A Level Chemistry: The Most Common Exam Mistakes

By Russell Greenhill

Founder & CEO @ Greenhill Academics

Oxford Master’s Graduate • 8+ Years Tutoring Experience

What the examiner reports tell parents

If your child is sitting A Level Chemistry, you need to know what the most common exam mistakes are and how they can avoid them. You may have looked at their past paper scripts and wondered why the grade is not matching the effort. The answer is usually in the examiner reports, which the exam boards publish for free after every sitting.

These reports reveal the most common A Level Chemistry exam mistakes year after year, and the pattern is clear. Marks are rarely lost on big gaps in knowledge. They are lost on small habits: a missed symbol, a wrong sign, a phrase that meant the right thing in everyday English but the wrong thing in chemistry. The chemistry was usually right. The way it landed on the page let the student down.

Why your child can know the content and still lose marks

A Level Chemistry rewards precision. The difference between an answer scoring four out of five and one scoring full marks is often a single word, a state symbol, or a sign. Spotting these slips in your own work is genuinely hard, because the answer looks right to the person who wrote it.

The examiner reports give parents an unusual window into what is actually rewarded. They are written for teachers, but the picture they paint is one any parent can use. As a result, the same A Level Chemistry exam mistakes recur every year, because most students never read the reports and so never know what the examiner is really looking for.

The most common A Level Chemistry exam mistakes

Equations that do not quite work

Chemistry exams ask students to write chemical equations. Examiners flag two recurring problems. First, students miss the small symbols that show whether something is a solid, liquid, or gas. Second, they get so focused on making the numbers balance that they forget to check whether the resulting answer could actually exist.

For example, in one June 2024 AQA question, a surprising number of students wrote down a chemical formula that, taken at face value, would describe a molecule that simply cannot be made. They had balanced the maths and forgotten the chemistry. A quick read-back of every equation catches this.

Sign errors and calculation slips

Around 20% of A Level Chemistry marks come from calculations. However, the errors are rarely in the maths itself. Instead they are in the setup: forgetting to convert units, dropping a power of ten, or rearranging an equation the wrong way.

The classic example is the sign error. Chemistry answers often come with a plus or minus that shows whether energy is being released or absorbed. In a 2024 AQA calculation, around 40% of students scored full marks. Many of the rest had the maths perfectly right but wrote a plus sign where there should have been a minus, and lost the final mark for it. An experienced eye catches this in seconds. A student under exam pressure misses it.

Mechanism diagrams drawn slightly wrong

In organic chemistry, students draw step-by-step diagrams showing how a reaction works, with arrows that have to start and finish in exactly the right places. For instance, in a 2024 AQA question, over 80% of students got at least one mark, but only 32% got all three. The arrows were close. Not quite right.

The examiner noted that this same kind of mistake had been flagged “many times” in past reports. In practice, students keep making it because most of them never read the reports. A specialist can spot the issue in five minutes of looking at your child’s work.

Right idea, wrong words

Many A Level Chemistry questions ask for an explanation. The mark scheme is specific about which words score. Students who use everyday phrases to describe a chemical idea often lose marks, even when they clearly understand what is going on.

In one 2024 question, examiners reported that the “care needed in use of language” was what separated the top answers from the rest. Two students could give answers that meant the same thing. Only one would score, because only one used the precise term the mark scheme rewards. This is one of the easiest A Level Chemistry exam mistakes to fix, but only once your child knows which terms matter.

Practical questions treated as background noise

At least 15% of marks on the written papers come from practical work: questions on lab equipment, techniques, and observations. These are usually straightforward facts from the syllabus, but they slip through if practical work has been treated as a chore during the year.

For example, in June 2024, only around 30% of students could answer a basic question on what indicates that a sample is pure. That kind of fact lives quietly in the specification and quietly costs a grade if it has not been learnt.

Misreading the command word

“Describe”, “explain”, “suggest”, and “state” each call for a different style of answer. Students who write an explanation when the question asks for a description lose marks. Students who refuse to commit to an answer on a “suggest” question because they have not seen the example before also lose marks.

The fix is a single habit: highlight the command word on every question before writing. It takes ten seconds and saves marks across the paper.

How to fix these A Level Chemistry exam mistakes

Look for the pattern, not the topic

When your child loses marks on a past paper, the question to ask is not “what topic was that on?” but “what type of mistake was that?” Two questions on completely different topics can both be lost to the same habit. Once your child sees the habit, they can fix it across the whole paper.

Have them mark their own past papers properly

Doing past papers is helpful. Marking them carefully is where the gain comes from. After every paper, your child should sit with the mark scheme open and identify every mark they did not get. Was the chemistry wrong, or was it a technique slip? The pattern usually appears within three or four papers. Our piece on A Level revision strategies that work covers complementary methods.

Get a second pair of eyes on their work

Self-marking has a ceiling. The student who wrote an answer is the worst-placed person to spot what is wrong with it, because the answer looks right to them. A specialist tutor reads the work line by line and identifies precisely where marks are being dropped. The same diagnostic eye comes up in our piece on the challenges of A Level Biology.

Meet some of our A Level Chemistry tutors

Gonzalo

Gonzalo read Chemistry at Jesus College, University of Oxford, graduating with a First (80% overall). He won the Woodward Prize for excellence in Chemistry three times. At A Level he earned A*s in Chemistry, Maths, Further Maths, and Biology, with nine 9s at GCSE. He starts a PhD in Inorganic Chemistry at the University of Cambridge soon. Gonzalo is exceptional at teaching the precision of language and notation that distinguishes A* answers from A answers.

Murray

Murray reads Materials Science at Trinity College, University of Oxford, where he is in his fourth year and expected to graduate with a First. At A Level he earned A*s in Chemistry, Maths, and Physics. His chemistry credentials include the Silver Cambridge Chemistry Award and the Armourers and Brasiers Award (top of his Oxford cohort). With over 150 hours of tutoring under his belt, Murray is particularly strong on the maths-heavy parts of A Level Chemistry that catch students out.

Want your child to stop losing marks in A Level Chemistry?

If your child knows the content but the grades are not yet reflecting it, the gap is almost certainly in technique. Get in touch and we will match them with a specialist A Level Chemistry tutor who can diagnose the issue and fix it before the next paper.

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