PDF
Mark Scheme (Results)
Summer 2026
Pearson Edexcel Advanced Level in Chemistry
9CH0/03
,Edexcel and BTEC Qualifications
Edexcel and BTEC qualifications are awarded by Pearson, the UK’s
largest awarding body. We provide a wide range of qualifications
including academic, vocational, occupational and specific
programmes for employers. For further information visit our
qualifications websites at www.edexcel.com or www.btec.co.uk.
Alternatively, you can get in touch with us using the details on our
contact us page at www.edexcel.com/contactus
Pearson: helping people progress, everywhere
Pearson aspires to be the world’s leading learning company. Our aim is to help
everyone progress in their lives through education. We believe in every kind of
learning, for all kinds of people, wherever they are in the world. We’ve been
involved in education for over 150 years, and by working across 70 countries, in
100 languages, we have built an international reputation for our commitment to
high standards and raising achievement through innovation in education. Find
out more about how we can help you and your students at:
www.pearson.com/uk
Summer 2026
Question Paper Log Number P83918A
Publication Code 9CH0_03_2606_MS
All the material in this publication is copyright
© Pearson
,General Marking Guidance
• All candidates must receive the same treatment. Examiners must mark the
first candidate in exactly the same way as they mark the last.
• Mark schemes should be applied positively. Candidates must be rewarded
for what they have shown they can do rather than penalised for omissions.
• Examiners should mark according to the mark scheme not according to their
perception of where the grade boundaries may lie.
• There is no ceiling on achievement. All marks on the mark scheme should be
used appropriately.
• All the marks on the mark scheme are designed to be awarded. Examiners
should always award full marks if deserved, i.e. if the answer matches the
mark scheme. Examiners should also be prepared to award zero marks if the
candidate’s response is not worthy of credit according to the mark scheme.
• Where some judgement is required, mark schemes will provide the principles
by which marks will be awarded and exemplification may be limited.
• When examiners are in doubt regarding the application of the mark scheme
to a candidate’s response, the team leader must be consulted.
• Crossed out work should be marked UNLESS the candidate has replaced it
with an alternative response.
, Question Mark
Answer Additional Guidance
Number
1(a) An explanation that makes reference to the following Ignore reference to electrons (2)
points:
• mass number includes the number of neutrons, (1)
which is different for isotopes
• (whereas) atomic number is the number of (1)
protons, and isotopes have the same number of
protons If no other mark awarded allow one mark for isotopes have the same
number of protons but different numbers of neutrons
Question Mark
Answer Additional Guidance
Number
1(b) Example of calculation (2)
• correct expression for calculation of Ar (1) Ar = ((19.99 × 90.48) + (20.99 × 0.27) + (21.99 × 9.25))
100
Ar = (20.1777)
• relative atomic mass to 2 dp (1) Ar = 20.18
TE on correct calculation from transposed numbers
Ignore units of g mol−1 / AMU but penalise any other units
Correct answer without working scores (2)
20.2 without working scores 0
Mark Scheme (Results)
Summer 2026
Pearson Edexcel Advanced Level in Chemistry
9CH0/03
,Edexcel and BTEC Qualifications
Edexcel and BTEC qualifications are awarded by Pearson, the UK’s
largest awarding body. We provide a wide range of qualifications
including academic, vocational, occupational and specific
programmes for employers. For further information visit our
qualifications websites at www.edexcel.com or www.btec.co.uk.
Alternatively, you can get in touch with us using the details on our
contact us page at www.edexcel.com/contactus
Pearson: helping people progress, everywhere
Pearson aspires to be the world’s leading learning company. Our aim is to help
everyone progress in their lives through education. We believe in every kind of
learning, for all kinds of people, wherever they are in the world. We’ve been
involved in education for over 150 years, and by working across 70 countries, in
100 languages, we have built an international reputation for our commitment to
high standards and raising achievement through innovation in education. Find
out more about how we can help you and your students at:
www.pearson.com/uk
Summer 2026
Question Paper Log Number P83918A
Publication Code 9CH0_03_2606_MS
All the material in this publication is copyright
© Pearson
,General Marking Guidance
• All candidates must receive the same treatment. Examiners must mark the
first candidate in exactly the same way as they mark the last.
• Mark schemes should be applied positively. Candidates must be rewarded
for what they have shown they can do rather than penalised for omissions.
• Examiners should mark according to the mark scheme not according to their
perception of where the grade boundaries may lie.
• There is no ceiling on achievement. All marks on the mark scheme should be
used appropriately.
• All the marks on the mark scheme are designed to be awarded. Examiners
should always award full marks if deserved, i.e. if the answer matches the
mark scheme. Examiners should also be prepared to award zero marks if the
candidate’s response is not worthy of credit according to the mark scheme.
• Where some judgement is required, mark schemes will provide the principles
by which marks will be awarded and exemplification may be limited.
• When examiners are in doubt regarding the application of the mark scheme
to a candidate’s response, the team leader must be consulted.
• Crossed out work should be marked UNLESS the candidate has replaced it
with an alternative response.
, Question Mark
Answer Additional Guidance
Number
1(a) An explanation that makes reference to the following Ignore reference to electrons (2)
points:
• mass number includes the number of neutrons, (1)
which is different for isotopes
• (whereas) atomic number is the number of (1)
protons, and isotopes have the same number of
protons If no other mark awarded allow one mark for isotopes have the same
number of protons but different numbers of neutrons
Question Mark
Answer Additional Guidance
Number
1(b) Example of calculation (2)
• correct expression for calculation of Ar (1) Ar = ((19.99 × 90.48) + (20.99 × 0.27) + (21.99 × 9.25))
100
Ar = (20.1777)
• relative atomic mass to 2 dp (1) Ar = 20.18
TE on correct calculation from transposed numbers
Ignore units of g mol−1 / AMU but penalise any other units
Correct answer without working scores (2)
20.2 without working scores 0
