IGCSE & GCSE Chemistry Examiners' Edition: Common Mistakes by Topic (Edexcel)

Examiners’ Edition · Edexcel IGCSE & GCSE Chemistry

Aiming for a grade 9? Stop losing easy marks.

Most marks aren’t lost on the hardest questions. They’re lost to the same small mistakes examiners flag year after year. We’ve gone through the Pearson Edexcel International GCSE and GCSE Chemistry papers and examiners’ reports and pulled out the mistakes that cost the most marks in every topic.

See the mistake examiners flag year after year, topic by topic.
Learn the fix, and what examiners saw in the exam.
Practise and mark it with original questions and full mark schemes.

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Written by Mr M Khan, Chemistry Lead, former pharmacist and former Principal

IGCSE & GCSE Chemistry · Topic 1

Principles of Chemistry

Examiners’ Edition: Securing Grade 9s

21 common mistakes · 42 practice questions · full mark schemes

1.1 States of matter, mixtures and separation All students

1 Melting points and purity

✗ Common mistake

Saying an impure substance has a “different” or “higher” melting point, without saying it melts over a range of temperatures.

✓ Do this instead

A pure substance melts (or boils) at one exact, fixed temperature. An impure substance (a mixture) melts over a range of temperatures, usually below the pure melting point.

In the exam

“Only a very small minority stated that an impure substance melts over a range of temperatures.” Jan 2021, 1C

Examiners flagged this in 3 exam series, 2020 to 2022

Question 1.1 · Check itMark scheme ›3

Pure aspirin melts at 135 °C. A student’s sample of aspirin melts between 128 °C and 133 °C. Explain whether the student’s sample is pure. (2)

Mark scheme · Q1.1‹ Back to question

the sample is not pure (it is impure)1

it melts over a range of temperatures, below 135 °C (not at a fixed temperature)1

Common wrong answer: “the melting point is lower” scores only half: the key idea is a range, not one fixed value.

Real pages from Topic 1. Every topic is laid out like this.

Topics: 4
Common mistakes fixed: 63
Practice questions: 126
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Pearson Edexcel International GCSE & GCSE Chemistry · 4CH1, 1CH0, 1SC0

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IGCSE & GCSE sample

IGCSE & GCSE

Topics 1 to 4

Every mistake is marked for your course: International GCSE, GCSE Chemistry or Combined Science, and Higher tier.

£1

Topic 1

Principles of Chemistry

21 mistakes fixed42 practice questions

£1

Topic 2

Inorganic Chemistry

16 mistakes fixed32 practice questions

£1

Topic 3

Physical Chemistry

10 mistakes fixed20 practice questions

£1

Topic 4

Organic Chemistry

16 mistakes fixed32 practice questions

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