ACS General Chemistry Practice Test 17
60 original exam-style multiple-choice questions with answers & explanations — covering every major topic tested on the ACS General Chemistry exam.
Note: These are original practice questions written in the ACS exam style — not reproduced exam questions. Use them to test your readiness for the real ACS General Chemistry exam.
📱 How to use: Try each question first, then click “Show Answer” to check. Covers: atomic structure, bonding, stoichiometry, gases, thermochemistry, kinetics, equilibrium, acids & bases, electrochemistry and more.
⚛ Atomic Structure & Periodic Trends
Q1Which of the following is the ground-state electron configuration of a neutral chromium atom?
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Correct: (B)
A half-filled 3d subshell plus a half-filled 4s subshell is more stable than [Ar]4s2 3d4, so one 4s electron is promoted to 3d.
Q2Which element has the largest first ionization energy?
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Correct: (D)
Ionization energy generally increases across a period and decreases down a group; neon, a Period 2 noble gas, has the highest first ionization energy of these.
Q3Which of the following lists the atoms in order of decreasing atomic radius?
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Correct: (C)
Atomic radius increases down a group because additional electron shells are added, so iodine is the largest and fluorine the smallest.
Q4Which ion is NOT isoelectronic with a neon atom?
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Correct: (D)
F−, Na+, and Mg2+ each have 10 electrons like neon, but Cl− has 18 electrons.
Q5A photon with a wavelength of 500. nm strikes a metal surface whose work function is 3.30 × 10−19 J. What is the kinetic energy of the ejected electron? (h = 6.626 × 10−34 J·s, c = 3.00 × 108 m/s)
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Correct: (A)
The photon energy is hc/λ = 3.98 × 10−19 J, which exceeds the work function, so KE = 3.98 × 10−19 − 3.30 × 10−19 = 6.8 × 10−20 J.
Q6Which set of quantum numbers (n, l, ml) is NOT possible for an electron in an atom?
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Correct: (B)
The magnetic quantum number ml must satisfy |ml| ≤ l, so ml = −3 is impossible when l = 2.
🔬 Chemical Bonding & Molecular Geometry
Q7What is the molecular geometry of XeF4?
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Correct: (A)
Xenon has 6 electron domains (4 bonding pairs + 2 lone pairs); the two lone pairs occupy axial positions of the octahedral arrangement, leaving a square planar shape.
Q8What is the hybridization of the sulfur atom in SF4?
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Correct: (D)
Sulfur has 5 electron domains (4 bonding pairs + 1 lone pair), which requires sp3d hybridization.
Q9Which molecule has a nonzero net dipole moment?
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Correct: (C)
H2O is bent, so its bond dipoles do not cancel; the other three are symmetric and nonpolar.
Q10Which species has the shortest carbon–oxygen bond?
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Correct: (B)
Carbon monoxide has a C≡O triple bond (bond order 3), and bond length decreases as bond order increases.
Q11How many lone pairs are on the central xenon atom in XeF2?
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Correct: (A)
Xenon contributes 8 valence electrons and each F contributes 1, giving 5 electron domains (2 bonding + 3 lone pairs) in a linear arrangement.
Q12In the best Lewis structure of the nitrate ion, NO3−, what is the formal charge on the nitrogen atom?
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Correct: (C)
Formal charge = 5 − (0 + 8/2) = +1; the negative charge of the ion is distributed over the oxygen atoms.
Q13Which bond is the most polar?
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Correct: (A)
The C–F bond has the largest electronegativity difference (4.0 − 2.5 = 1.5), giving it the greatest bond polarity.
🧪 Stoichiometry & Aqueous Reactions
Q14What mass of CO2 is produced when 25.0 g of CaCO3 decomposes completely according to CaCO3 → CaO + CO2?
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Correct: (C)
25.0 g CaCO3 ÷ 100.09 g/mol = 0.2498 mol, producing 0.2498 mol × 44.01 g/mol = 11.0 g of CO2.
Q15How many moles of H2O can be formed from 4.0 mol of H2 and 1.5 mol of O2 in the reaction 2H2 + O2 → 2H2O?
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Correct: (B)
O2 is limiting (1.5 mol O2 requires only 3.0 mol H2), so 2 × 1.5 = 3.0 mol of H2O forms.
Q16What is the molarity of the solution when 50.0 mL of 3.00 M NaOH is diluted with water to a final volume of 250. mL?
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Correct: (A)
M2 = M1V1/V2 = (3.00 M)(50.0 mL)/(250. mL) = 0.600 M.
Q17What is the net ionic equation for the reaction of aqueous silver nitrate with aqueous sodium chloride?
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Correct: (C)
AgCl precipitates; Na+ and NO3− are spectator ions and cancel from the net ionic equation.
Q18What is the oxidation number of chromium in K2Cr2O7?
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Correct: (D)
With K at +1 and O at −2: 2(+1) + 2x + 7(−2) = 0 gives x = +6.
Q19A compound contains 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. What is its empirical formula?
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Correct: (C)
The mole ratio is 3.33 mol C : 6.7 mol H : 3.33 mol O, which simplifies to 1:2:1, giving CH2O.
Q20How many milliliters of 0.200 M H2SO4 are required to neutralize 30.0 mL of 0.100 M NaOH? (H2SO4 + 2NaOH → Na2SO4 + 2H2O)
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Correct: (D)
3.00 mmol NaOH requires 1.50 mmol H2SO4 (2:1 ratio), and 1.50 mmol ÷ 0.200 M = 7.50 mL.
🌀 Gases & Intermolecular Forces
Q21What is the volume occupied by 0.500 mol of an ideal gas at 2.00 atm and 300. K? (R = 0.08206 L·atm/mol·K)
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Correct: (C)
V = nRT/P = (0.500)(0.08206)(300.)/(2.00) = 6.15 L.
Q22Which gas effuses the fastest at the same temperature?
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Correct: (D)
By Graham's law, effusion rate is inversely proportional to the square root of molar mass, so helium (4.00 g/mol) is fastest.
Q23Which gas would show the greatest deviation from ideal behavior at high pressure and low temperature?
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Correct: (B)
Xenon has the largest, most polarizable electron cloud, so its intermolecular attractions cause the largest deviation from ideality.
Q24Which liquid has the highest boiling point?
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Correct: (D)
Ethanol can hydrogen bond, the strongest intermolecular force among these choices, giving it the highest boiling point.
Q25A gas mixture contains 2.0 mol N2 and 3.0 mol O2 at a total pressure of 750 torr. What is the partial pressure of O2?
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Correct: (B)
By Dalton's law, PO2 = (3.0/5.0) × 750 torr = 450 torr.
🔥 Thermochemistry
Q26How much heat is absorbed when 100.0 g of water is heated from 25.0°C to 35.0°C? (specific heat of water = 4.184 J/g·°C)
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Correct: (D)
q = mcΔT = (100.0 g)(4.184 J/g·°C)(10.0°C) = 4184 J = 4.18 kJ.
Q27For which process is ΔH negative?
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Correct: (A)
Combustion releases heat to the surroundings, so it is exothermic and ΔH < 0; the others absorb heat.
Q28Given (1) C(s) + O2(g) → CO2(g), ΔH = −393.5 kJ and (2) CO(g) + ½O2(g) → CO2(g), ΔH = −283.0 kJ, what is ΔH for C(s) + ½O2(g) → CO(g)?
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Correct: (C)
By Hess's law, subtract reaction (2) from reaction (1): −393.5 − (−283.0) = −110.5 kJ.
Q29Using ΔHf° values, what is ΔH°rxn for 2H2(g) + O2(g) → 2H2O(l)? (ΔHf°[H2O(l)] = −285.8 kJ/mol)
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Correct: (A)
ΔH°rxn = 2(−285.8) − 0 = −571.6 kJ, since elements in standard states have ΔHf° = 0.
Q30The same quantity of heat is added to each of the following samples. Which undergoes the smallest temperature increase?
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Correct: (D)
Temperature change is q/(mc); 50.0 g Al has the largest heat capacity (44.9 J/°C), so it warms the least.
Q31Use the average bond enthalpies below to estimate ΔH° for the gas-phase reaction H2(g) + Br2(g) → 2HBr(g). Bond enthalpies (kJ/mol): H−H = 436, Br−Br = 193, H−Br = 366.
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Correct: (B)
ΔH = (bonds broken) − (bonds formed) = (436 + 193) − 2(366) = −103 kJ; the reaction is exothermic because two strong H−Br bonds form.
⚡ Quantum Theory & Electronic Structure
Q32The work function of a certain metal is 3.20 eV. Light of wavelength 300 nm strikes the metal surface. What is the maximum kinetic energy of an ejected electron? (hc = 1240 eV·nm)
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Correct: (C)
Photon energy = 1240/300 = 4.13 eV; KE = hν − work function = 4.13 − 3.20 = 0.93 eV (photoelectric effect).
Q33Which set of quantum numbers (n, l, ml, ms) is allowed for an electron in an atom?
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Correct: (D)
Valid sets require l < n, |ml| ≤ l; only (D) satisfies all quantum number rules.
Q34The Fe3+ ion has five unpaired electrons. Which of the following species has the same number of unpaired electrons?
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Correct: (A)
Mn2+ is [Ar]3d5 with five unpaired electrons, matching the d5 configuration of Fe3+ (Hund's rule maximizes unpaired electrons in degenerate orbitals).
Q35What is the de Broglie wavelength of an electron traveling at 2.00×10^6 m/s? (h = 6.626×10^−34 J·s; me = 9.109×10^−31 kg)
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Correct: (B)
λ = h/mv = 6.626×10^−34 / (9.109×10^−31 × 2.00×10^6) = 3.64×10^−10 m.
⏱ Chemical Kinetics
Q36A reaction proceeds by the mechanism: Step 1: A + B ⇌ C (fast equilibrium); Step 2: C → D (slow). What is the rate law for the overall reaction?
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Correct: (C)
The slow step gives rate = k2[C], and the fast pre-equilibrium gives [C] proportional to [A][B], so the overall rate law is first order in each reactant.
Q37For a first-order decomposition, the concentration of reactant falls from 0.80 M to 0.20 M in 240 s. What is the half-life of the reaction?
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Correct: (D)
Falling from 0.80 to 0.20 M is two half-lives (0.80 → 0.40 → 0.20), so t1/2 = 240/2 = 120 s.
Q38The rate constant for a reaction is 2.0×10^−3 s^−1 at 300 K and 4.0×10^−3 s^−1 at 310 K. What is the activation energy? (R = 8.314 J/mol·K)
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Correct: (A)
From the two-point Arrhenius equation, Ea = R·ln(k2/k1)/(1/T1 − 1/T2) = 8.314·ln2/(1/300 − 1/310) = 5.4×10^4 J/mol.
Q39For a reaction that is second order in a single reactant A, which plot gives a straight line?
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Correct: (B)
The integrated second-order rate law is 1/[A]t = kt + 1/[A]0, so 1/[A] vs. t is linear with slope k.
Q40For the reaction 2NO(g) + O2(g) → 2NO2(g), the following initial-rate data were obtained: Exp 1: [NO] = 0.10 M, [O2] = 0.10 M, rate = 0.020 M/s; Exp 2: [NO] = 0.20 M, [O2] = 0.10 M, rate = 0.080 M/s; Exp 3: [NO] = 0.10 M, [O2] = 0.20 M, rate = 0.040 M/s. What is the rate law?
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Correct: (D)
Doubling [NO] quadruples the rate (second order in NO); doubling [O2] doubles the rate (first order in O2).
Q41Which statement about a catalyst is correct?
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Correct: (A)
A catalyst lowers Ea by offering a different mechanism but does not change ΔH, K, or appear in the net equation.
⇆ Chemical Equilibrium
Q42For N2(g) + 3H2(g) ⇌ 2NH3(g) at equilibrium, [N2] = 0.10 M, [H2] = 0.20 M, and [NH3] = 0.40 M. What is Kc?
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Correct: (B)
Kc = [NH3]^2/([N2][H2]^3) = (0.40)^2/(0.10 × 0.20^3) = 0.16/8.0×10^−4 = 200.
Q43Consider 2SO2(g) + O2(g) ⇌ 2SO3(g), ΔH° < 0. Which change will increase the equilibrium yield of SO3?
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Correct: (C)
The reaction is exothermic, so lowering the temperature shifts equilibrium toward products (Le Châtelier's principle); catalysts and inert gas at constant V do not shift K.
Q44The Ksp of the sparingly soluble salt AB3 (which dissociates as AB3(s) ⇌ A3+ + 3B−) is 2.7×10^−9. What is its molar solubility?
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Correct: (A)
Ksp = (s)(3s)^3 = 27s^4, so s = (2.7×10^−9/27)^1/4 = (1.0×10^−10)^1/4 = 3.2×10^−3 M.
Q45For the reaction PCl5(g) ⇌ PCl3(g) + Cl2(g), what is the relationship between Kp and Kc?
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Correct: (D)
Kp = Kc(RT)^Δn with Δn = (1 + 1) − 1 = +1, so Kp = Kc(RT).
Q46For 2A(g) + B(g) ⇌ 3C(g), Kc = 4.0×10^3. At a certain moment, [A] = 0.50 M, [B] = 0.20 M, and [C] = 2.0 M. In which direction will the reaction proceed?
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Correct: (B)
Q = [C]^3/([A]^2[B]) = 8.0/(0.25 × 0.20) = 160 < Kc, so the system shifts right to reach equilibrium.
Q47What is the equilibrium constant expression for CaCO3(s) ⇌ CaO(s) + CO2(g)?
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Correct: (C)
Pure solids are omitted from equilibrium expressions, leaving Kc = [CO2] (heterogeneous equilibrium).
🧫 Acids, Bases & Buffers
Q48What is the pH of a 0.10 M solution of a weak acid HA with Ka = 1.8×10^−5?
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Correct: (D)
[H+] ≈ √(Ka·C) = √(1.8×10^−6) = 1.34×10^−3 M, so pH = 2.87.
Q49The Ka of the ammonium ion (NH4+) is 5.6×10^−10. What is the Kb of ammonia (NH3)?
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Correct: (A)
For a conjugate pair, Ka·Kb = Kw, so Kb = 1.0×10^−14/5.6×10^−10 = 1.8×10^−5.
Q50Which of the following mixtures constitutes a buffer solution?
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Correct: (C)
A buffer requires a weak acid and its conjugate base (or weak base and conjugate acid); only (C) contains such a pair.
Q51In the titration of a weak acid with a strong base, the pH at the equivalence point is
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Correct: (B)
At the equivalence point only the conjugate base remains, and its hydrolysis produces OH−, making the solution basic.
Q52What is the pH of a buffer containing 0.20 M CH3COOH and 0.10 M CH3COONa? (Ka = 1.8×10^−5)
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Correct: (D)
By the Henderson–Hasselbalch equation, pH = pKa + log([base]/[acid]) = 4.74 + log(0.10/0.20) = 4.44.
Q53A 0.50 M solution of HF is 4.0% ionized. What is the Ka of HF?
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Correct: (A)
[H+] = 0.50 × 0.040 = 0.020 M; Ka = (0.020)^2/(0.50 − 0.020) = 8.3×10^−4.
🔋 Thermodynamics & Electrochemistry
Q54What is the sign of ΔS° for the reaction 2H2O2(l) → 2H2O(l) + O2(g)?
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Correct: (C)
A gas is produced from liquids only, increasing the number of microstates, so entropy increases.
Q55A reaction has ΔH° = +91 kJ/mol and ΔS° = +190 J/mol·K. Above what temperature does the reaction become spontaneous?
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Correct: (B)
Spontaneity requires ΔG = ΔH − TΔS < 0; with both terms positive this occurs when T > ΔH/ΔS = 91000/190 ≈ 480 K.
Q56Given Zn2+ + 2e− → Zn, E° = −0.76 V and Cu2+ + 2e− → Cu, E° = +0.34 V, what is E°cell for the spontaneous Zn–Cu galvanic cell?
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Correct: (D)
E°cell = E°cathode − E°anode = (+0.34) − (−0.76) = +1.10 V (Cu2+ is reduced, Zn is oxidized).
Q57For the Zn–Cu galvanic cell (E°cell = 1.10 V) at 25°C with [Zn2+] = 1.0 M and [Cu2+] = 0.010 M, what is the cell potential?
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Correct: (A)
By the Nernst equation, E = E° − (0.0592/2)log([Zn2+]/[Cu2+]) = 1.10 − 0.0296·log(100) = 1.04 V.
Q58A current of 0.500 A is passed through molten CuSO4 for 30.0 minutes. What mass of copper metal is deposited at the cathode? (Cu = 63.55 g/mol)
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Correct: (C)
Charge = 0.500 × 1800 = 900 C = 9.33×10^−3 mol e−; Cu2+ requires 2 e−, giving 4.66×10^−3 mol Cu = 0.296 g (Faraday's law).
☢ Nuclear & Descriptive Chemistry
Q59Plutonium-239 undergoes alpha decay. Which equation correctly represents this nuclear reaction?
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Correct: (D)
Alpha emission reduces the mass number by 4 and the atomic number by 2: ^239(94)Pu → ^235(92)U + ^4(2)He.
Q60Which oxide dissolves in both aqueous sodium hydroxide and aqueous hydrochloric acid?
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Correct: (B)
Al2O3 is amphoteric, reacting with both strong acids and strong bases; CO2 and SO2 are acidic oxides, MgO is basic.
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