aqa-8402-1-w-ms-jan14

AQA Level 1/2 Certificate Chemistry Paper 1 (8402/1) Mark scheme 8402 January 2014 Version/Stage: Final

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 Assessment Writer. 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 years 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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MARK SCHEME AQA Certificate in Chemistry Paper 1 8402/1 January 2014

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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 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 candidates 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.

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

Candidate Response Marks awarded

1 green, 5 0 2 red*, 5 1 3 red*, 8 0


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

Candidate Response Marks awarded 1 Neptune, Mars, Moon 1 2 Neptune, Sun, Mars,

Moon 0

3.2 Use of chemical symbols / formulae

If a candidate 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, 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 or by each stage of a longer calculation.

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.

3.8 Ignore / Insufficient / Do not allow Ignore of 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.


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4. Quality of Communication and levels marking In Question 5(c) candidates 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. Candidates 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.


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Question Answers Extra information Mark AO/spec ref

1(a)(i)

Neutron (top label)

Electron (bottom label)

1

1

AO1

1.2c

1(a)(ii)

13 1 AO1

1.2i

1(a)(iii)

electrons 1 AO1

1.2e

1(b)(i)

compound

hydrogen

bond

1

1

1

2AO1/1AO2

1.2b, 1.3a, 8.2a, 8.2b

1(b)(ii)

C4H10 1 AO2

8.2b

Total 8


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2(a)(i)

iron

carbon dioxide

either order 1

1

AO2

1.3f, 6.2b

2(a)(ii)

reduced 1 AO1

6.2b

2(b)(i)

each correct line gains 1 mark

extra lines from statement negate the mark

max. 2

AO1

1.2a, 14.2a

2(b)(ii)

the layers / rows are distorted / disrupted or it doesnt occur in layers or the atoms are different so cannot slide over one another or slide less easily

1

1

AO1/AO2

6.3e

Total 7


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3(a)(i)

Solids 1 AO1

3.2b

3(a)(ii)

Chlorine 1 AO1

3.2b

3(a)(iii)

improves dental health or reduces tooth decay

1 AO1

3.2d

3(b)

put a sample of the filtered water in an evaporating basin or leave to evaporate

there will be crystals of salt left

accept any description of evaporation (using a Bunsen or leaving on the windowsill)

1

1

AO1/AO2

3.2a, 3.2c

3(c)(i)

Test flame test Result yellow / orange / persistent orange flame

1

1

AO1

14.1e

3(c)(ii)

sodium and / or chloride ions are bigger than water (molecules) or ions are charged or molecules are not charged

do not accept sodium chloride molecules as ions is given in the question

1 AO3

3.2a, 14.2a

Total 8


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4(a)

colourless ignore clear 1 AO1

9.1d

4(b)(i)

decomposition 1 AO1

9.1a

4(b)(ii)

C8H18 1 AO2

1.3f, 9.1b

4(c)(i)

two single trailing bonds extending from the carbons (through the brackets) 1 mark five single bonds (1 CC bond and 4 CH bonds) 1 mark

2 AO1

9.2a

4(c)(ii)

any two from:

(polymers made from) cornstarch are biodegradable

less space needed in landfill sites

polymers from cornstarch come from a renewable source.

allow converse for poly(ethene)

2 AO1/AO3

9.2e, 9.2f

Total 7


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5(a)(i)

covalent 1 AO1

2.1g, 2.1h

5(a)(ii)

increases the rate of reaction 1 AO1

7g

5(b)(i)

the reaction is reversible 1 AO1

1.3i, 12b

5(b)(ii)

at lower pressure the molecules will be further apart

so there will be fewer collisions per unit time

accept frequency of collisions lower

1

1

AO2

12f

5(b)(iii)

as the temperature increases, the yield of the reaction increases

1 AO2

12g

5(b)(iv)

2 molecules / volumes become 4 or more molecules / volumes of product than reactant

1 AO1

7d

Question 5 continues on the next page


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Question 5 continued

5(c) 6 marks 1AO1/2AO2/3AO3 1.1a, 8.3a, 8.3c, 8.3f

Marks awarded for this answer will be determined by the Quality of Communication (QoC) as well as the standard of the scientific response. Examiners should also refer to the information on page 5, and apply a best-fit approach to the marking.

0 marks Level 1 (12 marks) Level 2 (34 marks) Level 3 (56 marks)

No relevant content Candidate has written about some basic points from the table but has not added any extra knowledge. Candidate may have included advantages or disadvantages.

Candidate has attempted an evaluation using points from the table and their own knowledge. Candidate has included advantages and disadvantages.

Candidate has given an evaluation that includes both advantages and disadvantages. Candidate has clearly linked points from the table with their own knowledge and uses appropriate scientific terminology.

examples of the points made in the response Advantages of using hydrogen:

its combustion only produces water combustion of hydrogen does not

produce carbon dioxide or does not contribute to climate change

petrol requires much more oxygen to burn so partial combustion is possible producing carbon monoxide

combustion of hydrogen does not produce any particulates or does not contribute to global dimming

petrol comes from a non-renewable source or there are renewable ways of producing hydrogen, eg electrolysis of water.

Disadvantages of using hydrogen: hydrogen has to be stored at high

pressure or risk of explosion or larger volume needed for storage.

much less energy produced from the combustion of hydrogen or need to refuel more often

most methods of producing hydrogen need fossil fuels.

Total 13


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6(a)

magnesium loses electrons

two electrons

chlorine gains electrons

two atoms of chlorine

there are four ideas here that need to be linked in two pairs.

magnesium loses electrons and chlorine gains electrons scores 2 marks.

magnesium loses two electrons and two chlorines each gain one electron will score full marks.

1

1

1

1

2AO1/2AO2

2.1c

6(b)

95 correct answer with or without working gains 2 marks if answer incorrect, allow 24 + 35.5 + 35.5 for 1 mark

2 AO2

1.3b

Total 6


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7(a)(i)

ethanol 1 AO1

10.1a

7(a)(ii)

oxidised 1 AO1

10.1c

7(a)(iii)

Test add any named carbonate or hydrogen carbonate

Result A will effervesce (carbon dioxide) or B will not effervesce. or Test add a named (magnesium, aluminium, zinc, iron or tin) metal

Result A will effervesce (hydrogen), B will not

or Test add an acidbase indicator

Result credit any acid colour for that indicator eg for universal indicator allow red, yellow or orange

give credit for the neutral colour for B or Test add an alcohol (+ acid catalyst)

Result sweet or fruity smell of esters.

the first mark is for the test; the second is for the result

if the result is incorrect, award the first mark only

if the test is incorrect award 0 marks.

candidates do not have to name a gas but penalise an incorrect gas.

give credit to any test that will work.

allow a test that would identify B.

1

1

AO1/AO2

10.2b

Question 7 continues on the next page


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Question 7 continued


7(b)(i)

H2O 1 AO2

1.3f, 10.2b

7(b)(ii)

ethyl ethanoate 1 AO1

10.3a

7(b)(iii)

any one from:

flavourings

perfumes

solvents

plasticisers

allow any correct use of esters 1 AO1

10.3b

Total 7


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8(a)

any two from:

temperature (of the HCl) mass or length of the

magnesium surface area of the

magnesium volume of HCl

2 AO3

7d, 7f

8(b)(i)

(a greater concentration has) more particles per unit volume

therefore more collisions per unit time or more frequent collisions.

allow particles are closer together 1

1

AO1

7e

8(b)(ii)

particles move faster

therefore more collisions per unit time or more frequent collisions collisions more energetic (therefore more collisions have energy greater than the activation energy) or more productive collisions

allow particles have more (kinetic) energy

1

1

1

AO1

7c

8(c)(i)

add (a few drops) of indicator to the acid in the conical flask

add NaOH (from the burette) until the indicator changes colour or add the NaOH dropwise

repeat the titration

calculate the average volume of NaOH or repeat until concordant results are obtained

allow any named indicator

candidate does not have to state a colour change but penalise an incorrect colour change.

1

1

1

1

AO1

5.1h

8(c)(ii)

moles of NaOH 0.10 x 0.0272 = 0.00272 moles

Concentration of HCl 0.00272 / 0.005 = 0.544

correct number of significant figures

correct answer with or without working gains 3 marks

allow ecf from mp1 to mp2

1

1

1

AO2

5.1i

Total 14


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9(a)(i)

giant lattice

atoms in in graphene are covalently bonded

and covalent bonds are strong or need a lot of energy to be broken

allow each carbon atom is joined to three others

max. 2 marks if any reference to wrong type of bonding

allow difficult to break

1

1

1

1AO1/2AO2

2.2f

9(a)(ii)

because graphene has delocalised electrons

which can move throughout the structure

allow each carbon atom has one free electron

do not accept just electrons can move.

1

1

AO1/AO2

2.2i

9(b)

because there are weak forces between molecules

so layers / molecules can slip / slide.

allow no bonds between the layers 1

1

AO1

2.2h

Total 7


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10(a)

(24 x 12) x 100 = 67.6

426

or 426 x (67.6/100) = 288 288/12 = 24

1 AO2

1.3d

10(b)

5.65/12 2.2/14 0.629/1

0.471 0.157 0.629

3 1 4

C3NH4

correct answer of C3NH4 with no working scores 2 marks allow ecf from mp2 onwards

if the ratios are not shown but the correct working is shown for mp1 and mp2 , the ratio mark can be scored from C3NH4 if the initial fractions are inverted and the candidate gets an answer of C4N12H3 award 2 marks

1

1

1

1

AO2

1.3e

Total 5


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11(a)

products are at a lower energy level than reactants

activation energy correctly drawn and labelled

H correctly labelled

if candidate has drawn a profile for an endothermic reaction penalise first marking point only

1

1

1

2AO1/1AO2

11.2d

11(b)(i)

93 (kJ per mole)

correct answer with or without working gains 3 marks allow 2 marks for +93 kJ per mole if any other answer is seen award up to 2 marks for any two of the steps below:

bonds broken (614 + 193) = 807 (kJ) or (614 + 193 + (4 x 413)) = 2459(kJ)

bonds formed (348 + 276 + 276) = 900(kJ) or 348 + (2 x 276) + (4 x 413) = 2552(kJ)

bonds broken bonds formed

allow ecf for arithmetical errors

3 AO2

11.2e

11(b)(ii)

more energy is released when the bonds (in the products) are formed

than is needed to break the bonds (in the reactants)

if no other marks gained, allow 1 mark for energy released for bond making and energy used for bond breaking

1

1

AO1

11.2f

Total 8

AQA Level 1/2 Certificate

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