GCSE Chemistry Mark scheme Unit 03 - Chemistry June 2015

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GCSE Chemistry Mark scheme Unit 03 - Chemistry June 2015

Transcript Of GCSE Chemistry Mark scheme Unit 03 - Chemistry June 2015

GCSE Chemistry
CH3HP Mark scheme
4402 June 2015
Version/Stage: 1.0 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 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
Copyright © 2015 AQA and its licensors. All rights reserved. AQA retains the copyright on all its publications. However, registered schools/colleges for AQA are permitted to copy material from this booklet for their own internal use, with the following important exception: AQA cannot give permission to schools/colleges to photocopy any material that is acknowledged to a third party even for internal use within the centre.

MARK SCHEME – GCSE CHEMISTRY – CH3HP – JUNE 2015
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 Assessment Objectives and specification content that each question is intended to cover. 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 and underlining 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. 2.4 Any wording that is underlined is essential for the marking point to be awarded.
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 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.
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MARK SCHEME – GCSE CHEMISTRY – CH3HP – JUNE 2015

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

Student
1 2 3

Response
green, 5 red*, 5 red*, 8

Marks awarded
0 1 0

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

Student 1 2

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

Marks awarded 1 0

3.2 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, 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 is 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 or insufficient are 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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MARK SCHEME – GCSE CHEMISTRY – CH3HP – JUNE 2015
Quality of Written Communication and levels marking In Question 4(b) 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.
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MARK SCHEME – GCSE CHEMISTRY – CH3HP – JUNE 2015

Question

Answers

1(a) Li and K

1(b) Fe

1(c) N and As

1(d) Cu

Total

Extra information either order allow lithium and potassium allow iron
either order allow nitrogen and arsenic allow copper

Mark

AO /

Spec. Ref.

1 AO1 3.1.3.a

1 AO1 3.5.1.b

1 AO2 3.1.2.b

1 AO1 3.1.3.d

4

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MARK SCHEME – GCSE CHEMISTRY – CH3HP – JUNE 2015

Question

Answers

2(a) (iron) is a metal

Extra information

Mark

AO /

Spec. Ref.

accept transition element

1 AO2

allow (iron) had different properties (to oxygen and sulfur)

3.1.1.a

ignore electrons

2(b) so that elements with similar properties could be placed together

allow to make the pattern fit ignore undiscovered elements

1 AO1 3.1.1.b

2(c) atomic number(s)

allow proton number(s)

1 AO1 3.1.2.a

2(d) all have one electron in the

allow same number of electrons

outer shell (highest energy level) in the outer shell (highest

energy level)

1 AO1 3.1.2.b

(so they) have similar properties

1

or

react in the same way

allow specific reactions e.g. with water

Total

5

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MARK SCHEME – GCSE CHEMISTRY – CH3HP – JUNE 2015

Question

Answers

3(a) increase

3(b)(i) Na+ and Br–

3(b)(ii) sodium chloride

3(b)(iii)

chlorine is more reactive than bromine

3(b)(iv) fluorine Total

Extra information

Mark

AO /

Spec. Ref.

1 AO1 3.1.3.f

both required

1 AO1 3.1.3.a/e

allow NaCl do not allow sodium chlorine

1 AO2 3.1.3.g

allow converse argument

1 AO1

allow symbols Cl, Cl2, Br and Br2

3.1.3.g

allow chlorine / it is more reactive.

do not allow chloride or bromide

allow F / F2. do not allow fluoride.

1 AO2 3.1.3.g

5

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MARK SCHEME – GCSE CHEMISTRY – CH3HP – JUNE 2015

Question

Answers

4(a) (calcium or magnesium) ions causing water hardness are dissolved
from rocks

Extra information ignore named anions allow limestone

Mark AO / Spec. Ref.
1 AO1/ AO2 3.2.1.b
1

4(b) 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 5, and apply a ‘best-fit’ approach to the marking.

AO1/ AO3 3.2.1.g 3.2.2.b

0 marks
No relevant content

Level 1 (1–2 marks)
There is a statement about one of the methods or one advantage of one of the methods

Level 2 (3–4 marks)
There is a description of one method of water softening and one advantage of a method is given

Level 3 (5–6 marks)
There is a description of both methods of water softening and a comparison of the two methods by giving an advantage of at least one of them

general:
• hard water contains calcium/magnesium (ions) • softening water involves removal of calcium/magnesium (ions)

ion exchange: • resin • contains sodium/hydrogen ions • which are exchanged with calcium/magnesium ions • resin needs periodic replenishment with sodium ions/hydrogen ions or sodium
chloride (disadvantage) • increases sodium content of water (if sodium ions used) (disadvantage) • easy/quick method to use (advantage) • continuous process (advantage)

sodium carbonate: • sodium carbonate is added to hard water • calcium/magnesium ions precipitate out • as calcium/magnesium carbonate • batch process (disadvantage) • leaves a residue of precipitated carbonate in the water (disadvantage) • increases sodium content of water (disadvantage) • easy method to use (advantage) • relatively cheap (advantage)

Total

8

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Question

Answers

5(a) any two from: • fuel • solvent • antiseptic

Extra information
allow source of energy allow perfume / aftershave allow antibacterial

Mark

AO /

Spec. Ref.

2 AO1 3.6.1.b

5(b) Hydrogen

5(c)(i) oxidation

do not allow redox

5(c)(ii) correct structure

5(c)(iii)

ethanoic acid is a weak / weaker acid
because it does not completely ionise.

it = ethanoic acid
allow because it does not completely dissociate allow it has a lower concentration of hydrogen ions allow converse for hydrochloric acid do not allow ionising

5(d)(i) ethyl ethanoate

5(d)(ii) acid 5(d)(iii) evaporates easily / quickly Total

allow any strong acid allow correct formulae
allow low boiling point do not allow flammable

1 AO1 3.6.1.b
1 AO1 3.6.1.c
1 AO1 3.6.2.a AO1/ AO2
1 3.6.2.b 1
1 AO1 3.6.2.b
1 AO1 3.6.2.b
1 AO1 3.6.3.a
10

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AnswerMark SchemeMarksWaterAdvantage