AS

CHEMISTRY
7404/1
Paper 1 Inorganic and Physical Chemistry
Mark scheme
June 2020
Version: 1.0 Final

*206A7404/1/MS*
 MARK SCHEME – AS CHEMISTRY – 7404/1 – JUNE 2020

Mark schemes are prepared by the Lead Assessment Writer and considered, together with the relevant
questions, by a panel of subject teachers. This mark scheme includes any amendments made at the
standardisation events which all associates participate in and is the scheme which was used by them in
this examination. The standardisation process ensures that the mark scheme covers the students’
responses to questions and that every associate understands and applies it in the same correct way.
As preparation for standardisation each associate analyses a number of students’ scripts. Alternative
answers not already covered by the mark scheme are discussed and legislated for. If, after the
standardisation process, associates encounter unusual answers which have not been raised they are
required to refer these to the Lead Examiner.

It must be stressed that a mark scheme is a working document, in many cases further developed and
expanded on the basis of students’ reactions to a particular paper. Assumptions about future mark
schemes on the basis of one year’s document should be avoided; whilst the guiding principles of
assessment remain constant, details will change, depending on the content of a particular examination
paper.

Further copies of this mark scheme are available from aqa.org.uk

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Copyright © 2020 AQA and its licensors. All rights reserved.

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 MARK SCHEME – AS CHEMISTRY – 7404/1 – JUNE 2020

AS and A-Level Chemistry

Mark Scheme Instructions for Examiners
1. General
The mark scheme for each question shows:
• the marks available for each part of the question
• the total marks available for the question
• the typical answer or answers which are expected
• extra information to help the examiner make his or her judgement and help to delineate what
is acceptable or not worthy of credit or, in discursive answers, to give an overview of the area
in which a mark or marks may be awarded.
The extra information in the ‘Comments’ column is aligned to the appropriate answer in the left-
hand part of the mark scheme and should only be applied to that item in the mark scheme.
You should mark according to the contents of the mark scheme. If you are in any doubt about
applying the mark scheme to a particular response, consult your Team Leader.
At the beginning of a part of a question a reminder may be given, for example: where
consequential marking needs to be considered in a calculation; or the answer may be on the
diagram or at a different place on the script.
In general the right-hand side of the mark scheme is there to provide those extra details which
might confuse the main part of the mark scheme yet may be helpful in ensuring that marking is
straightforward and consistent.
The use of M1, M2, M3 etc in the right-hand column refers to the marking points in the order in
which they appear in the mark scheme. So, M1 refers to the first marking point, M2 the second
marking point etc.

2. Emboldening
2.1 In a list of acceptable answers where more than one mark is available ‘any two from’ is
used, with the number of marks emboldened. Each of the following bullet points is a
potential mark.
2.2 A bold and is used to indicate that both parts of the answer are required to award the
mark.
2.3 Alternative answers acceptable for a mark are indicated by the use of OR. Different terms
in the mark scheme are shown by a / ; eg allow smooth / free movement.

3. Marking points
3.1 Marking of lists
This applies to questions requiring a set number of responses, but for which students
have provided extra responses. The general ‘List’ principle to be followed in such a
situation is that ‘right + wrong = wrong’.
Each error / contradiction negates each correct response. So, if the number of error /
contradictions equals or exceeds the number of marks available for the question, no
marks can be awarded.
However, responses considered to be neutral (often prefaced by ‘Ignore’ in the mark
scheme) are not penalised.

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For example, in a question requiring 2 answers for 2 marks:

Incorrect
Correct answers (ie
Mark (2) Comment
answers incorrect rather
than neutral)
1 0 1
They have not exceeded the maximum
1 1 1
number of responses so there is no penalty.
They have exceeded the maximum number
1 2 0 of responses so the extra incorrect
response cancels the correct one.
2 0 2
2 1 1
2 2 0
3 0 2 The maximum mark is 2
The incorrect response cancels out one of
3 1 1 the two correct responses that gained
credit.
Two incorrect responses cancel out the two
3 2 0
marks gained.
3 3 0

3.2 Marking procedure for calculations

Full marks should be awarded for a correct numerical answer, without any working
shown, unless the question states ‘Show your working’ or ‘justify your answer’. In this
case, the mark scheme will clearly indicate what is required to gain full credit.
If an answer to a calculation is incorrect and working is shown, process mark(s) can
usually be gained by correct substitution / working and this is shown in the ‘Comments’
column or by each stage of a longer calculation.

3.3 Errors carried forward, consequential marking and arithmetic errors

Allowances for errors carried forward are most likely to be restricted to calculation
questions and should be shown by the abbreviation ECF or consequential in the marking
scheme.
An arithmetic error should be penalised for one mark only unless otherwise amplified in
the marking scheme. Arithmetic errors may arise from a slip in a calculation or from an
incorrect transfer of a numerical value from data given in a question.

3.4 Equations
In questions requiring students to write equations, state symbols are generally ignored
unless otherwise stated in the ‘Comments’ column.

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Examiners should also credit correct equations using multiples and fractions unless
otherwise stated in the ‘Comments’ column.
3.5 Oxidation states
In general, the sign for an oxidation state will be assumed to be positive unless
specifically shown to be negative.

3.6 Interpretation of ‘it’

Answers using the word ‘it’ should be given credit only if it is clear that the ‘it’ refers to the
correct subject.

3.7 Phonetic spelling

The phonetic spelling of correct scientific terminology should be credited unless there is a
possible confusion with another technical term or if the question requires correct IUPAC
nomenclature.

3.8 Brackets
(…..) are used to indicate information which is not essential for the mark to be awarded
but is included to help the examiner identify the sense of the answer required.

3.9 Ignore / Insufficient / Do not allow

Ignore or insufficient is used when the information given is irrelevant to the question or not
enough to gain the marking point. Any further correct amplification could gain the marking
point.
Do not allow means that this is a wrong answer which, even if the correct answer is
given, will still mean that the mark is not awarded.

3.10 Marking crossed out work

Crossed out work that has not been replaced should be marked as if it were not crossed
out, if possible. Where crossed out work has been replaced, the replacement work and
not the crossed out work should be marked.

3.11 Reagents
The command word “Identify”, allows the student to choose to use either the name or the
formula of a reagent in their answer. In some circumstances, the list principle may apply
when both the name and the formula are used. Specific details will be given in mark
schemes.

The guiding principle is that a reagent is a chemical which can be taken out of a bottle or
container. Failure to identify complete reagents will be penalised, but follow-on marks
(eg for a subsequent equation or observation) can be scored from an incorrect attempt
(possibly an incomplete reagent) at the correct reagent. Specific details will be given in
mark schemes.

For example, no credit would be given for

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• the cyanide ion or CN– when the reagent should be potassium cyanide or KCN;
• the hydroxide ion or OH– when the reagent should be sodium hydroxide or NaOH;
• the Ag(NH3)2+ ion when the reagent should be Tollens’ reagent (or ammoniacal silver
nitrate). In this example, no credit is given for the ion, but credit could be given for a
correct observation following on from the use of the ion. Specific details will be given in
mark schemes.

In the event that a student provides, for example, both KCN and cyanide ion, it would be
usual to ignore the reference to the cyanide ion (because this is not contradictory) and
credit the KCN. Specific details will be given in mark schemes.

3.12 Organic structures

Where students are asked to draw organic structures, unless a specific type is required in
the question and stated in the mark scheme, these may be given as displayed, structural
or skeletal formulas or a combination of all three as long as the result is unambiguous.
In general
• Displayed formulae must show all of the bonds and all of the atoms in the molecule, but
need not show correct bond angles.
• Skeletal formulae must show carbon atoms by an angle or suitable intersection in the
skeleton chain. Functional groups must be shown and it is essential that all atoms
other than C atoms are shown in these (except H atoms in the functional groups of
aldehydes, secondary amines and N-substituted amides which do not need to be
shown).
• Structures must not be ambiguous, eg 1-bromopropane should be shown as
CH3CH2CH2Br and not as the molecular formula C3H7Br which could also represent the
isomeric 2-bromopropane.
• Bonds should be drawn correctly between the relevant atoms. This principle applies in
all cases where the attached functional group contains a carbon atom, eg nitrile,
carboxylic acid, aldehyde and acid chloride. The carbon-carbon bond should be clearly
shown. Wrongly bonded atoms will be penalised on every occasion. (see the
examples below)
• The same principle should also be applied to the structure of alcohols. For example, if
students show the alcohol functional group as C ─ HO, they should be penalised on
every occasion.
• Latitude should be given to the representation of C ─ C bonds in alkyl groups, given
that CH3─ is considered to be interchangeable with H3C─ even though the latter
would be preferred.
• Similar latitude should be given to the representation of amines where NH2─ C will be
allowed, although H2N─ C would be preferred.
• Poor presentation of vertical C ─ CH3 bonds or vertical C ─ NH2 bonds should not be
penalised. For other functional groups, such as ─ OH and ─ CN, the limit of tolerance
is the half-way position between the vertical bond and the relevant atoms in the
attached group.

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By way of illustration, the following would apply.

CH3 C C C OH C C

CH3 CH3CH2 OH

allowed allowed not allowed not allowed not allowed

NH2 NO2

NH2 C C

NH2
NH2

allowed allowed allowed allowed not allowed

CN C C COOH C C C

CN COOH COOH

not allowed not allowed not allowed not allowed not allowed

CHO C C C COCl C C

CHO CHO COCl

not allowed not allowed not allowed not allowed not allowed

• Representation of CH2 by C−H2 will be penalised

• Some examples are given here of structures for specific compounds that should not
gain credit (but, exceptions may be made in the context of balancing equations)

CH3COH for ethanal

CH3CH2HO for ethanol

OHCH2CH3 for ethanol
C2H6O for ethanol

CH2CH2 for ethene

CH2.CH2 for ethene
CH2:CH2 for ethene

• Each of the following should gain credit as alternatives to correct representations of

the structures.

CH2 = CH2 for ethene, H2C=CH2

CH3CHOHCH3 for propan-2-ol, CH3CH(OH)CH3

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• In most cases, the use of “sticks” to represent C ─ H bonds in a structure should not be
penalised. The exceptions to this when “sticks” will be penalised include
• structures in mechanisms where the C ─ H bond is essential (eg elimination
reactions in halogenoalkanes and alcohols)
• when a displayed formula is required
• when a skeletal structure is required or has been drawn by the candidate

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 here.
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

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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.

. . Br
H3C Br H3C .. Br H3C

_ .._
: OH OH
For example, the following would score zero marks

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.

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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.

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Question Marking guidance Additional Comments/Guidelines Mark

Aluminium / Al Allow M2/M3 if a Group 3 element is given 1

(Outer) electron in (3)p orbital / sub-shell (level) Not energy level 1

(3p) higher in energy / slightly more shielded (than 3s) / slightly 1

further away (than 3s)
OR
01.1
or
1
Sulfur / S Allow M2/M3 if a Group 6 element is given 1
(Outer) electrons in (3)p orbital begin to pair Do not allow just p4 vs p3 1
Repel

Na2+(g) → Na3+(g) + e− State symbols essential.

01.2 1
Allow
Na2+(g) + e– → Na3+(g) + 2 e−

M1 Phosphorus / P Mark independently

M2 large jump in ionisation energy for the 6th ionisation energy Large jump after the 5 e– is removed / when the 6th
01.3 e– is removed 3
M3 This is when the electron is being removed from the 2nd (principle)
energy level / from a lower energy level / from a lower shell / from 2p /
from an energy level that is closer to the nucleus

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Question Marking guidance Additional Comments/Guidelines Mark

M1 Volume of H2SO4 = (19.60 + 19.55) / 2 =

M1 = calculation of mean titre
= (19.575 cm3 / 19.58 cm3) M2 = M1 x 10–3 x 0.150

M2 Moles of H2SO4 = concentration x volume M3 = M2 x 2

= 0.150 x (19.575 / 1000) M4 = M3 x 8

M5 = 1.879g
(= 2.936 x 10–3 mol)
02.1 5
M3 Moles of NaOH in 25 cm3 = 2.936 x 10–3 x 2 = (5.87 x 10–3 mol)

M4 Moles of NaOH in original 200 cm3 sample = 5.87 x 10–3 x 8 Allow correct alternative approaches

(= 0.04698 mol)

M5 Mass of NaOH = Mr x moles = 40.0 x 0.04698

= 1.88 g (1.9 g)

Additional drops of solution could have entered the burette from the Must imply that solution from funnel drips into
02.2 1
funnel, (making the value on the burette lower). burette

Less chance of splashing/losing any solution using a conical flask Allow easier to swirl
02.3 1
(when swirling)

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Question Marking guidance Additional Comments/Guidelines Mark

The average mass of an atom of an element (Weighted) average mass of all isotopes of an
1
element
03.1
1
Compared to 1/12th the mass of an atom of carbon-12

R.A.M. = (82 x 6) + (83 x 1) + (84 x 28) + (86 x 8) M1 for working 1

43
03.2
= 3615 / 43 M2 for answer to 1 decimal place
= 84.1 36.2 scores 1/2 1

M1 m = (84/1000)/6.02 x 1023 Alternative method

(= 1.395 x 10-25 kg) M1: m = (84/1000)/6.02 x 1023
(= 1.395 x 10-25 kg)
M2 v2 = 2ke/m
= 2 x (4.83 × 10−16) / (1.395 x 10-25) M2: d2 = 2 ke t2/m

M3 v = √(6924731183) M3:
03.3 = 83214.97 d2 = 2 x (4.83 × 10−16) x (1.73 x 10–5)2 / 1.395 x 10-25 4
d2 = 2.07
M4 d =vxt
= 83214.97 x 1.72 × 10−5 M4 = 1.44 (m)
= 1.43 (m)
Allow answers in range 1.43 – 1.44 m

If m not converted to kg, then d = 0.045m for max 3

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Question Marking guidance Additional Comments/Guidelines Mark

04.1 Heat energy change at constant pressure 1

This question is marked using levels of response. Indicative Chemistry

Level 3:
Stage 1: Apparatus
All stages are covered and the explanation of each stage is
1a. Use a burette/pipette (instead of a measuring
generally correct and virtually complete.
cylinder)
Answer is well structured with no repetition or irrelevant 5-6 1b. Use a polystyrene cup (instead of a beaker) /
points. insulate beaker
Accurate and clear expression of ideas with no errors in use 1c. Reweigh the watchglass after adding the solid
of technical terms. 1d: Use powdered solid
Level 2:
All stages are covered but the explanation of each stage may Stage 2: Temperature Measurements
be incomplete or may contain inaccuracies OR two stages are 2a. Measure and record the initial temperature of
covered and the explanations are generally correct and the solution for a few minutes before addition
virtually complete. 2b. Measure and record the temperature after the
3-4
addition at regular intervals (eg each minute) for 8+
04.2 Answer shows some attempt at structure minutes/until a trend is observed 6
Ideas are expressed with reasonable clarity with, perhaps,
some repetition or some irrelevant points. Stage 3: Temperature Determination
Some minor errors in use of technical terms. 3a. Plot a graph of temperature against time
Level 1: 3b. Extrapolate to the point of addition
Two stages are covered but the explanation of each stage 3c. Determine ΔT at the point of addition
may be incomplete or may contain inaccuracies, OR only one
stage is covered but the explanation is generally correct and
virtually complete. 1-2
Answer includes isolated statements but these are not
presented in a logical order or show some confusion.
Answer may contain valid points which are not clearly linked
to an argument structure. Errors in the use of technical terms.
Level 0
0
Insufficient correct chemistry to gain a mark.

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n(HCl) or n(NaOH) = 50 x 0.500 / 1000 = 0.025 moles

1
q = –ΔH x n = 57.1 x 0.025 = 1.4275 kJ M2 = 57.1 × M1
1
ΔT = q/mc
04.3 1
ΔT = (1.4275 x 1000) / (100 x 4.18) = 3.4(2) °C M4 = (M2 × 1000) / (100 × 4.18)
1
Final Temperature = 18.5 + 3.4 = 21.9 °C M5 = M4 + 18.5 (but final temperature must be 1
higher than 18.5 °C)

04.4 Increase the concentration of the solutions 1

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Question Marking guidance Additional Comments/Guidelines Mark

Mg2+ has a higher charge than Na+ / Mg2+ ions are smaller / Mg2+ has Allow
a greater charge density / Mg atoms smaller than Na atoms / Mg has Mg has a higher nuclear charge 1
more delocalised electrons than Na
05.1
Stronger attraction to delocalised sea of electrons / stronger metallic 1
bonding Not attraction for outer electrons

2Mg + TiCl4 → 2MgCl2 + Ti Allow multiples 1

05.2 Mg changes oxidation state from 0 to +2 so electrons are lost / Ti Allow

changes oxidation state from +4 to 0 , so gains electrons Oxidation state of Mg increases so it is a reducing 1
agent

Observation with MgCl2: (slight) white ppt

1
Observation with BaCl2: no (visible) change / colourless solution / no Do not allow nothing / no observation
05.3
reaction 1

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Question Marking guidance Additional Comments/Guidelines Mark

Shapes: Must show lp on NCl3 1

1
+
Cl Must have some indication that shape is 3D
xx +
N N
Cl Cl Cl Cl
Cl Cl
06

Name of shape of NCl3 = Pyramidal Allow tetrahedral 1

Bond Angle = 109.5° Allow 109 – 109.5° 1

(4 bp and 0 lp) electron pairs repel equally / electron pairs repel to be Do not allow atoms repel equally 1
as far apart as possible Allow bonds repel equally

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Question Marking guidance Additional Comments/Guidelines Mark

Reason: sterilise water / disinfect water / kill bacteria / kill

microorganisms / kill microbes 1

Explanation: health benefit outweighs risk / only used in small

07.1 quantities/low concentrations 1

Equation:
Cl2 + H2O ⇌ HCl + HClO 1
2 Cl2 + 2 H2O → 4 HCl + O2

2I– → I2 + 2e 1

H2SO4 + 6H+ + 6e → S + 4H2O Allow S8 1

07.2
6H+ + 6I- + H2SO4 → 3I2 + S + 4H2O Allow correct equations using 8H+ + SO42– 1

SO2 or H2S Mark independently 1

To ensure that all the halide ions (chloride and iodide) are removed Must refer either to both halide ions, or to all halide
07.3 from the solution / to ensure that all the halide ions precipitate out of ions. 1
solution

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Question Marking guidance Additional Comments/Guidelines Mark

n(AgI) = 0.315/234.8 = 1.34 x 10–3 moles

07.4
1

n(NaI) = 1.34 x 10–3 Ans (07.4) x 149.9

07.5 1
mass of NaI = 1.34 x 10–3 x 149.9 = 0.201g

mass of NaCl = 600 – 201 = 399mg 600 – (Ans 07.5 x 1000) 1

%NaCl = 399/600 x 100 = 66.5% M1/600 x 100 1

(66.5 – 68.3)
07.6 OR

(Ans 07.5 x 1000) / 600 x 100

100 – M1

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Question Marking guidance Additional Comments/Guidelines Mark

M1 n = pV / RT M1 for rearrangement
M2 for three unit conversions
M2 n = 100000 x ( 178/1000000) M3 for calculating the amount in moles of A
8.31 x (273 + 120) M4: 0.460 / M3 given to 3sf

08.1 M3 n = 5.45 × 10−3 mol 4

Mr = or 0.460 / 5.45 × 10−3

M4 Mr = 84.4 Answer must be to 3 sig.fig.

Calculated Mr value would be greater than actual Mr = mass / moles so dividing by too small a value
of moles gives a larger Mr than expected.
1

08.2
A lower volume would have been recorded / mass evaporated less
1
than mass of liquid / lower moles calculated / mass recorded higher
than mass of gas / mass recorded would be too high
M2 dependent on correct M1

% uncertainty = ( uncertainty / mass added) x 100

1
08.3 = ((2 x 0.001) / 0.460} x 100
= 0.435%

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Question Marking Guidance Mark Comments

4
9 D 1 Li

10 C 1 CH3Cl

11 B 1 NH3

12 D 1 Li(s) + ½ F2(g) → LiF(s)

13 A 1 1

14 B 1 1s22s22p4

15 C 1 Be2+ Li+ F– O2–

16 D 1 NH4Cl

17 B 1 boiling point

18 C 1 Silicon

19 A 1 The concentrations of the reactants and products are equal.

20 B 1 –278

21 A 1 Cl2O

22 D 1 I2(aq) + 2 KBr(aq) → Br2(aq) + 2KI(aq)

23 D 1 Cl2O

21