Chemistry difficulty concentrates in three places: mole calculations, bonding and structure, and organic mechanisms. They fail for different reasons and are taught well in different ways. A session that treats all three as “chemistry revision” will help with none of them properly.
The three places it goes wrong
Moles. The single largest source of lost marks in secondary and JC chemistry. The concept is straightforward and the application is not — students who can define a mole cannot reliably work through a multi-step stoichiometry problem under time.
The usual cause is that the mole was learned as a formula triangle rather than as a counting unit. A student who genuinely understands that a mole is a number of particles can reason through an unfamiliar problem. A student who memorised the relationships is fine until the question is phrased in a way that does not signal which formula to use.
Bonding and structure. Abstract, invisible, and taught in a way that often stops at classification. Students learn to label bonds ionic or covalent and cannot explain why a substance has the melting point it has. Exam questions ask the second thing.
Organic mechanisms. Volume plus pattern recognition. Students try to memorise every reaction as a separate fact, which does not scale, rather than learning the small number of underlying behaviours that generate most of them.
What good teaching of each looks like
For moles: the tutor should make the student narrate the reasoning, not the formula. “What are we counting? How many of them? What does the equation say about the ratio?” A student who can talk through it in those terms will handle unfamiliar problems. One who says “n equals m over M” is reciting.
Watch for whether practice includes multi-step problems where the required route is not obvious. Single-step drilling produces false confidence.
For bonding: look for teaching that connects structure to property. Not “this is a giant ionic lattice” but “this is a giant ionic lattice, therefore the melting point is high, because breaking it requires overcoming many strong attractions”. That causal chain is the answer the mark scheme wants, and it is teachable directly.
For organic: look for pattern-based teaching. Grouping reactions by what is happening — what attacks what, what leaves — rather than by memorising each transformation. Students who see the patterns can predict unfamiliar reactions; students who memorised cannot.
The session shape that works
The student attempts a problem cold while the tutor watches. In chemistry this is especially diagnostic, because the failure point in a multi-step calculation is precise and visible.
Working is written fully. Chemistry marks method. A student who does calculations mentally and writes only the answer loses marks that were available even when the answer is wrong.
Units and significant figures are checked out loud, every time, until it becomes automatic. This is unglamorous and it recovers a meaningful number of marks.
Equations are balanced properly, not approximately. A wrong ratio invalidates everything downstream, and it is a common silent error.
The student redoes a question alone before the session ends. Watching a mole calculation being solved produces the feeling of understanding; reproducing it cold is the test.
The practical component
Chemistry practical and data-response questions carry steady marks and reward preparation more than talent — experimental design, sources of error, reliability, interpreting unfamiliar apparatus.
Students under-prepare for this because it feels less like “real chemistry” than the calculations. It is among the more reliably improvable parts of the subject, and worth explicit session time.
The O-Level to A-Level step
H2 Chemistry increases abstraction sharply — energetics, equilibria, kinetics, more demanding organic. Two things catch students.
The first is that the mathematics becomes less avoidable. A student who compensated at O-Level for weak calculation confidence finds that harder at H2.
The second is that explanation precision matters more. The same idea expressed loosely earns less, and chemistry is strict about the difference between describing and explaining.
If a student did well at O-Level and is struggling at H2, it is usually one of those two, and both are addressable — but they need identifying first.
The check that catches most calculation errors
Students lose marks in mole calculations they could have caught themselves, and the reason is that nobody taught them what checking looks like beyond redoing the arithmetic.
Check the units first, not the number. If the working produces grams where moles per cubic decimetre were wanted, the setup was wrong and no amount of recalculating will fix it. Units carried through each line make this visible immediately.
Check the magnitude against the physical situation. A product mass larger than the total mass of the reactants is impossible. A concentration of several hundred moles per cubic decimetre is not a real solution. These take two seconds to notice and students rarely look.
Check the ratio came from a balanced equation. The single most common source of a confidently wrong answer, and it is caught by looking at one line of working.
Check which reactant actually limits the reaction, where two quantities are given. If a question supplies two masses, it is usually asking this, and a student who uses the wrong one produces a tidy answer to a different question.
A student who runs these four checks routinely converts a large share of near-misses into marks, and none of them require any additional chemistry.
Equations: derive rather than remember
The distinction decides whether a student can handle an unfamiliar substance, so it is worth being concrete about what deriving means.
Ask what is actually present. In solution, ionic compounds exist as separate ions. Writing the full formula where ions were wanted, or the reverse, is the usual first error.
Ask which of those actually change. Spectator ions are present and unchanged, and identifying them is most of what an ionic equation asks.
Ask what the driving force is — a precipitate forming, a gas escaping, water being produced. That tells you what the products must be without recalling the specific reaction.
Then balance, and check the charges balance too, not only the atoms. Charge imbalance is a frequent and easily-caught error.
A student who works this way can write an equation for a reaction they have never studied. A student who memorised a list cannot, and that difference is what separates grades when the paper introduces something unfamiliar.
How to tell it is working
- Can they start an unfamiliar calculation without asking which formula to use?
- Do they write full working without being prompted?
- Can they explain a property from a structure, rather than just naming the structure?
- Do they check units and significant figures unprompted?
Those four move before the grade does, and if none has shifted in a term, the sessions are probably explanation-heavy and practice-light.
Frequently asked questions
My child understands chemistry in class but fails tests. Why? Usually the gap between following a worked calculation and producing one alone under time. Following is a much lower bar. Ask them to do a mole problem with you watching but not helping.
Is chemistry harder than physics? They fail differently. Physics punishes weak mathematics; chemistry punishes weak precision in both calculation and written explanation. Students usually find one clearly harder depending on which is their weakness.
How much does organic chemistry matter? Enough that memorising it is a losing strategy at A-Level. The volume is too large. Pattern-based understanding is the only approach that scales.
Should we focus on past papers or on content? Past papers, marked strictly, once the content is broadly there — because chemistry marks are lost in execution and precision far more often than in content ignorance. If the content genuinely is not there, fix that first, but check rather than assume.
When should we start for O-Levels? Sec 3, if moles were difficult. Moles underpin most of the quantitative work that follows, and a shaky start there compounds through both years.
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