly; M2 based on suitable best fit line for the plotted points (except the fifth anomalous point).
Penalise M2 if best fit line goes to 0,0.
2
02.4 1
value from their best fit line at 40°C
eg 1 = 29 (s)
0.0345
Ignore units 1
02.5 as it forms a toxic gas or SO2 is toxic/poisonous or
to limit amount of SO2 formed Ignore reference to SO2 being harmful Ignore reference to acid rain / pollutant 1
02.6 reaction would take too long / too slow / take a long time / very slow Ignore reaction may not occur
Allow idea that it makes judging the moment when the cross disappears more difficult 1 [Show Less]