Common Chemistry Exam Mistakes (and How to Avoid Them)

Physical chemistry calculations are marked on method as much as the final answer. A correct final number with no working shown can lose most of the available marks if the method itself isn't visible - and a wrong final answer with clearly correct method can still pick up the majority of them. Always show every step, even ones that feel obvious.

Chemistry mark schemes are unusually strict about definitions. 'Rate of reaction' has a precise definition involving change in concentration over time - describing it loosely as 'how fast a reaction goes' will not get the mark, even though it's not wrong in everyday language. The fix is simple but easy to skip: learn the exact wording examiners are looking for, not just the general idea.

'State', 'describe', 'explain' and 'deduce' all require different kinds of answers, and mark schemes are built around that difference. Writing an explanation when the question only asks the student to state a fact wastes time; writing a bare statement when the question asks for an explanation loses marks. Reading the command word before writing anything is one of the highest-value habits a student can build.

Getting stuck on one difficult question and running out of time for several easier ones later in the paper is one of the most common - and most avoidable - ways marks are lost. A quick glance at the mark allocation for each question before starting helps decide how long to spend, and it's almost always worth moving on from a stuck question and returning to it at the end.

A numerically correct answer without the correct unit, or given to the wrong number of significant figures, routinely loses a mark that has nothing to do with whether the chemistry was understood. This is one of the easiest categories of lost marks to eliminate entirely with a simple habit: check units and significant figures on every calculation answer, every time.

At A Level in particular, similar-looking mechanisms - nucleophilic substitution versus elimination, for example - are easy to blur together under exam pressure without deliberate, repeated practice telling them apart. The fix isn't memorising more mechanisms; it's practising identifying which mechanism applies to a given scenario before drawing anything.