AP Chemistry Practice Test 17
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 an Fe^3+ ion?
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Correct: (B)
Iron is [Ar] 4s^2 3d^6; the 4s electrons are removed first, then one 3d electron, leaving 3d^5.
Q2A photoelectron spectrum of an unknown element shows five peaks, in order of decreasing binding energy, with relative heights 2, 2, 6, 2, and 2. Which element is it?
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Correct: (D)
The peak heights sum to 14 electrons and match 1s^2 2s^2 2p^6 3s^2 3p^2, the configuration of silicon.
Q3Which of the following period 3 elements has the highest first ionization energy?
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Correct: (A)
Ionization energy generally increases across a period as effective nuclear charge increases, and Si is farthest to the right in this set.
Q4A sample of magnesium consists of 79.0% Mg-24, 10.0% Mg-25, and 11.0% Mg-26. What is the average atomic mass of magnesium in this sample?
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Correct: (C)
(0.790 × 24) + (0.100 × 25) + (0.110 × 26) = 18.96 + 2.50 + 2.86 = 24.32 amu.
Q5How many unpaired electrons are in a ground-state chromium atom?
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Correct: (B)
Chromium is the exception [Ar] 4s^1 3d^5, so the single 4s electron and five 3d electrons are all unpaired, giving 6.
Q6The species S^2-, Cl-, K+, and Ca^2+ are isoelectronic. Which one has the largest radius?
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Correct: (D)
All have 18 electrons, but S^2- has the fewest protons, so the electrons are held least tightly and spread out most.
Q7Why is the second ionization energy of sodium so much larger than its first ionization energy?
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Correct: (A)
Na+ has a neon configuration; removing a second electron means taking it from the n = 2 shell, much closer to the nucleus.
🔗 Unit 2: Molecular & Ionic Compound Structure
Q8How many equivalent resonance structures can be drawn for the carbonate ion, CO3^2-, in which carbon obeys the octet rule?
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Correct: (C)
The double bond can be placed between carbon and any one of the three oxygen atoms, giving three equivalent structures.
Q9What is the formal charge on the nitrogen atom in the ammonium ion, NH4+?
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Correct: (A)
Formal charge = 5 valence electrons – (0 nonbonding + 4 bonding) = +1.
Q10What is the molecular geometry of SF4?
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Correct: (D)
Sulfur has five electron domains (four bonds and one lone pair) in a trigonal bipyramidal arrangement, giving a seesaw shape.
Q11What is the hybridization of each carbon atom in ethene, C2H4?
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Correct: (B)
Each carbon has three electron domains (two C-H bonds and one C=C bond region), which corresponds to sp^2 hybridization.
Q12Which ionic compound has the lattice energy with the greatest magnitude?
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Correct: (C)
MgO combines 2+ and 2- charges with small ions, giving the strongest attractions; CaS also has 2+/2- charges but larger ions.
Q13Which bond is the most polar?
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Correct: (A)
Fluorine is the most electronegative element, so the electronegativity difference with hydrogen is largest for H-F.
Q14In which molecule is the carbon-carbon bond the shortest?
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Correct: (D)
Ethyne has a carbon-carbon triple bond; bond length decreases as bond order increases, so the triple bond is shortest.
💧 Unit 3: Intermolecular Forces & Properties
Q15Which of the following pure liquids exhibits hydrogen bonding?
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Correct: (B)
NH3 has hydrogen atoms bonded directly to nitrogen, a small highly electronegative atom, so its molecules hydrogen bond.
Q16Which of the following hydrogen halides has the highest normal boiling point?
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Correct: (C)
None of these hydrogen bonds appreciably, and HI has the most electrons and the most polarizable electron cloud, so its London dispersion forces are strongest.
Q17A crystal of iodine, I2, will dissolve most readily in which solvent?
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Correct: (A)
I2 is nonpolar, and "like dissolves like" predicts it dissolves best in the nonpolar solvent CCl4.
Q18How much heat is required to raise the temperature of 50.0 g of liquid water from 25 C to 75 C? The specific heat of water is 4.18 J/g C.
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Correct: (D)
q = mcΔT = (50.0 g)(4.18 J/g C)(50 C) = 10,450 J, which is about 10.5 kJ.
Q19Diamond consists of carbon atoms each bonded covalently to four neighbors in a continuous three-dimensional array. Diamond is best classified as what type of solid?
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Correct: (B)
A continuous network of covalent bonds throughout the crystal defines a covalent network solid.
Q20What is the molarity of a solution prepared by dissolving 0.50 mol of NaCl in enough water to make 250. mL of solution?
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Correct: (C)
Molarity = 0.50 mol / 0.250 L = 2.0 M.
⚖ Unit 4: Chemical Reactions
Q21When the combustion equation C5H12 + O2 → CO2 + H2O is balanced with the smallest whole-number coefficients, what is the coefficient of O2?
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Correct: (A)
Pentane has 5 C and 12 H, giving 5 CO2 and 6 H2O, which contain 16 O atoms, so 8 O2 are required.
Q22In the reaction Sn^2+(aq) + 2 Fe^3+(aq) → Sn^4+(aq) + 2 Fe^2+(aq), which species is the reducing agent?
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Correct: (D)
Sn^2+ is oxidized from +2 to +4, losing electrons, so it reduces Fe^3+ and is the reducing agent.
Q23Aqueous solutions of Pb(NO3)2 and KI are mixed and a yellow solid forms. What is the net ionic equation for the reaction?
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Correct: (B)
PbI2 is insoluble; K^+ and NO3^- are spectator ions and are omitted from the net ionic equation.
Q24Ammonia is formed by N2(g) + 3 H2(g) → 2 NH3(g). If 6.0 mol of H2 reacts completely with excess N2, how many moles of NH3 are formed?
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Correct: (C)
6.0 mol H2 × (2 mol NH3 / 3 mol H2) = 4.0 mol NH3.
Q25A mixture contains 4.0 mol of Al and 4.5 mol of Cl2, which react by 2 Al(s) + 3 Cl2(g) → 2 AlCl3(s). Which reactant is limiting, and how many moles of AlCl3 can form?
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Correct: (A)
4.0 mol Al would require 6.0 mol Cl2, so Cl2 is limiting; 4.5 mol Cl2 × (2/3) = 3.0 mol AlCl3.
Q26A reaction has a theoretical yield of 25.0 g of product. If 20.0 g of product are actually isolated, what is the percent yield?
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Correct: (D)
Percent yield = (20.0 g / 25.0 g) × 100 = 80.0%.
Q27A 25.00 mL sample of HCl(aq) of unknown concentration is titrated to the endpoint with 20.00 mL of 0.200 M NaOH(aq). What is the concentration of the HCl?
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Correct: (B)
Moles NaOH = 0.200 M × 0.02000 L = 0.00400 mol = moles HCl; 0.00400 mol / 0.02500 L = 0.160 M.
⏱ Unit 5: Kinetics
Q28For the reaction A + B → products, 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 = 0.040 M/s; Experiment 3: [A] = 0.10 M, [B] = 0.20 M, rate = 0.080 M/s. What is the rate law?
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Correct: (C)
Doubling [A] doubles the rate (first order in A); doubling [B] quadruples the rate (second order in B).
Q29What are the units of the rate constant k for a reaction that is second order overall, when rate is measured in M/s and concentrations are in M?
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Correct: (A)
k = rate / [concentration]^2 = (M/s) / M^2 = M^-1 s^-1.
Q30A first-order reaction has a rate constant k = 0.0693 min^-1. What is the half-life of the reaction?
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Correct: (D)
t1/2 = ln 2 / k = 0.693 / 0.0693 min^-1 = 10.0 min.
Q31A proposed mechanism is: Step 1 (slow): A2(g) → 2 A(g); Step 2 (fast): A(g) + B(g) → AB(g). What rate law is predicted by this mechanism?
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Correct: (B)
The slow first step is rate-determining and involves only A2, so rate = k[A2].
Q32According to collision theory, why does raising the temperature increase the rate of most chemical reactions?
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Correct: (C)
Higher temperature shifts the energy distribution so a larger fraction of collisions can overcome the activation energy barrier.
Q33Which statement best describes how a catalyst affects a reaction at constant temperature?
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Correct: (A)
A catalyst lowers the activation energy by an alternative mechanism; reactant and product energies, and therefore ΔH, are unchanged.
Q34A first-order reaction starts with [R] = 0.80 M. After 40 s, [R] = 0.20 M. What is the half-life of the reaction?
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Correct: (D)
0.80 M → 0.40 M → 0.20 M is two half-lives in 40 s, so one half-life is 20 s.
🔥 Unit 6: Thermodynamics
Q35A reaction releases heat to its surroundings and the temperature of the surroundings rises. Which description is correct for the system?
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Correct: (B)
Heat released by the system is exothermic, and ΔH is negative for an exothermic reaction at constant pressure.
Q36Given: (1) C(s) + O2(g) → CO2(g), ΔH = −393 kJ/mol; (2) CO(g) + 1/2 O2(g) → CO2(g), ΔH = −283 kJ/mol. What is ΔH for C(s) + 1/2 O2(g) → CO(g)?
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Correct: (C)
By Hess's law, ΔH = −393 kJ/mol − (−283 kJ/mol) = −110 kJ/mol.
Q37How much heat is absorbed when 100. g of water is heated from 20.0°C to 30.0°C? The specific heat capacity of water is 4.184 J/(g·°C).
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Correct: (A)
q = mcΔT = 100. g × 4.184 J/(g·°C) × 10.0°C = 4184 J = 4.18 kJ.
Q38Using bond enthalpies H−H = 436 kJ/mol, Cl−Cl = 242 kJ/mol, and H−Cl = 431 kJ/mol, what is ΔH for H2(g) + Cl2(g) → 2 HCl(g)?
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Correct: (D)
ΔH = bonds broken − bonds formed = (436 + 242) − 2(431) = 678 − 862 = −184 kJ/mol.
Q39Which process is accompanied by an increase in the entropy of the system?
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Correct: (B)
Melting converts an ordered solid into a more disordered liquid, so ΔS > 0.
Q40Given standard enthalpies of formation: ΔHf of CH4(g) = −75 kJ/mol, CO2(g) = −394 kJ/mol, H2O(l) = −286 kJ/mol, and O2(g) = 0 kJ/mol. What is ΔH for CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(l)?
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Correct: (C)
ΔH = [−394 + 2(−286)] − [−75 + 0] = −966 + 75 = −891 kJ/mol.
Q41A reaction has ΔH < 0 and ΔS > 0. Which statement about its spontaneity is correct?
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Correct: (A)
ΔG = ΔH − TΔS is negative at all temperatures when ΔH is negative and ΔS is positive.
⇆ Unit 7: Equilibrium
Q42A flask initially contains 0.80 M N2O4(g). At equilibrium, the concentration of NO2(g) is 0.40 M for the reaction N2O4(g) ⇌ 2 NO2(g). What is the value of Kc at this temperature?
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Correct: (B)
Formation of 0.40 M NO2 consumes 0.20 M N2O4, leaving 0.60 M N2O4. Kc = (0.40)^2 / (0.60) = 0.27.
Q43For the reaction N2(g) + 3 H2(g) ⇌ 2 NH3(g), Kc = 1.50 × 10^2 at 500 K. What is the value of Kp at 500 K? (R = 0.0821 L·atm/mol·K)
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Correct: (D)
Δn = 2 – 4 = -2, so Kp = Kc(RT)^-2 = 150 / (0.0821 × 500)^2 = 150 / 1685 = 8.90 × 10^-2.
Q44For the reaction A(g) + B(g) ⇌ C(g), Kc = 10 at a certain temperature. In a mixture, [A] = 0.10 M, [B] = 0.10 M, and [C] = 0.50 M. Which statement correctly describes the mixture?
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Correct: (A)
Q = 0.50 / (0.10 × 0.10) = 50, which is greater than Kc = 10, so the net reaction shifts left toward reactants.
Q45The molar solubility of CaF2 in pure water is 2.0 × 10^-4 M. What is the Ksp of CaF2?
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Correct: (C)
For CaF2(s) ⇌ Ca^2+(aq) + 2 F^-(aq), Ksp = (s)(2s)^2 = 4s^3 = 4(2.0 × 10^-4)^3 = 3.2 × 10^-11.
Q46The Ksp of AgBr is 5.0 × 10^-13. What is the molar solubility of AgBr in 0.10 M NaBr(aq)?
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Correct: (B)
The common ion Br^- suppresses dissolution, so s = Ksp / [Br^-] = (5.0 × 10^-13) / 0.10 = 5.0 × 10^-12 M.
Q47PCl5(g) is placed in a container at an initial concentration of 0.20 M. For PCl5(g) ⇌ PCl3(g) + Cl2(g), Kc = 0.040. What is the equilibrium concentration of Cl2?
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Correct: (D)
Setting x^2 / (0.20 – x) = 0.040 gives x^2 + 0.040x – 0.0080 = 0, so x = 0.072 M, and [Cl2] = x.
Q48A solution is prepared in which [Ba^2+] = 1.0 × 10^-4 M and [SO4^2-] = 1.0 × 10^-3 M. The Ksp of BaSO4 is 1.1 × 10^-10. Which prediction is correct?
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Correct: (A)
Q = (1.0 × 10^-4)(1.0 × 10^-3) = 1.0 × 10^-7, which exceeds Ksp = 1.1 × 10^-10, so precipitation occurs.
🧫 Unit 8: Acids & Bases
Q49What is the pH of a 0.025 M HCl(aq) solution at 25°C?
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Correct: (C)
HCl is a strong acid, so [H^+] = 0.025 M and pH = -log(0.025) = 1.60.
Q50What is the pH of a 0.20 M solution of acetic acid, CH3COOH, at 25°C? (Ka = 1.8 × 10^-5)
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Correct: (B)
[H^+] = sqrt(Ka × C) = sqrt(1.8 × 10^-5 × 0.20) = 1.9 × 10^-3 M, so pH = 2.72.
Q51A buffer contains 0.30 M CH3COOH and 0.45 M CH3COO^-. The pKa of CH3COOH is 4.74. What is the pH of the buffer?
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Correct: (D)
pH = pKa + log([base]/[acid]) = 4.74 + log(0.45/0.30) = 4.74 + 0.18 = 4.92.
Q52A 25.0 mL sample of 0.10 M CH3COOH is titrated with 0.10 M NaOH. What is the pH at the equivalence point? (Ka for CH3COOH = 1.8 × 10^-5)
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Correct: (A)
At equivalence all the acid becomes 0.050 M CH3COO^-, which hydrolyzes with Kb = 1.0 × 10^-14 / 1.8 × 10^-5 = 5.6 × 10^-10. [OH^-] = sqrt(5.6 × 10^-10 × 0.050) = 5.3 × 10^-6 M, giving pOH = 5.28 and pH = 8.72.
Q53The Ka of NH4^+ is 5.6 × 10^-10 at 25°C. What is the Kb of its conjugate base, NH3, at 25°C?
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Correct: (C)
For a conjugate acid-base pair, Ka × Kb = Kw, so Kb = 1.0 × 10^-14 / 5.6 × 10^-10 = 1.8 × 10^-5.
Q54Carbonic acid, H2CO3, has Ka1 = 4.3 × 10^-7 and Ka2 = 5.6 × 10^-11. In a 0.10 M H2CO3 solution, the concentration of CO3^2- is closest to
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Correct: (B)
The first ionization produces nearly equal [H^+] and [HCO3^-], so in the second equilibrium Ka2 = [H^+][CO3^2-]/[HCO3^-] reduces to [CO3^2-] approx equal to Ka2 = 5.6 × 10^-11 M.
🔋 Unit 9: Applications of Thermodynamics
Q55A reaction has ΔH° = -120 kJ/mol and ΔS° = -150 J/mol·K. What is ΔG° for the reaction at 298 K?
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Correct: (D)
ΔG° = ΔH° – TΔS° = -120 kJ/mol – (298 K)(-0.150 kJ/mol·K) = -120 + 44.7 = -75 kJ/mol.
Q56A decomposition reaction has ΔH° = +80 kJ/mol and ΔS° = +200 J/mol·K. Under standard conditions, the reaction is spontaneous
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Correct: (A)
With ΔH and ΔS both positive, ΔG is negative only when TΔS exceeds ΔH. The crossover is T = 80,000 J/mol / 200 J/mol·K = 400 K, so the reaction is spontaneous above 400 K.
Q57A galvanic cell is constructed from the reaction Fe(s) + 2 Ag^+(aq) → Fe^2+(aq) + 2 Ag(s). Given E° for Ag^+/Ag is +0.80 V and E° for Fe^2+/Fe is -0.44 V, what is E°cell?
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Correct: (C)
Iron is oxidized (anode) and silver ion is reduced (cathode), so E°cell = 0.80 V – (-0.44 V) = 1.24 V. The potential is not multiplied by the coefficient 2.
Q58A current of 2.00 A is passed through a CuSO4 solution for 1930 s, depositing copper at the cathode by Cu^2+ + 2 e^- → Cu. What mass of Cu is deposited? (Faraday constant = 96,500 C/mol e^-; molar mass of Cu = 63.55 g/mol)
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Correct: (B)
Charge = 2.00 × 1930 = 3860 C, which is 3860/96,500 = 0.0400 mol e^-. This deposits 0.0200 mol Cu, or 0.0200 × 63.55 = 1.27 g.
Q59Which process results in an increase in the entropy of the system?
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Correct: (D)
Sublimation converts an ordered solid into a gas with far more accessible microstates, so ΔS is positive. Freezing, condensation, and compression all decrease entropy.
Q60At 298 K, an equilibrium constant of K = 1.0 × 10^6 is measured for a reaction. What is ΔG° for the reaction? (R = 8.314 J/mol·K)
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Correct: (A)
ΔG° = -RT ln K = -(8.314)(298) ln(1.0 × 10^6) = -34,200 J/mol = -34 kJ/mol.
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