Version: 10/08/2012

General Certificate of Secondary
Education

Additional Science 4408 /
Chemistry 4402

CH2HP

Unit Chemistry 2

Mark Scheme
2012 examination – June series

Mark schemes are prepared by the Principal Examiner and considered, together with the relevant questions, by a panel of subject teachers. This mark scheme includes any amendments made at the standardisation meeting attended by all examiners and is the scheme which was used by them in this examination. The standardisation meeting ensures that the mark scheme covers the students’ responses to questions and that every examiner understands and applies it in the same correct way. As preparation for the standardisation meeting each examiner analyses a number of students’ scripts: alternative answers not already covered by the mark scheme are discussed at the meeting and legislated for. If, after this meeting, examiners encounter unusual answers which have not been discussed at the meeting they are required to refer these to the Principal 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 to download from the AQA Website: www.aqa.org.uk
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Additional Science / Chemistry – AQA GCSE Mark Scheme 2012 June series

MARK SCHEME
Information to 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 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.
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 confuse the main part of the mark scheme yet may be helpful in ensuring that marking is straightforward and consistent.
2.

Emboldening
2.1

2.2

A bold and is used to indicate that both parts of the answer are required to award the mark.

2.3

3.

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 lines is a potential mark.

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.) 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 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 (indicated as * in example 1) are not penalised.

3

Additional Science / Chemistry – AQA GCSE Mark Scheme 2012 June series

Example 1: What is the pH of an acidic solution? (1 mark)
Student

Response

1
2
3
4

4,8 green, 5 red*, 5 red*, 8

Marks awarded 0
0
1
0

Example 2: Name two planets in the solar system. (2 marks)
Student
1
2

3.2

Response
Neptune, Mars, Moon
Neptune, Sun, Mars,
Moon

Marks awarded
1
0

Use of chemical symbols / formulae
If a student writes a chemical symbol / formula instead of a required chemical name, full credit can be given if the symbol / formula is correct and if, in the context of the question, such action is appropriate.

3.3

Marking procedure for calculations
Full marks can be given for a correct numerical answer, as shown in the column
‘answers’, without any working shown.
However if the answer is incorrect, mark(s) can be gained by correct substitution / working and this is shown in the ‘extra information’ column;

3.4

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.

3.5

Errors carried forward
Any error in the answers to a structured question should be penalised once only.
Papers should be constructed in such a way that the number of times errors can be carried forward are kept to a minimum. Allowances for errors carried forward are most likely to be restricted to calculation questions and should be shown by the abbreviation e.c.f. in the marking scheme.

3.6

Phonetic spelling
The phonetic spelling of correct scientific terminology should be credited unless there is a possible confusion with another technical term.

3.7

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. 4

Additional Science / Chemistry – AQA GCSE Mark Scheme 2012 June series

Quality of Written Communication and levels marking
In Question 2(a) students are required to produce extended written material in English, and will be assessed on the quality of their written communication as well as the standard of the scientific response.
Students will be required to:
• use good English
• organise information clearly
• use specialist vocabulary where appropriate.
The following general criteria should be used to assign marks to a level:
Level 1: Basic
• Knowledge of basic information
• Simple understanding
• The answer is poorly organised, with almost no specialist terms and their use demonstrating a general lack of understanding of their meaning, little or no detail
• The spelling, punctuation and grammar are very weak.
Level 2: Clear
• Knowledge of accurate information
• Clear understanding
• The answer has some structure and organisation, use of specialist terms has been attempted but not always accurately, some detail is given
• There is reasonable accuracy in spelling, punctuation and grammar, although there may still be some errors.
Level 3: Detailed
• Knowledge of accurate information appropriately contextualised
• Detailed understanding, supported by relevant evidence and examples
• Answer is coherent and in an organised, logical sequence, containing a wide range of appropriate or relevant specialist terms used accurately.
• The answer shows almost faultless spelling, punctuation and grammar.

5

Additional Science / Chemistry – AQA GCSE Mark Scheme 2012 June series

CH2HP
Question 1 question 1(a)(i)

answers prevent evaporation of solvent

extra information allow prevent loss of solvent

mark
1

allow to support the
(chromatography) paper
1(a)(ii)

ink dissolves in the solvent

1

allow ink would affect the result / mixes with colours

or carbon / graphite does not dissolve in the solvent
1(b)(i)

allow ink ‘runs’ / spreads or pencil does not ‘run’ / spread

accept pencil for carbon / graphite

4

1

1(b)(ii)

no mark for ‘no / don’t know’ ignore numbers any one from:

1

• because not all colours match
• not all colours are safe
• some colours could be unsafe
• some colours travelled higher
(than safe colours)
1(c)(i)

any two from:
•

accurate

•

sensitive or detects very small quantities

2

rapid / quick

•

ignore reliable / precise

accept small sample

Question 1 continues on the next page . . .

6

Additional Science / Chemistry – AQA GCSE Mark Scheme 2012 June series

CH2HP
Question 1 cont’d….. question answers

1(c)(ii)

separates

1(c)(iii)

identifies solvents / compounds / substances extra information

mark
1

accept (relative) molecular mass

1

accept formula mass accept Mr accept relative mass accept molecular ion peak
Total

8

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Additional Science / Chemistry – AQA GCSE Mark Scheme 2012 June series

CH2HP
Question 2 question 2(a)

0 marks
No
relevant content. answers

extra information

Marks awarded for this answer will be determined by the Quality of
Written Communication (QWC) as well as the standard of the scientific response. Examiners should also refer to the information on page 2, and apply a ‘best-fit’ approach to the marking.
Level 1 (1-2 marks)
There is a simple description of a laboratory procedure for obtaining potassium chloride.

mark
6

Level 2 (3-4 marks)

Level 3 (5-6 marks)

There is a clear description of a laboratory procedure for obtaining potassium chloride from potassium hydroxide solution and hydrochloric acid that does not necessarily allow the procedure to be completed successfully by another person.

There is a detailed description of a laboratory procedure for obtaining potassium chloride from potassium hydroxide solution and hydrochloric acid that can be followed by another person.

The answer must include the use of an indicator / pH meter or a method of obtaining crystals.

The answer must include the use an indicator / pH meter and a method of obtaining crystals

examples of the chemistry points made in the response:
•
•
•
•
•
•
•
•
•
•
•

One reagent in beaker (or similar)
Add (any named) indicator
Add other reagent
Swirl or mix
Add dropwise near end point
Stop addition at change of indicator colour
Note volume of reagent added
Repeat without indicator, adding same volume of reagent or remove indicator using charcoal Pour solution into basin / dish
Heat (using Bunsen burner)
Leave to crystallise / leave for water to evaporate / boil off water

Accept any answers based on titration
Question 2 continues on the next page . . .

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Additional Science / Chemistry – AQA GCSE Mark Scheme 2012 June series

CH2HP
Question 2 cont’d… question 2(b)

answers nitric (acid)

extra information allow HNO3

mark
1

ignore incorrect formula
2(c)(i)

because it is a fertiliser / helps plants grow

allow plant food

1

do not accept pesticide / herbicide / neutralising soil
2(c)(ii)

tick by: ‘Should farmers stop using ammonium nitrate on their land?’ 1

any two from:

2

• cannot be done by experiment

accept difficult to get / not enough evidence • based on opinion / view

allow must be done by survey

• ethical or economic issue if top box ticked allow 1 mark for drinking water varies from place to place
Total

11

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Additional Science / Chemistry – AQA GCSE Mark Scheme 2012 June series

CH2HP
Question 3 question 3(a)

answers

extra information

gives out energy or heat

3(b)(i)

Mark
1

accept qualified answers in terms of volume of gas related to time fast initially

1

slows down

1

reaction stops
3(b)(ii)

21

3(b)(iii)

84

accept reaction is now very slow

1
1

correct answer with or without working = 2 marks

2

allow ecf from 3(b)(ii) correctly calculated for 2 marks allow evidence of 21/25 or 3(b)(ii)/25 for 1 mark
3(c)

because they / particles have more energy / move faster

ignore particles move more / vibrate 1

(and so) particles collide more often / more frequently or particles more likely to collide

ignore collide faster

1

(and) more of the collisions are successful or particles collide with more energy / harder or more of the particles have the activation energy accept more successful collisions

ignore more collisions

Total

1

10

10

Additional Science / Chemistry – AQA GCSE Mark Scheme 2012 June series

CH2HP
Question 4 question answers

4(a)

118

4(b)

it loses / transfers electrons

extra information

mark
1

it = Au / gold atom

1
1

three electrons sharing / covalency = max 1 mark
4(c)(i)

1

O2
2 CO and 2 CO2

accept correct multiples / fractions throughout 1

or correct balancing of equation from
O
4(c)(ii)

reference to incorrect bonding
= 1 mark max
1

because carbon dioxide is simple molecular / small molecules there are intermolecular forces
(between the molecules)

allow intermolecular bonds

1

1

so a small amount of energy needed (to separate molecules) or (intermolecular forces) are weak Question 4 continues on the next page . . .

11

Additional Science / Chemistry – AQA GCSE Mark Scheme 2012 June series

CH2HP
Question 4 cont’d… question 4(d)

answers

extra information

any three from:

mark
3

• gold is the only catalyst for some reactions
• catalysts are not used up
• improves speed of reaction
• reduces amount of energy or process needs low(er) temperature if no mark awarded, allow catalyst reduce costs (of the process) for
1 mark

• only small quantities (of catalyst) needed
Total

11

12

Additional Science / Chemistry – AQA GCSE Mark Scheme 2012 June series

CH2HP
Question 5 question 5(a)

answers
52.9(411765) / 53

extra information correct answer with or without working = 2 marks

mark
2

if answer incorrect allow 2 x 27= 54 or 27/102 x 100 or 26.5 for 1 mark
5(b)(i)

because it lowers the melting point (of the aluminium oxide)

allow lowers the temperature needed 1

do not accept lowers boiling point so less energy is needed (to melt it) 5(b)(iii)

1

2 O2– on left hand side

accept correct multiples or fractions 1

4e–

5(b)(ii)

accept so that the cell / equipment does not melt

accept –4e– on left hand side

1

on right hand side

because the electrode reacts with oxygen or

1

because the electrode burns to form carbon dioxide or

1

electrode made from carbon / graphite Total

8

13

Additional Science / Chemistry – AQA GCSE Mark Scheme 2012 June series

CH2HP
Question 6 question answers

6(a)

because calcium is +2 and hydroxide is –1 or to make the compound neutral (in terms of charges)

accept to balance the charges

particles of size 1-100 nm

allow clear comparison to ‘normal’ size particles

6(b)

extra information

mark
1

allow calcium needs to lose 2 electrons and hydroxide needs to gain one electron
1

or particles with a few hundred atoms / ions or particles with a high surface area (to volume ratio) or as different properties to
‘normal’ size particles of the same substance 6(c)

1

Mr CaO = 56 and Mr Ca(OH)2= 74
2/56 (x74) or 0.036 (x74) or allow ecf from step 1

1

correct answer with or without working gains 3 marks

1

74/56 (x2) or 1.3(214…) (x2)

2.6(428…) in range 2.6 to 2.96

allow ecf carried through from step 1 ignore final rounding to 3
Total

5

14

Additional Science / Chemistry – AQA GCSE Mark Scheme 2012 June series

CH2HP
Question 7 question 7(a)

answers
Graphite:

extra information

mark

it = graphite
1

because the layers (of carbon atoms) in graphite can move / slide accept Van der Waals’ forces allow no covalent bonds between layers 1

however, in diamond, each carbon atom is (strongly / covalently) bonded to 4 others

allow diamond has three dimensional / tetrahedral structure

1

so no carbon / atoms able to move / slide

allow so no layers to slide or so diamond is rigid

1

because graphite has delocalised electrons / sea of electrons

allow free / mobile / roaming electrons 1

this is because there are only weak intermolecular forces or weak forces between layers
Diamond:

7(b)

1

which can carry charge / current or move through the structure however, diamond has no delocalised electrons

accept however, diamond has all
(outer) electrons used in bonding

Total

1

7

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