A-Level EDEXCEL 2025 Chemistry PAPER 1 Mark Scheme
Mark Scheme (Results)
Summer 2025
Pearson Edexcel GCE A Level In Chemistry (9CH0) Paper 01: Advanced Inorganic and
Physical Chemistry
Using the Mark Scheme
Examiners should look for qualities to reward rather than faults to penalise. This does NOT mean giving credit for incorrect or inadequate
answers, but it does mean allowing candidates to be rewarded for answers showing correct application of principles and knowledge.
Examiners should therefore read carefully and consider every response: even if it is not what is expected it may be worthy of credit.
The mark scheme gives examiners:
an idea of the types of response expected
how individual marks are to be awarded
the total mark for each question
examples of responses that should NOT receive credit.
/ means that the responses are alternatives and either answer should receive full credit.
( ) means that a phrase/word is not essential for the award of the mark, but helps the examiner to get the sense of the expected answer.
Phrases/words in bold indicate that the meaning of the phrase or the actual word is essential to the answer.
ecf/TE/cq (error carried forward) means that a wrong answer given in an earlier part of a question is used correctly in answer to a later part
of the same question.
Candidates must make their meaning clear to the examiner to gain the mark. Make sure that the answer makes sense. Do not give credit for
correct words/phrases which are put together in a meaningless manner. Answers must be in the correct context.
,Quality of Written Communication
Questions which involve the writing of continuous prose will expect candidates to:
write legibly, with accurate use of spelling, grammar and punctuation in order to make the meaning clear
select and use a form and style of writing appropriate to purpose and to complex subject matter
organise information clearly and coherently, using specialist vocabulary when appropriate. Full
marks will be awarded if the candidate has demonstrated the above abilities.
Questions where QWC is likely to be particularly important are indicated (QWC) in the mark scheme, but this does not preclude others.
,Question
Number Answer Additional Guidance Mark
1(a) An answer that makes reference to the following points: (2)
(relative isotopic mass) is the mass of an atom (of the (1) Allow mass of an isotope of an atom
isotope / element)
Do not award any reference to average / mean /
weighted or moles in M1 or M2, but penalise
only once if in both
relative to 1/12th (the mass of an atom) of carbon‒12 (1) Allow for two marks
Mass of one atom of an isotope × 12
Mass of one atom of carbon-12
COMMENT M1 can be awarded if atom
mentioned somewhere in response
, Question
Answer Additional Guidance Mark
Number
1(b) An answer that makes reference to the following points: (2)
all isotopes have 18 protons (and 18 electrons) (1) Do not award incorrect number of electrons
the isotopes have different numbers of neutrons, 18, Isotope Protons Neutrons
20 and 22 (1)
36Ar 18 18
38Ar 18 20
40Ar 18 22
If no other mark awarded allow isotopes have the
same number of protons but a different number of
neutrons for 1 mark
Ignore same atomic number and different mass
number
Mark Scheme (Results)
Summer 2025
Pearson Edexcel GCE A Level In Chemistry (9CH0) Paper 01: Advanced Inorganic and
Physical Chemistry
Using the Mark Scheme
Examiners should look for qualities to reward rather than faults to penalise. This does NOT mean giving credit for incorrect or inadequate
answers, but it does mean allowing candidates to be rewarded for answers showing correct application of principles and knowledge.
Examiners should therefore read carefully and consider every response: even if it is not what is expected it may be worthy of credit.
The mark scheme gives examiners:
an idea of the types of response expected
how individual marks are to be awarded
the total mark for each question
examples of responses that should NOT receive credit.
/ means that the responses are alternatives and either answer should receive full credit.
( ) means that a phrase/word is not essential for the award of the mark, but helps the examiner to get the sense of the expected answer.
Phrases/words in bold indicate that the meaning of the phrase or the actual word is essential to the answer.
ecf/TE/cq (error carried forward) means that a wrong answer given in an earlier part of a question is used correctly in answer to a later part
of the same question.
Candidates must make their meaning clear to the examiner to gain the mark. Make sure that the answer makes sense. Do not give credit for
correct words/phrases which are put together in a meaningless manner. Answers must be in the correct context.
,Quality of Written Communication
Questions which involve the writing of continuous prose will expect candidates to:
write legibly, with accurate use of spelling, grammar and punctuation in order to make the meaning clear
select and use a form and style of writing appropriate to purpose and to complex subject matter
organise information clearly and coherently, using specialist vocabulary when appropriate. Full
marks will be awarded if the candidate has demonstrated the above abilities.
Questions where QWC is likely to be particularly important are indicated (QWC) in the mark scheme, but this does not preclude others.
,Question
Number Answer Additional Guidance Mark
1(a) An answer that makes reference to the following points: (2)
(relative isotopic mass) is the mass of an atom (of the (1) Allow mass of an isotope of an atom
isotope / element)
Do not award any reference to average / mean /
weighted or moles in M1 or M2, but penalise
only once if in both
relative to 1/12th (the mass of an atom) of carbon‒12 (1) Allow for two marks
Mass of one atom of an isotope × 12
Mass of one atom of carbon-12
COMMENT M1 can be awarded if atom
mentioned somewhere in response
, Question
Answer Additional Guidance Mark
Number
1(b) An answer that makes reference to the following points: (2)
all isotopes have 18 protons (and 18 electrons) (1) Do not award incorrect number of electrons
the isotopes have different numbers of neutrons, 18, Isotope Protons Neutrons
20 and 22 (1)
36Ar 18 18
38Ar 18 20
40Ar 18 22
If no other mark awarded allow isotopes have the
same number of protons but a different number of
neutrons for 1 mark
Ignore same atomic number and different mass
number
