Getting ready for the AP Chemistry exam? These 20 free practice questions cover the big ideas from every unit of the course, each with a clear explanation. Try each question on your own first, then tap Show answer to check your thinking.
The questions are written in the style of the multiple-choice section of the exam. Keep a calculator and a periodic table nearby, just as you would on test day. They’re a quick way to find out which units you’ve mastered and which ones need more review.
What the AP Chemistry exam covers
- Atomic Structure and Properties: moles, mass spectra, electron configurations, photoelectron spectroscopy and periodic trends
- Compound Structure and Properties: ionic and covalent bonding, Lewis structures, VSEPR shapes and polarity
- Properties of Substances and Mixtures: intermolecular forces, gas laws, solutions, separation methods and spectroscopy
- Chemical Reactions: balanced and net ionic equations, stoichiometry, titrations and redox
- Kinetics: rate laws, half-life, reaction mechanisms, activation energy and catalysts
- Thermochemistry: heat, calorimetry, phase changes, bond enthalpies and Hess’s law
- Equilibrium: equilibrium constants, Q versus K, ICE tables, Le Chatelier’s principle and solubility
- Acids and Bases: pH, weak acids and bases, buffers and titration curves
- Thermodynamics and Electrochemistry: entropy, Gibbs free energy, galvanic and electrolytic cells
How to use these questions
Work through the questions without notes, the way you would on test day. Keep track of the ones you miss, and note which unit each one comes from. Two or three misses in the same unit is a sign to review that unit before moving on.
Don’t just check whether you got the right letter. Read every explanation, even for questions you answered correctly. AP Chemistry questions often test whether you can explain what is happening at the level of atoms and molecules, not just whether you can plug numbers into an equation.
Practice questions
Question 1
A compound contains 40.0% carbon, 6.7% hydrogen and 53.3% oxygen by mass. What is its empirical formula?
A. CHO
B. CH2O
C. C2H4O
D. CH4O
Show answer
Answer: B. Assume a 100 g sample: 40.0 g C is 3.33 mol, 6.7 g H is 6.65 mol, and 53.3 g O is 3.33 mol. Dividing each by 3.33 gives a 1 : 2 : 1 ratio, so the empirical formula is CH2O. A common trap is using the mass percents directly as the mole ratio.
Question 2
How many sigma (σ) bonds and pi (π) bonds are in one molecule of HCN?
A. 2 sigma and 2 pi
B. 3 sigma and 1 pi
C. 1 sigma and 3 pi
D. 4 sigma and 0 pi
Show answer
Answer: A. HCN has a single bond between H and C and a triple bond between C and N. Every single bond is one sigma bond, and a triple bond is one sigma bond plus two pi bonds. That gives 2 sigma bonds and 2 pi bonds in total.
Question 3
A sample of an ideal gas occupies 12.3 L at 2.00 atm and 300. K. How many moles of gas are in the sample? (R = 0.0821 L·atm·mol−1·K−1)
A. 0.500 mol
B. 2.00 mol
C. 1.00 mol
D. 4.00 mol
Show answer
Answer: C. Rearrange PV = nRT to n = PV/RT. That gives n = (2.00 atm)(12.3 L) / (0.0821 × 300. K) = 24.6 / 24.6, which is about 1.00 mol.
Question 4
At room temperature, F2 is a gas, while I2 is a solid. Which statement best explains this difference?
A. I2 molecules are polar, and F2 molecules are nonpolar.
B. I2 forms hydrogen bonds, and F2 does not.
C. The covalent bond inside I2 is stronger than the bond inside F2.
D. I2 has a larger, more polarizable electron cloud, so its London dispersion forces are stronger.
Show answer
Answer: D. Both molecules are nonpolar, so the only attractions between them are London dispersion forces. Iodine has many more electrons in a larger, more easily distorted electron cloud, which makes its dispersion forces much stronger. The trap is choice C: melting and boiling depend on forces between molecules, not on the covalent bond inside each molecule.
Question 5
What volume of 0.200 M NaOH is needed to completely neutralize 20.0 mL of 0.150 M H2SO4?
A. 15.0 mL
B. 30.0 mL
C. 7.50 mL
D. 60.0 mL
Show answer
Answer: B. There are 0.0200 L × 0.150 M = 0.00300 mol H2SO4. Sulfuric acid gives two H+ ions, so it needs 2 × 0.00300 = 0.00600 mol NaOH. Then 0.00600 mol ÷ 0.200 M = 0.0300 L, or 30.0 mL. Choice A is the trap you fall into if you forget the 2 : 1 mole ratio.
Question 6
A first-order reaction has a half-life of 20 minutes. What fraction of the original reactant remains after 60 minutes?
A. 1/3
B. 1/6
C. 1/2
D. 1/8
Show answer
Answer: D. Sixty minutes is three half-lives. After each half-life, half of what was left remains: 1/2, then 1/4, then 1/8. For a first-order reaction the half-life stays constant, so this pattern holds no matter how much reactant you start with.
Question 7
Using the standard enthalpies of formation ΔH°f: CH4(g) = −75 kJ/mol, CO2(g) = −394 kJ/mol and H2O(l) = −286 kJ/mol, what is ΔH° for CH4(g) + 2O2(g) → CO2(g) + 2H2O(l)?
A. −891 kJ
B. −605 kJ
C. +891 kJ
D. −1041 kJ
Show answer
Answer: A. ΔH° equals the sum of ΔH°f of products minus the sum for reactants: [−394 + 2(−286)] − [−75 + 0] = −966 + 75 = −891 kJ. O2 is an element in its standard state, so its ΔH°f is zero. Choice B comes from forgetting the coefficient of 2 on water.
Question 8
For the reaction 2SO2(g) + O2(g) ⇌ 2SO3(g), ΔH is negative. Which change will increase the amount of SO3 present at equilibrium?
A. Increasing the temperature
B. Adding a catalyst
C. Decreasing the temperature
D. Increasing the volume of the container
Show answer
Answer: C. The forward reaction is exothermic, so you can treat heat as a product. Lowering the temperature removes heat, and the system shifts toward products to replace it, forming more SO3. A catalyst speeds up both directions equally and does not change the equilibrium amounts, and a larger volume shifts the reaction toward the side with more gas molecules, which is the reactant side.
Question 9
Which of the following mixtures, in roughly equal amounts, would make a buffer solution?
A. HCl and NaCl
B. HC2H3O2 and NaC2H3O2
C. NaOH and NaCl
D. HNO3 and KNO3
Show answer
Answer: B. A buffer needs a weak acid and its conjugate base (or a weak base and its conjugate acid). Acetic acid is a weak acid, and the acetate ion from sodium acetate is its conjugate base. HCl and HNO3 are strong acids, and their anions are too weak as bases to absorb added acid, so those mixtures do not buffer.
Question 10
A reaction has a positive ΔH° and a positive ΔS°. Under standard conditions, the reaction is thermodynamically favorable
A. at all temperatures
B. at no temperature
C. only at low temperatures
D. only at high temperatures
Show answer
Answer: D. Use ΔG° = ΔH° − TΔS°. A positive ΔH° works against the reaction, but the −TΔS° term is negative and grows as temperature rises. At a high enough temperature, the entropy term outweighs the enthalpy term and ΔG° becomes negative.
More practice from the AP+ workbook
These next 10 questions come straight from our AP+ Review Workbook, with the same explanations you’ll find in its answer key.
Question 11
The ions O2−, F−, Na+, and Mg2+ are isoelectronic. Which has the largest ionic radius?
A. Mg2+
B. F−
C. Na+
D. O2−
Show answer
Answer: D. All four ions have the same number of electrons. The ion with the fewest protons pulls on those electrons most weakly, so its electron cloud is the largest. Oxygen has only 8 protons, so O2− has the largest radius.
Question 12
Which compound is expected to have the greatest lattice energy?
A. NaF
B. NaCl
C. KBr
D. MgO
Show answer
Answer: D. Lattice energy depends on the charges of the ions and how close together they are. MgO combines 2+ and 2− charges with relatively small ions, which produces the strongest attraction. The other choices all contain only 1+ and 1− ions.
Question 13
Which pure liquid is expected to have the highest vapor pressure at 25°C?
A. H2O
B. CH3OH
C. C5H12
D. HOCH2CH2OH
Show answer
Answer: C. Vapor pressure is highest for the liquid with the weakest intermolecular forces. Pentane, C5H12, is nonpolar and has only dispersion forces, so it is the most volatile. The other three liquids all form hydrogen bonds.
Question 14
In MnO4− → Mn2+, manganese is
A. oxidized because its oxidation number increases
B. reduced because its oxidation number decreases
C. neither oxidized nor reduced
D. a spectator ion
Show answer
Answer: B. In MnO4−, manganese has an oxidation number of +7. In Mn2+ it is +2. A decrease in oxidation number means the atom gained electrons, so manganese is reduced.
Question 15
Initial-rate data: Trial 1, [A] = 0.100 M, [B] = 0.100 M, rate = 2.00×10−3 M/s; Trial 2, [A] = 0.200 M, [B] = 0.100 M, rate = 8.00×10−3 M/s; Trial 3, [A] = 0.200 M, [B] = 0.200 M, rate = 8.00×10−3 M/s.
If [A] is tripled while [B] remains constant, the rate changes by a factor of
A. 3
B. 6
C. 9
D. 27
Show answer
Answer: C. From the data, doubling [A] (Trials 1 and 2) quadruples the rate, so the reaction is second order in A. Changing [B] (Trials 2 and 3) does not change the rate, so it is zero order in B. With rate = k[A]2, tripling [A] multiplies the rate by 32 = 9.
Question 16
Using average bond enthalpies H–H = 436, Cl–Cl = 243, H–Cl = 431 kJ/mol, ΔH for H2 + Cl2 → 2HCl is closest to
A. −183 kJ
B. +183 kJ
C. −679 kJ
D. +862 kJ
Show answer
Answer: A. ΔH is approximately the energy of bonds broken minus the energy of bonds formed. Breaking one H–H and one Cl–Cl bond costs 436 + 243 = 679 kJ, and forming two H–Cl bonds releases 2(431) = 862 kJ. So ΔH ≈ 679 − 862 = −183 kJ.
Question 17
For Ag2CrO4(s) ⇌ 2Ag+(aq) + CrO42−(aq), Ksp is
A. [Ag+][CrO42−]
B. 2[Ag+][CrO42−]
C. [Ag+]2[CrO42−]
D. [Ag2CrO4]/([Ag+]2[CrO42−])
Show answer
Answer: C. Pure solids are left out of equilibrium expressions, so only the dissolved ions appear. Each concentration is raised to the power of its coefficient, and the coefficient of Ag+ is 2. That gives Ksp = [Ag+]2[CrO42−].
Question 18
The question refers to 25.00 mL of 0.100 M weak acid HA (Ka = 1.8×10−5) titrated with 0.100 M NaOH.
At the half-equivalence point, the pH is
A. 2.87
B. 4.74
C. 7.00
D. 9.26
Show answer
Answer: B. At the half-equivalence point, half of the HA has been converted to A−, so [HA] = [A−]. The Henderson–Hasselbalch equation then gives pH = pKa = −log(1.8×10−5) = 4.74.
Question 19
A reaction has ΔH° = −46.0 kJ/mol and ΔS° = −99.0 J·mol−1·K−1. At 500 K, ΔG° is closest to
A. +3.5 kJ/mol
B. −3.5 kJ/mol
C. −95.5 kJ/mol
D. +95.5 kJ/mol
Show answer
Answer: A. Convert ΔS° to kJ first: −0.0990 kJ·mol−1·K−1. Then ΔG° = ΔH° − TΔS° = −46.0 − (500)(−0.0990) = −46.0 + 49.5 = +3.5 kJ/mol. At this high temperature, the unfavorable entropy term wins.
Question 20
A 2.00 A current passes through CuSO4(aq) for 965 s. The mass of Cu deposited is closest to
A. 0.318 g
B. 0.636 g
C. 1.27 g
D. 6.36 g
Show answer
Answer: B. The charge is 2.00 A × 965 s = 1930 C, and 1930 C ÷ 96,485 C/mol = 0.0200 mol of electrons. Each Cu2+ ion needs 2 electrons, so 0.0100 mol Cu forms, which is 0.0100 × 63.55 g/mol ≈ 0.636 g.
How did you do?
If you got 17 or more right, you have a strong foundation. Focus your review on the explanations for any you missed. If you got 12 to 16 right, you’re on track, but a few units need more practice. If you got 11 or fewer right, start with the unit reviews before doing more practice questions.
Our AP+ Chemistry Review Workbook covers every unit with clear summaries, worked examples, lab and data practice and a full-length practice exam with answers and step-by-step explanations. It’s available as an instant PDF download or a paperback.
See the AP+ Chemistry Review Workbook →
Studying for more than one AP exam? Browse the full AP+ Exam Prep series.
Frequently asked questions
Are these questions like the real AP Chemistry exam?
They’re written in the style of the multiple-choice section and cover the same units and skills. Official practice materials from the College Board are also worth using alongside them.
What’s the best way to study for AP Chemistry?
Review one unit at a time, practice calculations until the setup feels automatic, and explain your answers in terms of particles and forces. Mixed practice from different units, plus reading every explanation, builds the understanding the exam rewards.
When is the AP Chemistry exam?
AP exams are given each May. Check the College Board’s AP website for the current exam schedule.
AP is a registered trademark of the College Board, which was not involved in the production of, and does not endorse, this page or our workbooks.