Here’s something that surprises students: most marks lost in A‑level chemistry aren’t lost because the student didn’t know the chemistry. They’re lost to avoidable exam mistakes — the same handful, paper after paper. As an official examiner for many years, I’ve marked these errors thousands of times. The good news? Every one is fixable. Here are the top ten.
1. Not reading the command word
Describe, explain, compare, evaluate, suggest — each demands a different type of answer. Students who “explain” when asked to “describe” (or vice versa) cap their own marks instantly. Fix: underline the command word before writing. (More in my 6‑mark technique post.)
2. Losing the units on the rate constant (and elsewhere)
Kinetics questions routinely ask for the rate constant k — and students find the number but drop or guess the units. Units change with the overall order and are worth marks. Fix: always derive units by cancelling them in the rearranged equation.
3. Sloppy curly arrows in mechanisms
An arrow that starts in the wrong place — from a positive charge instead of an electron pair, or from the wrong atom — loses marks even when the products are right. Fix: every curly arrow starts from a bond or lone pair and points to where the new bond forms. Precision, every time. (See my mechanisms post.)
4. Vague, imprecise language
“The particles stick together” scores nothing; “strong electrostatic forces of attraction between oppositely charged ions” scores the mark. Mark schemes reward exact terminology. Fix: learn the precise words each topic demands — delocalised, electrostatic, intermolecular, exothermic, equilibrium.
5. Not showing working in calculations
A bare final answer that’s wrong scores zero; the same wrong answer with clear working often earns most of the method marks. Fix: show every step, keep units in, and round only at the end.
6. Rounding too early
Rounding intermediate values and carrying them forward introduces errors that can cost the final accuracy mark. Fix: keep full precision on your calculator throughout and round only the final answer to the required significant figures.
7. Sign errors in energetics
Born‑Haber and enthalpy questions are riddled with lost marks from positive/negative slips. Fix: draw the energy‑level diagram — up is endothermic (+), down is exothermic (−). It’s much harder to get a sign wrong when you can see the arrow’s direction. (See my Born‑Haber post.)
8. Trying to read reaction orders off the balanced equation
Orders come from experimental data only — never from the stoichiometry of the equation. Students who assume otherwise get the rate equation wrong from the start. Fix: always determine orders by changing one concentration at a time and observing the rate.
9. Forgetting to conclude on “evaluate” questions
Students lay out every advantage and disadvantage — then forget the final judgement, throwing away the easiest mark. Fix: on evaluate/compare questions, always end with “Overall, … because …”.
10. Poor time management and blank extended answers
Running out of time, or freezing on the big 6‑mark question and leaving it blank, quietly costs the most. An extended question left empty is a guaranteed zero; a structured attempt almost always scores something. Fix: watch the clock (roughly a mark a minute), and always attempt every part — a planned answer beats a blank box every time.
The pattern behind all ten
Notice that almost none of these are about knowing more chemistry. They’re about technique — reading the question, being precise, showing working, and managing the paper. That’s exactly why exam practice with proper feedback lifts grades so quickly: you’re plugging the leaks, not relearning the subject.
A quick self‑check before your next mock
- [ ] Did I underline every command word?
- [ ] Did I show full working with units?
- [ ] Are my curly arrows starting from bonds/lone pairs?
- [ ] Did I use precise chemical vocabulary?
- [ ] Did I draw diagrams for energetics?
- [ ] Did I conclude on evaluate questions?
- [ ] Did I attempt every question?
The bottom line
The students who jump a grade often don’t learn more chemistry — they stop making these ten mistakes. Precision, working, and exam technique are where the marks hide.
As an examiner, spotting and fixing exactly these errors in your work is one of the most valuable things I do in a lesson — I can show you precisely where your marks are leaking.
👉 Book a free intro call and let’s plug the leaks before your next exam.