AP Chemistry Practice Test 13
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
Q1Which element has the ground-state electron configuration [Ar] 4s^2 3d^7?
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Correct: (B)
The configuration contains 18 + 2 + 7 = 27 electrons, which is the atomic number of cobalt.
Q2A photoelectron spectrum of an element shows three peaks with relative areas 2, 2, and 3 at binding energies of 40.6, 2.5, and 1.4 MJ/mol, respectively. The element is
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Correct: (A)
The peak areas give the configuration 1s^2 2s^2 2p^3, a total of 7 electrons, which is nitrogen.
Q3Which of the following elements has the highest first ionization energy?
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Correct: (D)
Ionization energy generally increases across a period; Si is farthest right and, despite the small Mg/Al exception, Si (787 kJ/mol) has the highest first ionization energy.
Q4An element consists of two isotopes: one with mass 62.93 amu and 69.2 percent abundance, and one with mass 64.93 amu and 30.8 percent abundance. The average atomic mass of the element is closest to
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Correct: (D)
(62.93)(0.692) + (64.93)(0.308) = 43.55 + 20.00 = 63.55 amu, closest to 63.5 amu (the element is copper).
Q5A sample contains 3.01 × 10^23 molecules of CO2. What is the mass of the sample?
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Correct: (B)
3.01 × 10^23 / 6.02 × 10^23 = 0.500 mol; 0.500 mol × 44.0 g/mol = 22.0 g.
Q6The ions Na+, Mg^2+, Al^3+, and F- are all isoelectronic. Which ion has the largest radius?
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Correct: (D)
For isoelectronic species, the ion with the fewest protons (F-, 9 protons) holds its electrons least tightly and is the largest.
Q7What is the electron configuration of Fe^3+?
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Correct: (B)
Transition metals lose their 4s electrons before 3d electrons, so Fe ([Ar] 4s^2 3d^6) loses three electrons to give [Ar] 3d^5.
🔗 Unit 2: Molecular & Ionic Compound Structure
Q8In the most stable Lewis structure of CO3^2-, the formal charge on the oxygen atom that is double-bonded to carbon is
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Correct: (A)
Formal charge = 6 − (4 nonbonding electrons + 2 bonding electrons) = 0.
Q9What is the molecular geometry of SF4?
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Correct: (D)
SF4 has five electron domains including one lone pair, which gives a seesaw molecular geometry.
Q10What is the hybridization of the nitrogen atom in NH3?
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Correct: (C)
Nitrogen in NH3 has four electron domains (three bonds and one lone pair), which requires sp^3 hybridization.
Q11Which compound has the greatest lattice energy?
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Correct: (A)
Lattice energy increases with ion charge and decreases with ion size; MgO combines 2+ and 2− charges with the smallest ions.
Q12What is the bond order of the bond in the N2 molecule?
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Correct: (C)
N2 contains a triple bond (one sigma bond and two pi bonds), so the bond order is 3.
Q13Which of the following species has resonance structures?
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Correct: (A)
SO3 can be drawn with the double bond to any one of the three equivalent oxygen atoms, giving three resonance structures.
Q14How many sigma bonds and pi bonds are in a molecule of acetonitrile, CH3-C≡N?
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Correct: (B)
There are five sigma bonds (three C-H, one C-C, one C-N) and two pi bonds in the C≡N triple bond.
💧 Unit 3: Intermolecular Forces & Properties
Q15Which of the following substances has the highest boiling point?
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Correct: (C)
Water forms the most extensive hydrogen-bonding network of these substances, giving it the highest boiling point (100°C).
Q16Which of the following substances is most soluble in water?
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Correct: (B)
Ethanol is polar and hydrogen bonds with water, so it is fully miscible; the other substances are nonpolar.
Q17How much energy is required to vaporize 18.0 g of water at 100°C? (ΔHvap = 40.7 kJ/mol)
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Correct: (D)
18.0 g / 18.0 g/mol = 1.00 mol; 1.00 mol × 40.7 kJ/mol = 40.7 kJ.
Q18Which of the following molecules experiences the weakest intermolecular forces in the liquid state?
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Correct: (C)
CH4 is nonpolar and experiences only weak London dispersion forces; the others are polar and hydrogen bond.
Q19Quartz (SiO2) is best classified as which type of solid?
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Correct: (D)
SiO2 consists of silicon and oxygen atoms linked in a continuous three-dimensional covalent network.
Q20What is the molarity of a solution prepared by dissolving 0.500 mol of NaCl in enough water to make 250.0 mL of solution?
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Correct: (A)
Molarity = 0.500 mol / 0.2500 L = 2.00 M.
⚖ Unit 4: Chemical Reactions
Q21When the equation C3H8(g) + O2(g) → CO2(g) + H2O(g) is balanced with the smallest whole-number coefficients, the coefficient of O2 is
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Correct: (C)
The balanced equation is C3H8 + 5 O2 → 3 CO2 + 4 H2O.
Q22Solutions of BaCl2(aq) and Na2SO4(aq) are mixed. Which equation is the net ionic equation for the reaction that occurs?
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Correct: (D)
BaSO4 precipitates; Na+ and Cl- are spectator ions and do not appear in the net ionic equation.
Q23What is the oxidation number of sulfur in H2SO4?
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Correct: (C)
2(+1) + S + 4(−2) = 0, so S = +6.
Q24What mass of CO2 is produced by the complete combustion of 11.0 g of C3H8 (molar mass 44.1 g/mol)?
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Correct: (A)
11.0 g / 44.1 g/mol = 0.249 mol C3H8; 0.249 × 3 = 0.748 mol CO2; 0.748 × 44.0 g/mol = 32.9 g.
Q25A mixture contains 4.0 mol of H2 and 1.5 mol of O2, which react according to 2 H2 + O2 → 2 H2O. How many moles of H2O can form?
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Correct: (B)
O2 is the limiting reactant (1.5 mol O2 needs only 3.0 mol H2, and 4.0 mol is available), so 1.5 mol O2 produces 3.0 mol H2O.
Q26A reaction has a theoretical yield of 50.0 g, but only 42.5 g of product is collected. The percent yield is
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Correct: (A)
Percent yield = (42.5 g / 50.0 g) × 100 = 85.0%.
Q27A 25.00 mL sample of HCl(aq) is exactly neutralized by 30.00 mL of 0.150 M NaOH(aq). What is the molarity of the HCl?
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Correct: (D)
Moles of NaOH = 0.03000 L × 0.150 M = 0.00450 mol, which equals the moles of HCl; 0.00450 mol / 0.02500 L = 0.180 M.
⏱ Unit 5: Kinetics
Q28Rate data for the reaction A + B → products are: Experiment 1: [A] = 0.10 M, [B] = 0.10 M, rate = 2.0 × 10^-3 M/s; Experiment 2: [A] = 0.20 M, [B] = 0.10 M, rate = 8.0 × 10^-3 M/s; Experiment 3: [A] = 0.10 M, [B] = 0.20 M, rate = 4.0 × 10^-3 M/s. The rate law for the reaction is
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Correct: (A)
Doubling [A] quadruples the rate (second order in A) and doubling [B] doubles the rate (first order in B).
Q29For a reaction that is second order overall, the units of the rate constant k are
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Correct: (C)
For overall order n, k has units of M^(1-n) s^-1; for n = 2 the units are M^-1 s^-1.
Q30The decomposition of a substance is first order with k = 0.0693 s^-1. The half-life of the substance is
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Correct: (B)
t1/2 = 0.693 / k = 0.693 / 0.0693 s^-1 = 10.0 s.
Q31A first-order reaction has k = 0.0231 min^-1. How long will it take for the concentration of reactant to decrease from 0.800 M to 0.200 M?
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Correct: (A)
t = ln(0.800 / 0.200) / k = ln(4) / 0.0231 = 1.386 / 0.0231 = 60.0 min.
Q32A proposed mechanism for the reaction NO2(g) + CO(g) → NO(g) + CO2(g) is: Step 1 (slow): 2 NO2 → NO3 + NO; Step 2 (fast): NO3 + CO → NO2 + CO2. The rate law predicted by this mechanism is
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Correct: (D)
The rate law is determined by the slow (rate-determining) step, which involves two NO2 molecules: Rate = k[NO2]^2.
Q33A catalyst increases the rate of a reaction by
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Correct: (C)
A catalyst provides a different mechanism with a lower activation energy, so a larger fraction of collisions lead to reaction.
Q34According to the Arrhenius equation, increasing the temperature increases the rate constant primarily because
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Correct: (D)
Raising the temperature shifts the distribution of molecular energies so that more collisions exceed the activation energy.
🔥 Unit 6: Thermodynamics
Q35How much heat is absorbed when 100.0 g of water is warmed from 25.0°C to 30.0°C? (specific heat of water = 4.18 J/g·°C)
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Correct: (D)
q = mcΔT = (100.0 g)(4.18 J/g·°C)(5.00°C) = 2090 J = 2.09 kJ.
Q36Given: C(s) + O2(g) → CO2(g), ΔH = −394 kJ; and CO(g) + 1/2 O2(g) → CO2(g), ΔH = −283 kJ. What is ΔH for C(s) + 1/2 O2(g) → CO(g)?
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Correct: (C)
By Hess's law, subtract the second reaction from the first: −394 − (−283) = −111 kJ.
Q37Using bond enthalpies (H−H = 436 kJ/mol, Cl−Cl = 242 kJ/mol, H−Cl = 431 kJ/mol), estimate ΔH for H2(g) + Cl2(g) → 2 HCl(g).
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Correct: (B)
ΔH = bonds broken − bonds formed = (436 + 242) − 2(431) = 678 − 862 = −184 kJ.
Q38Given ΔHf° values: CH4(g) = −75 kJ/mol, CO2(g) = −394 kJ/mol, H2O(l) = −286 kJ/mol. What is ΔH for CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(l)?
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Correct: (A)
ΔH = [−394 + 2(−286)] − [−75] = −966 + 75 = −891 kJ.
Q39For which of the following processes is ΔS positive?
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Correct: (C)
Sublimation converts a solid directly into a gas, which greatly increases the entropy.
Q40A 50.0 g sample of a metal at 100.0°C is placed in 100.0 g of water at 25.0°C, and the final temperature is 27.5°C. What is the specific heat of the metal? (specific heat of water = 4.18 J/g·°C)
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Correct: (B)
Heat gained by water = (100.0)(4.18)(2.5) = 1045 J; c(metal) = 1045 / [(50.0)(72.5)] = 0.288 J/g·°C.
Q41When 50.0 mL of 1.00 M HCl is mixed with 50.0 mL of 1.00 M NaOH in a calorimeter, the temperature of the resulting 100.0 g of solution rises by 6.8°C (specific heat = 4.18 J/g·°C). The enthalpy of neutralization is approximately
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Correct: (A)
q = (100.0 g)(4.18)(6.8) = 2840 J released by 0.0500 mol of reaction, so ΔH ≈ −2840 / 0.0500 = −57 kJ/mol.
⇆ Unit 7: Equilibrium
Q42For the equilibrium N2(g) + 3 H2(g) ⇌ 2 NH3(g), the equilibrium constant expression Kc is
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Correct: (B)
Products are placed over reactants, each concentration raised to its stoichiometric coefficient: [NH3]^2 / ([N2][H2]^3).
Q43For the reaction 2 SO2(g) + O2(g) ⇌ 2 SO3(g), Kc = 2.8 × 10^2 at 1000 K. What is Kp at 1000 K? (R = 0.0821 L·atm/mol·K)
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Correct: (A)
Δn = 2 − 3 = −1, so Kp = Kc(RT)^-1 = 280 / (0.0821 × 1000) = 280 / 82.1 = 3.4.
Q44For H2(g) + I2(g) ⇌ 2 HI(g), Kc = 49. A flask initially contains 1.00 M H2 and 1.00 M I2 and no HI. What is [HI] at equilibrium?
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Correct: (C)
(2x)^2 / (1.00 − x)^2 = 49 gives 2x / (1.00 − x) = 7, so x = 0.78 and [HI] = 2x = 1.56 M.
Q45For the equilibrium N2O4(g) ⇌ 2 NO2(g), ΔH° = +57 kJ/mol. If the temperature of the system is increased, the equilibrium will
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Correct: (B)
The reaction is endothermic, so added heat shifts the equilibrium toward products, and Kc increases with temperature for an endothermic reaction.
Q46The Ksp of AgCl is 1.8 × 10^-10. What is the molar solubility of AgCl in pure water?
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Correct: (A)
For AgCl, Ksp = s^2, so s = sqrt(1.8 × 10^-10) = 1.3 × 10^-5 M.
Q47For the reaction A(g) ⇌ B(g), Kc = 0.50. A mixture contains [A] = 0.20 M and [B] = 0.40 M. Which statement is correct?
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Correct: (C)
Q = [B] / [A] = 0.40 / 0.20 = 2.0, which is greater than Kc, so the reaction shifts left (toward A).
Q48Compared with its solubility in pure water, the solubility of CaF2(s) in 0.10 M NaF(aq) will be
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Correct: (C)
The F- ion already present (the common ion) shifts CaF2(s) ⇌ Ca^2+(aq) + 2 F-(aq) to the left, decreasing the solubility.
🧫 Unit 8: Acids & Bases
Q49What is the pH of 0.010 M HCl(aq)?
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Correct: (B)
HCl is a strong acid, so [H+] = 0.010 M and pH = −log(0.010) = 2.00.
Q50What is the pH of 0.100 M HF(aq)? (Ka of HF = 6.8 × 10^-4)
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Correct: (D)
[H+] = sqrt(Ka × 0.100) = sqrt(6.8 × 10^-5) = 8.2 × 10^-3 M, so pH = 2.08.
Q51A buffer solution contains 0.20 M CH3COOH and 0.20 M NaCH3COO. What is the pH of the buffer? (pKa of CH3COOH = 4.74)
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Correct: (A)
pH = pKa + log([base]/[acid]) = 4.74 + log(0.20 / 0.20) = 4.74 + 0 = 4.74.
Q52The conjugate base of HCO3- is
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Correct: (C)
Removing a proton (H+) from HCO3- gives its conjugate base, CO3^2-.
Q53A 0.10 M solution of CH3COOH is titrated with 0.10 M NaOH. At the equivalence point, the pH of the solution will be
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Correct: (D)
At the equivalence point the solution contains CH3COO-, which hydrolyzes to produce OH-, so the solution is basic.
Q54What is the Kb of F-, the conjugate base of HF? (Ka of HF = 6.8 × 10^-4)
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Correct: (B)
Kb = Kw / Ka = 1.0 × 10^-14 / 6.8 × 10^-4 = 1.5 × 10^-11.
🔋 Unit 9: Applications of Thermodynamics
Q55A reaction has ΔH° = −100 kJ/mol and ΔS° = −200 J/mol·K. What is ΔG° at 298 K?
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Correct: (C)
ΔG = ΔH − TΔS = −100 − (298)(−0.200) = −100 + 59.6 = −40.4 kJ/mol.
Q56A reaction with ΔH < 0 and ΔS < 0 is spontaneous
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Correct: (D)
ΔG = ΔH − TΔS is negative only at low temperatures, when the unfavorable entropy term does not outweigh the favorable enthalpy term.
Q57A galvanic cell is constructed with a Zn electrode in Zn^2+(aq) and a Cu electrode in Cu^2+(aq). Given E°(Zn^2+/Zn) = −0.76 V and E°(Cu^2+/Cu) = +0.34 V, the standard cell potential is
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Correct: (A)
Zn is oxidized at the anode and Cu^2+ is reduced at the cathode: E°cell = 0.34 − (−0.76) = +1.10 V.
Q58A current of 2.00 A is passed through a solution containing Cu^2+ for 30.0 min. What mass of copper is deposited at the cathode? (Cu^2+ + 2 e- → Cu; molar mass of Cu = 63.55 g/mol; F = 96485 C/mol e-)
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Correct: (D)
Charge = (2.00 A)(1800 s) = 3600 C = 0.0373 mol e-; moles of Cu = 0.0373 / 2 = 0.0187 mol; mass = 0.0187 × 63.55 = 1.19 g.
Q59For a galvanic cell with E°cell = +1.10 V that involves the transfer of 2 mol of electrons, ΔG° is
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Correct: (A)
ΔG° = −nFE° = −(2)(96485)(1.10) = −212,000 J/mol = −212 kJ/mol.
Q60Which of the following reactions has ΔS > 0?
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Correct: (B)
A gas is produced from a solid reactant, so the disorder and entropy of the system increase.
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