AP Chemistry Practice Test 9
60 original exam-style multiple-choice questions with answers & explanations — covering all nine units of the AP Chemistry course.
Note: These are original practice questions written in the AP Chemistry exam style — not reproduced College Board questions. Use them to test your readiness for the real AP Chemistry exam.
📱 How to use: Try each question first, then click “Show Answer” to check. Covers all 9 AP units: atomic structure, compound structure, intermolecular forces, reactions, kinetics, thermodynamics, equilibrium, acids & bases, and applications of thermodynamics.
⚛ Unit 1: Atomic Structure & Properties
Q1What is the ground-state electron configuration of a chromium atom, Cr (Z = 24)?
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Correct: (B)
Chromium is an exception to the usual filling order; a half-filled 3d subshell gives [Ar] 4s1 3d5.
Q2The photoelectron spectrum of an element shows five peaks, in order of decreasing binding energy, with relative heights 2, 2, 6, 2, and 3. What is the element?
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Correct: (C)
The peak heights sum to 2 + 2 + 6 + 2 + 3 = 15 electrons, which is phosphorus.
Q3Which of the following atoms has the largest atomic radius?
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Correct: (A)
K is farthest to the left in period 4, so its valence electron is least tightly held and its radius is largest.
Q4An element consists of two isotopes: one with mass 62.9296 amu and percent abundance 69.17%, and one with mass 64.9278 amu and percent abundance 30.83%. What is the average atomic mass of the element?
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Correct: (D)
(0.6917 × 62.9296) + (0.3083 × 64.9278) = 43.53 + 20.02 = 63.55 amu.
Q5What is the ground-state electron configuration of an Fe^2+ ion (Fe, Z = 26)?
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Correct: (B)
Fe^2+ forms by removing the two 4s electrons first, leaving [Ar] 3d6.
Q6An element shows a very large increase between its third and fourth successive ionization energies. In which group is the element most likely found?
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Correct: (D)
The large jump after the third electron is removed means the atom has three valence electrons, placing it in group 13.
Q7What is the energy of a photon of light with frequency 6.00 × 10^14 s^-1? (Planck constant h = 6.626 × 10^-34 J s)
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Correct: (C)
E = h nu = (6.626 × 10^-34)(6.00 × 10^14) = 3.98 × 10^-19 J.
🔗 Unit 2: Molecular & Ionic Compound Structure
Q8In the best Lewis structure of the nitrate ion, NO3^-, what is the formal charge on the nitrogen atom?
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Correct: (A)
Nitrogen has no lone pairs and four bonds, so formal charge = 5 – 0 – 4 = +1.
Q9Which of the following species is best described by resonance structures?
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Correct: (C)
The carbonate ion has three equivalent structures with the double bond in a different position in each.
Q10What is the molecular geometry of SF4?
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Correct: (B)
SF4 has five electron domains (four bonds and one lone pair), giving a seesaw molecular geometry.
Q11In ethene, C2H4, what is the hybridization of each carbon atom, and how many pi bonds are in the molecule?
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Correct: (D)
Each carbon has three electron domains (sp2), and the C=C double bond contains one sigma and one pi bond.
Q12Which ionic compound has the lattice energy with the greatest magnitude?
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Correct: (A)
MgO combines +2 and -2 charges with small ionic radii, giving the strongest ionic attractions.
Q13Which of the following bonds is the most polar?
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Correct: (C)
Fluorine has the largest electronegativity, so the H-F bond has the greatest electronegativity difference.
Q14What is the approximate bond angle in an NH3 molecule?
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Correct: (B)
The lone pair on nitrogen compresses the H-N-H angles from 109.5° to about 107°.
💧 Unit 3: Intermolecular Forces & Properties
Q15Which of the following substances has the highest boiling point?
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Correct: (D)
Methanol molecules form hydrogen bonds, which require the most energy to overcome.
Q16Which of the following substances is most soluble in water?
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Correct: (A)
Ethanol is polar and hydrogen bonds with water, while the other choices are nonpolar.
Q17How much energy is required to vaporize 18.0 g of water at its boiling point? (ΔHvap of water = 40.7 kJ/mol, molar mass of H2O = 18.0 g/mol)
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Correct: (B)
18.0 g is 1.00 mol of water, so the energy required is 1.00 × 40.7 = 40.7 kJ.
Q18Which of the following is a network covalent solid?
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Correct: (C)
Silicon dioxide consists of silicon and oxygen atoms joined by covalent bonds in a continuous three-dimensional network.
Q19What is the strongest type of intermolecular force present between HCl molecules in liquid HCl?
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Correct: (A)
HCl is a polar molecule without H bonded to N, O, or F, so dipole-dipole forces are its strongest intermolecular force.
Q20Which change will increase the solubility of a gas in water?
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Correct: (D)
Gases are more soluble at lower temperatures and at higher partial pressures of the gas above the liquid.
⚖ Unit 4: Chemical Reactions
Q21When the equation C3H8 + O2 → CO2 + H2O is balanced with the smallest whole-number coefficients, what is the coefficient of O2?
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Correct: (C)
The balanced equation is C3H8 + 5 O2 → 3 CO2 + 4 H2O.
Q22What is the oxidation number of sulfur in H2SO4?
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Correct: (B)
With H at +1 and O at -2, 2(+1) + S + 4(-2) = 0 gives S = +6.
Q23Solutions of BaCl2(aq) and Na2SO4(aq) are mixed and a precipitate forms. What is the net ionic equation for the reaction?
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Correct: (A)
BaSO4 is the insoluble product, and Na^+ and Cl^- are spectator ions omitted from the net ionic equation.
Q24For the reaction N2 + 3 H2 → 2 NH3, how many grams of NH3 are produced when 6.0 mol of H2 reacts completely with excess N2? (Molar mass of NH3 = 17 g/mol)
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Correct: (D)
6.0 mol H2 × (2 mol NH3 / 3 mol H2) = 4.0 mol NH3, and 4.0 × 17 = 68 g.
Q25For the reaction 2 Al + 3 Cl2 → 2 AlCl3, a mixture contains 4.0 mol of Al and 5.0 mol of Cl2. Which reactant is the limiting reactant?
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Correct: (B)
4.0 mol of Al would require 6.0 mol of Cl2, but only 5.0 mol is available, so Cl2 is limiting.
Q26A reaction has a theoretical yield of 20.0 g of product, but only 15.0 g is actually obtained. What is the percent yield?
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Correct: (C)
Percent yield = (15.0 / 20.0) × 100% = 75%.
Q27A 25.00 mL sample of HCl(aq) is titrated to the endpoint with 20.00 mL of 0.100 M NaOH(aq). What is the concentration of the HCl?
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Correct: (A)
Moles of NaOH = 0.100 × 0.02000 = 0.00200 mol, equal to the moles of HCl, so [HCl] = 0.00200 / 0.02500 = 0.0800 M.
⏱ Unit 5: Kinetics
Q28For a reaction, the following data were collected: Experiment 1, [A] = 0.10 M, [B] = 0.10 M, rate = 0.020 M/s; Experiment 2, [A] = 0.20 M, [B] = 0.10 M, rate = 0.080 M/s; Experiment 3, [A] = 0.10 M, [B] = 0.20 M, rate = 0.020 M/s. What is the rate law?
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Correct: (D)
Doubling [A] quadruples the rate (second order in A), while doubling [B] has no effect (zero order in B).
Q29A first-order reaction has a rate constant k = 0.0231 min^-1. What is the half-life of the reaction?
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Correct: (B)
t1/2 = 0.693 / k = 0.693 / 0.0231 = 30 min.
Q30The concentration of a reactant decreases from 0.80 M to 0.40 M during the first 20 s of a reaction. What is the average rate of disappearance of the reactant during this interval?
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Correct: (C)
Average rate = (0.80 – 0.40) / 20 = 0.40 / 20 = 0.020 M/s.
Q31A proposed mechanism for the decomposition of NO2Cl is shown below. Step 1: NO2Cl → NO2 + Cl (slow) Step 2: NO2Cl + Cl → NO2 + Cl2 (fast). What is the rate law predicted by this mechanism?
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Correct: (B)
The rate is determined by the slow step, Step 1, which involves one molecule of NO2Cl, so the rate law is first order in NO2Cl only.
Q32According to collision theory, which factor best explains why a small increase in temperature often causes a large increase in reaction rate?
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Correct: (C)
Raising temperature shifts the energy distribution so a substantially larger fraction of molecular collisions exceed the activation energy barrier.
Q33A reaction has a rate constant that triples when the temperature is increased from 300 K to 310 K. Using ln(k2/k1) = (Ea/R)(1/T1 − 1/T2) with R = 8.314 J/mol·K, the activation energy is closest to
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Correct: (A)
ln(3) = 1.099 = (Ea/8.314)(1/300 − 1/310) = (Ea/8.314)(1.075 × 10^-4), giving Ea ≈ 85,000 J/mol or 85 kJ/mol.
Q34How does a heterogeneous catalyst increase the rate of a gas-phase reaction?
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Correct: (D)
Reactants adsorb on the catalyst surface, which weakens bonds and provides a different mechanism with a lower activation energy; the catalyst is regenerated.
🔥 Unit 6: Thermodynamics
Q35When a fuel sample is burned in a calorimeter, 100. g of water increases in temperature from 25.0°C to 31.5°C. The specific heat of water is 4.184 J/g°C. The heat released by the combustion, q, is closest to
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Correct: (C)
q(water) = mcΔT = (100.)(4.184)(6.5) = 2,720 J = 2.72 kJ absorbed by water, so the combustion released 2.72 kJ.
Q36Given: C(s) + O2(g) → CO2(g), ΔH = −393.5 kJ/mol and CO(g) + 1/2 O2(g) → CO2(g), ΔH = −283.0 kJ/mol. What is ΔH for C(s) + 1/2 O2(g) → CO(g)?
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Correct: (B)
By Hess's law, reverse the second reaction and add it to the first: −393.5 + 283.0 = −110.5 kJ/mol.
Q37Use bond enthalpies: H−H = 436 kJ/mol, Cl−Cl = 243 kJ/mol, H−Cl = 431 kJ/mol. Estimate ΔH for H2(g) + Cl2(g) → 2 HCl(g).
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Correct: (D)
ΔH = bonds broken − bonds formed = (436 + 243) − 2(431) = 679 − 862 = −183 kJ/mol.
Q38Standard heats of formation are: CH4(g) = −74.8 kJ/mol, CO2(g) = −393.5 kJ/mol, H2O(l) = −285.8 kJ/mol, O2(g) = 0 kJ/mol. What is ΔH° for CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(l)?
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Correct: (A)
ΔH° = [−393.5 + 2(−285.8)] − [−74.8 + 0] = −965.1 + 74.8 = −890.3 kJ/mol.
Q39In which process does the entropy of the system increase?
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Correct: (B)
Sublimation converts an ordered solid to a gas with much greater dispersal of matter and energy, so entropy increases; condensation, freezing, and compression all decrease entropy.
Q40A 50.0 g metal sample at 100.0°C is placed in 100. g of water at 20.0°C. The final temperature is 24.0°C. The specific heat of water is 4.184 J/g°C. Assuming no heat loss, the specific heat of the metal is closest to
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Correct: (D)
Heat gained by water = (100.)(4.184)(4.0) = 1,674 J. For the metal, c = 1,674 / [(50.0)(76.0)] = 0.44 J/g°C.
Q41Which reaction represents the standard heat of formation of liquid ethanol, C2H5OH(l)?
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Correct: (C)
A formation reaction forms one mole of compound from its elements in their standard states: graphite for carbon, H2(g), and O2(g).
⇆ Unit 7: Equilibrium
Q42What is the correct Kc expression for 2 SO2(g) + O2(g) ⇌ 2 SO3(g)?
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Correct: (A)
Kc is products raised to their coefficients divided by reactants raised to their coefficients.
Q43For N2O4(g) ⇌ 2 NO2(g) at 298 K, Kc = 0.50. What is Kp? Use Kp = Kc(RT)^Δn with R = 0.08206 L·atm/mol·K.
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Correct: (D)
Δn = 2 − 1 = 1, so Kp = 0.50 × (0.08206 × 298) = 0.50 × 24.5 = 12.
Q44For A(g) ⇌ B(g), Kc = 4.0. If the initial concentration of A is 1.0 M and B is initially 0 M, what is the equilibrium concentration of B?
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Correct: (B)
Let x = [B] at equilibrium, then [A] = 1.0 − x and Kc = x/(1.0 − x) = 4.0, giving x = 0.80 M.
Q45For a reaction at equilibrium conditions where the reaction quotient Q is calculated to be greater than K, what will happen as the system reaches equilibrium?
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Correct: (C)
If Q greater than K, there is too much product relative to equilibrium, so the net reaction shifts left toward reactants.
Q46For the exothermic reaction N2(g) + 3 H2(g) ⇌ 2 NH3(g), ΔH less than 0, how will increasing the temperature affect the equilibrium and K?
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Correct: (B)
Heat can be treated as a product in an exothermic reaction; adding heat shifts equilibrium left, and K decreases for an exothermic reaction as temperature rises.
Q47The Ksp of AgCl is 1.8 × 10^-10 at 25°C. What is the molar solubility of AgCl in pure water?
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Correct: (A)
For AgCl, Ksp = s^2, so s = square root of 1.8 × 10^-10 = 1.3 × 10^-5 M.
Q48The Ksp of CaF2 is 3.9 × 10^-11. What is the approximate molar solubility of CaF2 in 0.10 M NaF?
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Correct: (D)
With common ion [F^-] ≈ 0.10 M, Ksp = s(0.10)^2 = 0.010s, so s = 3.9 × 10^-11 / 0.010 = 3.9 × 10^-9 M.
🧫 Unit 8: Acids & Bases
Q49What is the pH of a 0.025 M HCl solution?
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Correct: (C)
HCl is a strong acid, so [H^+] = 0.025 M and pH = −log(0.025) = 1.60.
Q50A 0.10 M solution of a weak acid HA has a pH of 2.87. What is Ka for HA?
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Correct: (A)
[H^+] = 10^-2.87 = 1.35 × 10^-3 M. Ka = (1.35 × 10^-3)^2 / (0.10 − 0.00135) ≈ 1.8 × 10^-5.
Q51A buffer contains 0.20 M acetic acid (Ka = 1.8 × 10^-5, pKa = 4.74) and 0.30 M sodium acetate. What is the pH of the buffer?
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Correct: (D)
pH = pKa + log([base]/[acid]) = 4.74 + log(0.30/0.20) = 4.74 + 0.18 = 4.92.
Q52At the equivalence point of a titration of a weak acid with a strong base, the pH is greater than 7.0 because
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Correct: (B)
At equivalence the weak acid is converted to its conjugate base, which hydrolyzes: A^- + H2O ⇌ HA + OH^-, making the solution basic.
Q53Which pair is a conjugate acid-base pair?
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Correct: (C)
H2PO4^- and HPO4^2- differ by one proton: H2PO4^- can lose H^+ to form HPO4^2-, so they are a conjugate pair.
Q54For a diprotic acid H2A, Ka1 is much larger than Ka2. Which statement is correct?
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Correct: (A)
Removing a positive proton from HA^- is electrostatically harder than removing it from neutral H2A, so Ka2 is smaller than Ka1.
🔋 Unit 9: Applications of Thermodynamics
Q55A reaction has ΔH = −40. kJ/mol and ΔS = −100. J/mol·K. What is ΔG at 298 K, and is the reaction spontaneous?
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Correct: (D)
ΔG = ΔH − TΔS = −40. − (298)(−0.100) = −40. + 29.8 = −10.2 kJ/mol, so the reaction is spontaneous.
Q56A reaction has ΔH less than 0 and ΔS less than 0. Under what conditions is it spontaneous?
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Correct: (B)
With both ΔH and ΔS negative, ΔG = ΔH − TΔS is negative only when T is low enough that the favorable enthalpy term dominates.
Q57Standard reduction potentials: Cu^2+ + 2 e^- → Cu, E° = +0.34 V; Zn^2+ + 2 e^- → Zn, E° = −0.76 V. What is E°cell for the galvanic cell Zn(s) + Cu^2+ → Zn^2+ + Cu(s)?
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Correct: (C)
Zn is oxidized (anode) and Cu^2+ is reduced (cathode). E°cell = 0.34 − (−0.76) = +1.10 V.
Q58How many grams of Cu are deposited when a current of 2.00 A is passed for 9,650 s through a CuSO4 solution? Cu^2+ + 2 e^- → Cu, F = 96,500 C/mol e^-, molar mass of Cu = 63.55 g/mol.
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Correct: (A)
Charge = (2.00)(9,650) = 19,300 C = 0.200 mol e^-. Moles Cu = 0.200/2 = 0.100 mol, mass = 0.100 × 63.55 = 6.36 g.
Q59A reaction has ΔH = +100. kJ/mol and ΔS = +250. J/mol·K. At what temperature does the reaction become spontaneous, assuming ΔH and ΔS are constant?
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Correct: (D)
At the crossover, ΔG = 0, so T = ΔH/ΔS = 100,000 / 250 = 400 K. Above 400 K, the TΔS term dominates and ΔG is negative.
Q60For a galvanic cell with E°cell = +1.10 V and n = 2 mol of electrons transferred, what are the signs of ΔG° and the value of K relative to 1?
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Correct: (B)
ΔG° = −nFE°cell. With positive E°cell, ΔG° is negative, and a negative ΔG° corresponds to K greater than 1.
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