3.13 Organic names
As a general principle, non-IUPAC names or incorrect spelling or incomplete names should not gain credit. Some illustrations are given
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Unnecessary but not wrong numbers will not be penalised such as the number ‘2’ in 2- methylpropane or the number ‘1’ in 2-chlorobutan-1-oic acid.
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 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 Answers Additional comments/Guidelines Mark
M1
M2
M3 tangent drawn to the curve at 0,0
Evidence of value used in calculation leading to initial rate = 5.5
cm3 s−1
If tangent not drawn at 0,0 then allow conseq gradient calculation 1
1
01.1
Note allow 5 – 7
1
NOT cm3 / s
M1 [H2PO2 ] 1/t
– 2 Accept time argument eg if conc doubled time is quartered 1
01.2 Accept suitable words that implies a square or square root relationship
M2 Order = 2 Not simple description of as conc increases time decreases 1
01.3
Either gas syringe or measuring cylinder over water
Tubing shown should not be closed Syringe should have a plunger shown Allow lack of graduations
1
01.4 Falls by a factor of 8
OR Multiplied by 1/8
OR Divided by 8
Allow halved then quartered / Decreases by 23
1
Re-arrangement
M1
[M]2
=
Rate
Inserts correct numbers into their rearranged expression
1
k [L] 1
01.5 M2
M3 [M]2
[M] = = 0.0250
21.3 × 0.0155
√7.57 × 10–2 (=7.57 × 10–2)
= 0.275 mol dm–3 (min 2 sf) Takes square root (allow ecf for square root of their M2)
Common error is to use 0.25 rather than 0.025. This leads to an answer of 0.870. Scores 2
1
Upside-down expression leads to an answer of
3.63. Scores 2
01.6
The sum of powers/indices (to which the concentrations are raised in the rate equation) All the orders added/ sum of the (individual) orders
This can be explained using a general rate equation stated as an example
e.g. Rate = k[A]x[B]y and the overall order is x + y
1
Question Answers Additional comments/Guidelines Mark
02.1 One circled C atom only – The C attached to CH3/C=O/ H and NH 1
02.2 Two ticks only for amine and amide 1
02.3
M1 for choosing the correct bond to hydrolyse M2 and M3 for the correct structures of the products
Allow protonated amino acid for M2
H
H H
C H H H H
H O
C C N C C C H
O H H H H H
+
Allow C6H5NH3 or + outside a square bracket 3
02.4 M1 Enzyme has an active site
M2
The G-Enantiomer / Enzyme has the correct stereo chemistry / stereospecific
Or
The G-Enantiomer / Enzyme has the complementary shape
For M2 allow opposite argument for F-Enantiomer 1
1
Question Answers Additional comments/Guidelines Mark
03.1
M1 Q, R, S, T
M2 (Orange solution) turns green M1 Allow the mark for candidates who correctly name or draw the isomers.
Independent 1
1
03.2 M1 T
M2 Silver mirror As above
Allow grey/black ppt 1
1
03.3 M1 P, Q, R, S
M2 Sweet smelling (liquid)
M3 To react with (remove excess) acid / neutralise As above
Allow easier to identify the smell 1
1
1
03.4 Position
Allow positional
1
03.5
M1 R & S have an O-H alcohols peak at 3230-3550 cm−1
M2 T has C=O peak at 1680-1750 cm−1
M3 R & S (unique) fingerprint region or below 1500 cm−1
M4 Compare to a database / known spectra (and look for an exact match)
Allow value within the range
1
1
1
1
03.6
All have the same Mr Allow
same (molecular) ion M/Z peak same molecular formula 1
Question Answers Additional comments/Guidelines Mark
04.1 M1 (Re)weigh the empty boat
M2 In order to calculate the (exact) mass of salicylic acid added to the reaction mixture 1
1
04.2 10 cm3 measuring cylinder (if volume given – allow between 10 to 50 cm3)
Or a 10 cm3 pipette
Or burette / graduated pipette Or 10 cm3 syringe 1
04.3
Corrosive Allow skin burn / permanent eye damage Ignore irritant / toxic
1
04.4 LHS + (CH3CO)2O RHS + CH3COOH 1
04.5
M1 Amount salicylic acid = 6.01/138 = 4.36×10–2 mol
M2 Mass (CH3CO)2O = 10.5 × 1.08 = 11.34 g
M3 Amount (CH3CO)2O = 11.34/102 = 1.11×10–1 mol
M4 (CH3CO)2O is in excess
M5 Mass aspirin = M1 × 0.841 × 180 = 6.59 g Allow conseq from wrong mole ratio in 04.4
Must show and state that ethanoic anhydride is in excess
For M4/M5 ecf from M1/M3 Allow 2 sf or more. 1
1
1
1
1
04.6
M1 Value lower
M2 Range of values
For M2 allow mpt not sharp or a larger range of melting points 1
1
04.7 M1 (Ethanol is flammable so) use a water bath to heat / do not use a Bunsen burner
M2 Heat to temp below bp (so ethanol does not boil away) Must give practical step, not just state hazard
Allow use min vol solvent 1
1
04.8
To remove any soluble impurities Allow To avoid aspirin dissolving (small amount cold solvent used)
Allow To remove/(wash away) any ethanolic solution on the product.
1
04.9
Pure product will have (larger) crystals / needle-like crystals / lighter in colour Allow whiter, less grey, more crystalline, less powdery, shinier, single colour
Must be tied to pure product
Allow opposite points tied to the crude product
1
Question Answers Additional comments/Guidelines Mark
M1
M2 M3 The (relative) tendency of an atom to attract a pair of electrons/ the electrons/ electron density in a covalent bond
Br is more electronegative than C (or vice versa) So Br is δ- and C is δ+ 1
05.1
1
1
05.2
M4 Penalise loss of H+ using Br- Allow Sn1
4
Allow + outside square brackets
1
05.3
M1
M2 Use: (Hair) conditioner / (Cationic) surfactant / disinfectant Allow fabric softener 1
Question
Answers Additional comments/Guidelines
Mark
Allow electrophilic substitution 1
Allow ethanoic anhydride for 1
M1 Acylation M2 1
06.1 M2 CH3COCl OR Ethanoyl chloride M3 dependent on M2
M3 AlCl3 OR Aluminium chloride (mark could be awarded in space for M2) Allow Dry/anhydrous for M3
Apply list principle to extra incorrect conditions [Show Less]