AP Chemistry: how to study for the exam (the nine units as procedures and vocabulary, the calculator discipline, the lab-based questions, and where SCH4U overlaps)

AP Chemistry tests nine units: atomic structure, bonding, intermolecular forces, reactions, kinetics, thermochemistry, equilibrium, acids and bases, and electrochemistry with thermodynamics. It asks about them in a multiple-choice section and a free-response section with long and short questions. About half the course is calculation procedures, which you learn by redoing worked problems. The other half is explanation at the level of particles, forces and energy, which you learn by recall and drawing. Here are the units sorted that way, the exam's shape, the calculator habits that save marks, and an eight-week plan. The general method behind it is the practice-test method and the error log; this page is the chemistry version.

The nine AP Chemistry units, in our words

The College Board organises the course into nine units. Here is what each one asks of you, in our words, with the approximate weighting the current course description gives each unit in the multiple-choice section. The ranges are the College Board's; check the current description before you plan by them, because they can change between editions.

1. Atomic structure and properties (about 7–9 %). Moles and molar mass, mass spectra, electron configuration, photoelectron spectra, periodic trends.
2. Compound structure and properties (about 7–9 %). Ionic, covalent and metallic bonding, Lewis structures, resonance and formal charge, molecular shape and polarity.
3. Properties of substances and mixtures (about 18–22 %). Intermolecular forces and what they do to melting points, boiling points and solubility; solids, liquids and gases; the gas laws; solutions and their concentrations; separation; spectroscopy and light.
4. Chemical reactions (about 7–9 %). Writing and balancing equations, net ionic equations, reaction types, stoichiometry and titration calculations.
5. Kinetics (about 7–9 %). Reaction rates, rate laws and order, half-life, the collision model, mechanisms and the rate-determining step, catalysts.
6. Thermochemistry (about 7–9 %). Heat and temperature at the particle level, calorimetry, enthalpy of reaction, Hess's law, bond enthalpies.
7. Equilibrium (about 7–9 %). The equilibrium constant, ICE tables, Le Chatelier's principle, solubility equilibria and Ksp.
8. Acids and bases (about 11–15 %). pH and pOH, strong and weak acids and bases, titration curves, buffers, acid–base properties of salts.
9. Applications of thermodynamics and electrochemistry (about 7–9 %). Entropy, Gibbs free energy and the direction of change, galvanic and electrolytic cells, cell potentials, Faraday's law.

Two things stand out when you read the list as a planner. Unit 3 alone is about a fifth of the multiple-choice section. Units 3 and 8 together are about a third. A student who spends the same week on every unit is spending too little on those two.

The AP Chem exam format in one table

The exam has two sections, each worth half of the score. The format below is the current one as the College Board describes it; confirm it on AP Central before exam day, because the delivery has changed more than once.

Section	What is in it	Time	Share of the score
I: Multiple choice	60 questions, some standing alone and some in sets built on shared data or a diagram	1 hour 30 minutes	50 %
II: Free response	7 questions: 3 long (10 points each) and 4 short (4 points each)	1 hour 45 minutes	50 %

A scientific or graphing calculator is recommended for both sections, which has been the case since the 2023 exam. You are given a periodic table and a sheet of equations and constants for the whole exam. The exam is delivered in a hybrid digital form: you read every question on screen, answer the multiple-choice questions on screen, and handwrite the free-response answers in a paper booklet. The two section scores combine into a composite that is converted to a score from 1 to 5.

Three consequences for how you study. First, the free-response section is handwritten under time, so practise writing set-ups by hand at the pace the suggested times imply, about 23 minutes for a long question and about 9 for a short one. Second, the equations sheet is provided, so read it now and stop memorising what is on it; spend that memory on what is not. Third, the multiple-choice sets built on shared data reward reading a table or a graph before reading the questions, and that is a skill you can practise.

Procedures or vocabulary: the units sorted the other way

The nine units are how the course is taught. They are not how you learn it. Every unit contains two kinds of thing, and each kind has its own method. This is the same sort the SCH4U course map uses for the Ontario course, applied to AP.

Procedures: calculations with a set-up. Stoichiometry and limiting reagent. The gas laws. Calorimetry and Hess's law. Rate laws, reaction order and half-life. Equilibrium constants and ICE tables. Ksp and molar solubility. pH, pOH and buffers. Titration curves and the equivalence point. Gibbs free energy from enthalpy and entropy. Cell potentials and Faraday's law. For each of these there is a set-up that is the same every time, with different numbers.

The method for a procedure is the worked example done cold. Sweller and Cooper (1985) found that students who studied worked examples and then solved matching problems learned algebra procedures faster, and did better on new problems, than students who only solved problems. The AP version: read one worked example slowly, cover it, redo it from the question alone on a blank page, mark it line by line, then do a sibling with new numbers. The worked-example cycle is the full method with the marking rule. Twenty minutes a procedure, and every procedure on the list above gets a turn.

Vocabulary and models: explanations at the particle level. Electron configuration and what a photoelectron spectrum shows. Periodic trends and why they run the way they do. Lewis structures and the shapes they predict, which is molecular geometry and bond angles, every shape. Intermolecular forces and their consequences for boiling point and solubility. Solution properties. Reaction types. Mechanisms and intermediates. Le Chatelier's principle in words. The definitions of acids and bases and what makes one strong. Thermodynamic reasoning in words: why a reaction is spontaneous, why entropy rises.

The method for a model is recall and drawing. Roediger and Karpicke (2006) showed that students who recalled a passage from memory remembered more of it a week later than students who reread it, even though the rereaders felt more confident. For AP, that means cards whose front asks a question and whose back is the explanation in the model's own terms, and blank-page drawings of molecules, ions and energy diagrams checked against the textbook. The chemistry-specific version is in how to study chemistry: the diagram redrawn, the trend explained, the definition said aloud.

One unit, two methods. Thermochemistry is calorimetry and Hess's law (procedures) and the particle picture of heat flowing from a hot block into cold water (model). Study both halves and the unit is covered. Study one and the free-response section finds the other.

The three kinds of question, and how each is marked

Free-response questions in AP Chemistry come in three shapes, and knowing which one you are looking at tells you what to write.

The calculation with a set-up. The scoring guidelines for a calculation give credit for the set-up as well as the answer: the equation chosen, the values substituted with their units, and the final answer with sensible significant figures. A right number from nowhere earns less than a right set-up with an arithmetic slip. So write the equation first, every time, even when you can do the arithmetic in your head.

The particulate explanation. A question that says "explain in terms of" wants the model named and used: intermolecular forces, equilibrium, energy, kinetics, or the structure of the atom. An answer that restates the observation ("it boils at a higher temperature because it is harder to boil") earns nothing. An answer that names the force ("hydrogen bonding between molecules of the first compound, which the second cannot form, so more energy is needed to separate them") earns the point. The habit to build: before you write, say which model the question lives in. Forces, equilibrium, energy, kinetics or structure. Then write in that model's words.

The particulate drawing. A diagram of molecules, ions or energy levels that shows the claim. A saturated solution drawn with the right ratio of ions. A reaction coordinate with the activation energy and the enthalpy change labelled. A beaker of a strong acid drawn with every molecule dissociated and a weak acid with most of them whole. The drawing is marked on whether it shows the chemistry, not on whether it is pretty.

The way to practise all three is the College Board's released free-response questions, which it publishes with the scoring guidelines that were used to mark them. Do a set under the real time, then grade yourself against the guideline line by line, not against your feeling about the answer. Nothing else trains the explanation and drawing questions as well, because nothing else shows you what earned the point and what did not.

The calculator discipline

The calculator is allowed throughout. The marks it loses are the ones you give away around it. Four habits.

1. Carry significant figures, do not round midway. Keep every digit in the calculator until the last line, then round once to the figures the data justify.
2. Units on every substituted value. A unit that does not cancel is the fastest way to find a wrong set-up before the marker does.
3. One line of sanity check. A pH of 14.6 for a weak acid, a molar solubility larger than the concentration you started with, a negative half-life: each is a flag that something upstream is wrong.
4. Read the equations sheet before the exam. Nothing on it needs memorising. What is not on it does.

Two worked examples, ours, both checkable.

Molar solubility from Ksp. Silver chloride has a solubility product of about 1.8 × 10⁻¹⁰ at 25 °C (a textbook value; tables differ in the last digit, so use the one your course gives). What is its molar solubility? The dissolution is AgCl(s) ⇌ Ag⁺(aq) + Cl⁻(aq), so each mole that dissolves gives one Ag⁺ and one Cl⁻. Call the solubility s. Then Ksp = [Ag⁺][Cl⁻] = s × s = s². So s = √(1.8 × 10⁻¹⁰). The square root of 1.8 is about 1.34, and the square root of 10⁻¹⁰ is 10⁻⁵, so s = 1.34 × 10⁻⁵ mol/L, which rounds to 1.3 × 10⁻⁵ mol/L because Ksp was given to two significant figures. Sanity check: a very small number, as a salt we call insoluble should give.

Two wrong lines a marker sees on this question: writing s = Ksp, the square root forgotten (that gives 1.8 × 10⁻¹⁰ mol/L, far too small); and, for a salt with two anions such as PbCl₂, writing Ksp = s² when the correct expression is s × (2s)² = 4s³. The error log entry for the first is "Ksp for a 1:1 salt is s², so take the root".

Heat from a temperature change. How much heat does 100.0 g of water absorb when it warms by 5.00 °C? The equation is q = mcΔT, with c = 4.18 J/g·°C for water. Substitute with units: q = 100.0 g × 4.18 J/g·°C × 5.00 °C. The grams cancel and the degrees cancel, leaving joules. The arithmetic: 100.0 × 4.18 = 418, and 418 × 5.00 = 2,090. So q = 2,090 J = 2.09 kJ, three significant figures because every value had at least three. Sanity check: a small warming of a glass of water should be a few kilojoules, and it is.

Two wrong lines: converting the mass to kilograms while keeping c in J/g·°C, which makes the answer a thousand times too small (the units did not cancel, which the second habit would have caught); and reporting 2,090 J as 2,090.0 J, which claims a fifth significant figure the data never had.

One more, for kinetics. A first-order reaction has a rate constant of 0.0231 s⁻¹. Its half-life is t½ = ln 2 / k = 0.693 / 0.0231 = 30.0 s. The check: ln 2 is on the equations sheet in the half-life formula, so you are reading it, not remembering it.

The lab-based questions

AP Chemistry's free-response set includes questions built on an experimental procedure. You are given a method a student followed and some data, and asked some combination of: what was measured, what was calculated from it, what a particular error would do to the result and in which direction, and what is wrong with the design or how it could be improved. The course framework names these as science practices: identifying a procedure that answers a question, identifying sources of error, predicting how a change to the procedure changes the result.

This is the part students from a course with less lab work, SCH4U included, find least familiar, and it is worth saying so. You can practise it without a lab bench. Take a released free-response question built on a procedure and, before you answer the parts, write three lines of your own: what quantity was measured directly, what quantity was calculated from the measurements and by which equation, and one thing that would push the result high and one that would push it low. Then answer the question and grade against the guideline. After ten of these the pattern is visible: a thermometer that reads low, a mass weighed with water still on it, a titration overshot by a drop. Each has a direction, and the direction follows from the equation.

Make one card per common error: front, "the beaker was wet before the solid was weighed; what happens to the calculated molar mass?"; back, the reasoning in two lines. That is recall practice on exactly the thing the question tests.

Where SCH4U overlaps

For Canadian readers taking AP after or beside Ontario's Grade 12 chemistry: SCH4U covers structure and bonding, intermolecular forces, kinetics, thermochemistry, equilibrium, acids and bases and electrochemistry, which is most of units 1 to 9. It spends a whole strand on organic chemistry, which AP does not test, and it asks for less particulate-level reasoning and less lab design than AP does. Here is the map, using our own SCH4U concept titles. There is no credit equivalence claimed between the two courses; this is a study map.

AP unit	SCH4U ideas that cover it	New to an SCH4U student
1 Atomic structure	Quantum mechanical model of the atom; electron configurations and periodic trends	Photoelectron spectroscopy; mass spectra read for isotopes
2 Compound structure	Ionic and covalent bonding, Lewis structures, electronegativity; molecular shape (VSEPR) and polarity	Formal charge used to choose between structures
3 Substances and mixtures	Intermolecular forces and physical properties; gas laws and stoichiometry	Spectroscopy and light; the depth of the solutions work
4 Reactions	Gas laws and stoichiometry; oxidation numbers and balancing redox reactions	Net ionic equations as the default
5 Kinetics	Reaction rates; rate laws and reaction order; activation energy, catalysts and mechanisms	Little: the same ideas at a similar depth
6 Thermochemistry	Enthalpy changes and calorimetry; Hess's law and enthalpies of formation	The particle picture of heat; bond enthalpies
7 Equilibrium	Dynamic equilibrium and the equilibrium constant; Le Chatelier's principle; solubility equilibria and Ksp	Little: the same ideas
8 Acids and bases	Acid–base theories, pH and strong/weak acids; buffers and titration	Titration curves read in detail; salts of weak acids and bases
9 Thermodynamics and electrochemistry	Galvanic cells and standard reduction potentials; electrolytic cells and Faraday's laws	Entropy and Gibbs free energy
(not on AP)	Organic functional groups, hydrocarbons, isomers, organic reactions, polymers

The three additions an SCH4U student should start with are photoelectron spectroscopy, Gibbs free energy, and the lab-based questions. Everything else is a depth adjustment, not a new idea.

The plan: eight weeks of AP chem review

An eight-week plan for a student with about an hour on most days. It is built from the two methods above and from the finding, in Rohrer and Taylor (2007), that practice problems shuffled across types produce better test performance a week later than the same problems done in blocks, because the shuffled set makes you choose the method, which is what the exam makes you do.

Week	What happens
1	One released exam under the real time, both sections. Grade it against the scoring guidelines. Log every miss by unit and by skill: procedure, explanation, drawing or lab.
2	Units 1 and 2: the procedures by the worked-example cycle, the models by cards and drawings. One released free-response set under time at the week's end.
3	Unit 3, the big one, for the whole week. From this week on, every problem set mixes units: mixed sets of eight, two from each unit studied so far. One free-response set under time.
4	Units 4 and 5. Mixed sets. One free-response set.
5	Units 6 and 7. Mixed sets now span six units. One free-response set.
6	Units 8 and 9, with extra time on unit 8. Mixed sets across all nine. One free-response set.
7	A second released exam under time. Compare the error log with week 1's. The three skills still missing most get the week.
8	The last week, compressed: a diagnostic, spaced sessions on the shaky list, a timed run, a light review, and sleep. The last week is the plan; chapter 9 of the free playbook is the same week on one page.

An "AP chemistry study guide", if you make one, is the unit list written as questions, one line each, not a summary of the textbook. A study guide written as questions shows how. A question you can answer with the notes closed is done; one you cannot is tonight's work. A summary tells you neither.

Practice tests are the hinge of the plan: one at the start, one near the end, and a free-response set every week between. A practice test is not a score. It is a list of the skills you have not yet got, sorted by unit.

AP Chemistry, on one screen

• Nine units. Unit 3 is about a fifth of the multiple-choice section and unit 8 about an eighth; weight the weeks accordingly.
• Two halves. Procedures by the worked-example cycle; models and vocabulary by recall cards and drawings.
• Three question kinds. The set-up calculation, the particulate explanation, the particulate drawing. Name the model before you write.
• The calculator discipline. Figures carried, units on every value, one sanity line, the equations sheet read in advance.
• The lab questions. Measured, calculated, and which way an error pushes.
• The plan. A released exam in week 1, two units a week by the two methods, mixed sets from week 3, a free-response set every week, a second exam in week 7, the compressed last week.