ACS General Chemistry Practice Test 7
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 elements has the largest atomic radius?
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Correct: (A)
Atomic radius decreases across a period from left to right as effective nuclear charge increases, so silicon, the leftmost element, is the largest.
Q2Which of the following elements has the lowest first ionization energy?
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Correct: (C)
Ionization energy is lowest for alkali metals, and sodium holds its valence electron most loosely among these choices.
Q3What is the ground-state electron configuration of the Fe2+ ion?
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Correct: (A)
Transition metal cations lose their 4s electrons before 3d electrons, so Fe ([Ar] 4s2 3d6) loses both 4s electrons to give [Ar] 3d6.
Q4Which of the following ions is NOT isoelectronic with argon?
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Correct: (D)
K+, Ca2+, and Cl− each have 18 electrons like argon, while Mg2+ has only 10 electrons.
Q5Which of the following ions has the greatest number of unpaired electrons?
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Correct: (D)
Fe3+ is a d5 ion with 5 unpaired electrons, more than Cr2+ (d4, 4 unpaired), Ni2+ (d8, 2 unpaired), or Zn2+ (d10, 0 unpaired).
Q6Which of the following elements has the largest (most exothermic) electron affinity?
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Correct: (A)
Although electron affinity generally increases up a group, chlorine's is larger in magnitude than fluorine's because fluorine's small size causes strong electron-electron repulsion.
🔬 Chemical Bonding & Molecular Geometry
Q7What is the molecular geometry of the sulfite ion, SO3 2−?
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Correct: (C)
Sulfur has three bonding pairs and one lone pair, giving an AX3E arrangement with trigonal pyramidal geometry.
Q8Which of the following molecules is nonpolar?
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Correct: (B)
CO2 is linear, so its two equal and opposite bond dipoles cancel, while the other three have bent or pyramidal geometries with net dipoles.
Q9What is the bond order of the O2+ ion?
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Correct: (B)
O2+ has one fewer antibonding electron than O2, so its bond order is (10 − 5)/2 = 2.5.
Q10What is the hybridization of the central atom in SF4?
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Correct: (D)
Sulfur has four bonding pairs and one lone pair, requiring five electron domains and sp3d hybridization.
Q11Which of the following bonds has the shortest bond length?
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Correct: (B)
Bond length decreases as bond order increases, so the triple bond is the shortest of these carbon-carbon bonds.
Q12How many sigma (σ) and pi (π) bonds are present in one molecule of ethyne, C2H2?
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Correct: (A)
The C≡C triple bond contributes 1 σ and 2 π bonds, and each C−H single bond contributes 1 σ bond, for a total of 3 σ and 2 π.
Q13Which of the following compounds has the greatest ionic character?
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Correct: (D)
Ionic character increases with electronegativity difference, which is largest for CaO (3.44 − 1.00 = 2.44) among these choices.
🧪 Stoichiometry & Aqueous Reactions
Q14How many grams of CO2 are produced by the complete combustion of 8.00 g of methane, CH4? (Molar masses: CH4 = 16.0 g/mol, CO2 = 44.0 g/mol)
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Correct: (A)
8.00 g CH4 = 0.500 mol, and each mole of CH4 produces one mole of CO2, so 0.500 mol × 44.0 g/mol = 22.0 g.
Q15For the reaction 2 H2(g) + O2(g) → 2 H2O(l), if 5.00 mol of H2 is mixed with 2.00 mol of O2, how many moles of H2 remain unreacted?
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Correct: (D)
O2 is the limiting reactant; 2.00 mol O2 consumes 4.00 mol H2, leaving 5.00 − 4.00 = 1.00 mol H2 unreacted.
Q16What is the molarity of a solution prepared by dissolving 14.6 g of NaCl (molar mass 58.5 g/mol) in enough water to make 500. mL of solution?
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Correct: (D)
Moles NaCl = 14.6 / 58.5 = 0.250 mol, and molarity = 0.250 mol / 0.500 L = 0.500 M.
Q17In a titration, 25.0 mL of 0.100 M HCl is exactly neutralized by 20.0 mL of NaOH solution. What is the molarity of the NaOH solution?
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Correct: (B)
Moles HCl = 0.0250 L × 0.100 M = 0.00250 mol = moles NaOH, so M = 0.00250 mol / 0.0200 L = 0.125 M.
Q18What is the net ionic equation for the reaction of aqueous AgNO3 with aqueous NaCl?
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Correct: (B)
AgCl is insoluble, so Ag+ and Cl− combine to form the solid precipitate while Na+ and NO3− remain spectator ions.
Q19A reaction has a theoretical yield of 25.0 g of product. If 20.0 g is actually obtained, what is the percent yield?
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Correct: (A)
Percent yield = (20.0 g / 25.0 g) × 100% = 80.0%.
Q20What is the oxidation number of chromium in K2Cr2O7?
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Correct: (B)
With K at +1 and O at −2, solving 2(+1) + 2x + 7(−2) = 0 gives x = +6.
🌀 Gases & Intermolecular Forces
Q21A 2.00 mol sample of an ideal gas at 300. K exerts a pressure of 1.50 atm. What is its volume? (R = 0.08206 L·atm/mol·K)
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Correct: (D)
V = nRT/P = (2.00)(0.08206)(300.)/1.50 = 32.8 L.
Q22At the same temperature and pressure, hydrogen gas effuses through a small opening how many times faster than oxygen gas?
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Correct: (C)
By Graham's law, rate(H2)/rate(O2) = √(32.0/2.02) = √16 = 4.
Q23A gas mixture has a total pressure of 760. torr. If the partial pressures of O2 and N2 are 160. torr and 590. torr respectively, what is the partial pressure of Ar in the mixture?
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Correct: (C)
By Dalton's law, P(Ar) = 760. − 160. − 590. = 10. torr.
Q24Which of the following substances has the highest boiling point?
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Correct: (B)
All except CH4 can hydrogen bond, and water's extensive hydrogen-bonding network gives it the highest boiling point of the group.
Q25Between which pair of molecules can hydrogen bonding occur?
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Correct: (D)
Both NH3 and HF have hydrogen bonded directly to N or F, allowing hydrogen bonding between them; the other pairs lack H bonded to N, O, or F.
🔥 Thermochemistry
Q26The combustion of propane is exothermic. Which statement is true for this reaction?
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Correct: (A)
Exothermic reactions release heat to the surroundings, so the enthalpy change is negative.
Q27Given: C(s) + O2(g) → CO2(g), ΔH = −394 kJ; H2(g) + ½O2(g) → H2O(l), ΔH = −286 kJ; CH4(g) + 2O2(g) → CO2(g) + 2H2O(l), ΔH = −890 kJ. What is the standard enthalpy of formation of CH4(g)?
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Correct: (A)
By Hess's law, −890 = (−394 + 2(−286)) − ΔHf(CH4), so ΔHf(CH4) = −966 + 890 = −76 kJ/mol.
Q28A 50.0 g sample of a substance absorbs 2.09 kJ of heat and its temperature rises by 10.0 °C. What is its specific heat capacity?
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Correct: (C)
c = q/(m·ΔT) = 2090 J / (50.0 g × 10.0 °C) = 4.18 J/g·°C.
Q29Which of the following has a standard enthalpy of formation (ΔHf°) equal to zero?
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Correct: (A)
The standard enthalpy of formation of any element in its standard reference state, such as O2(g), is defined as zero.
Q30Using the bond energies H−H = 436 kJ/mol, Cl−Cl = 243 kJ/mol, and H−Cl = 431 kJ/mol, estimate ΔH for H2(g) + Cl2(g) → 2 HCl(g).
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Correct: (C)
ΔH ≈ (436 + 243) − 2(431) = 679 − 862 = −183 kJ, since bond breaking is endothermic and bond forming is exothermic.
Q31Given the standard enthalpies of combustion below, calculate ΔH° for the reaction: 2 CH4(g) + 3 O2(g) → 2 CO(g) + 4 H2O(l).
CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(l) ΔH° = −890 kJ
CO(g) + ½ O2(g) → CO2(g) ΔH° = −283 kJ
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Correct: (A)
2(−890) − 2(−283) = −1780 + 566 = −1214 kJ by Hess's law.
⚡ Quantum Theory & Electronic Structure
Q32Which of the following sets of quantum numbers (n, l, ml, ms) is allowed for an electron in an atom?
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Correct: (C)
l must be less than n, |ml| ≤ l, and ms = ±½; only set C satisfies all rules.
Q33What is the ground-state electron configuration of chromium (Z = 24)?
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Correct: (B)
Cr is an exception with a half-filled 4s and half-filled 3d subshell, [Ar]4s^1 3d^5.
Q34The threshold frequency for electron ejection from a certain metal is 5.5×10^14 Hz. Light of wavelength 400 nm strikes the metal surface. What is the maximum kinetic energy of the ejected electrons? (h = 6.626×10^−34 J·s)
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Correct: (D)
Photon energy hν = 4.97×10^−19 J exceeds the work function hν0 = 3.64×10^−19 J; KE = (4.97 − 3.64)×10^−19 J ≈ 1.3×10^−19 J.
Q35What is the de Broglie wavelength of an electron traveling at 2.0×10^6 m/s? (me = 9.11×10^−31 kg, h = 6.626×10^−34 J·s)
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Correct: (B)
λ = h/mv = 6.626×10^−34 / (9.11×10^−31 × 2.0×10^6) = 3.64×10^−10 m = 364 pm.
⏱ Chemical Kinetics
Q36For the reaction 2 NO(g) + O2(g) → 2 NO2(g), the following initial-rate data were collected:
Exp 1: [NO] = 0.010 M, [O2] = 0.010 M, rate = 2.0×10^−2 M/s
Exp 2: [NO] = 0.020 M, [O2] = 0.010 M, rate = 8.0×10^−2 M/s
Exp 3: [NO] = 0.010 M, [O2] = 0.030 M, rate = 6.0×10^−2 M/s
What is the rate law?
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Correct: (A)
Doubling [NO] quadruples the rate (second order in NO); tripling [O2] triples the rate (first order in O2).
Q37A first-order decomposition has a half-life of 120 s. If the initial concentration is 0.800 M, what is the concentration after 360 s?
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Correct: (D)
360 s is three half-lives, so (1/2)^3 × 0.800 M = 0.100 M remains.
Q38A first-order reaction has k = 4.2×10^−3 s^−1 at 298 K and an activation energy of 85.0 kJ/mol. What is the rate constant at 318 K? (R = 8.314 J/mol·K)
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Correct: (B)
ln(k2/k1) = (Ea/R)(1/T1 − 1/T2) = 2.16, so k2 = 4.2×10^−3 × e^2.16 ≈ 3.6×10^−2 s^−1.
Q39A proposed mechanism for 2 NO(g) + 2 H2(g) → N2(g) + 2 H2O(g) is:
Step 1 (slow): 2 NO(g) + H2(g) → N2O(g) + H2O(g)
Step 2 (fast): N2O(g) + H2(g) → N2(g) + H2O(g)
What is the rate law consistent with this mechanism?
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Correct: (C)
The rate law is determined by the slow (rate-determining) step: Rate = k[NO]^2[H2].
Q40A catalyst increases the rate constant of a reaction by a factor of 3 at 25 °C without changing the mechanism. By approximately how much does the catalyst lower the activation energy? (R = 8.314 J/mol·K)
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Correct: (A)
ΔEa = RT ln(kcat/kuncat) = (8.314)(298)ln 3 = 2.72×10^3 J/mol ≈ 2.7 kJ/mol.
Q41The rate constant of a reaction has units of s^−1. What is the overall order of the reaction?
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Correct: (B)
Units of s^−1 correspond to a first-order rate constant (rate = k[A]).
⇆ Chemical Equilibrium
Q42For H2(g) + I2(g) ⇆ 2 HI(g), Kc = 64 at 445 °C. A flask initially contains 0.10 M H2 and 0.10 M I2 with no HI. What is the equilibrium concentration of HI?
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Correct: (D)
Let x = amount reacted: 2x/(0.10 − x) = √64 = 8, giving x = 0.080 M, so [HI] = 2x = 0.16 M.
Q43For the reaction 2 SO2(g) + O2(g) ⇆ 2 SO3(g), what is the relationship between Kp and Kc?
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Correct: (C)
Δn = 2 − 3 = −1, so Kp = Kc(RT)^Δn = Kc/(RT).
Q44Consider N2O4(g) ⇆ 2 NO2(g), ΔH° = +57 kJ/mol. NO2 is a brown gas; N2O4 is colorless. A piston compresses the equilibrium mixture to half its volume at constant temperature. What happens?
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Correct: (D)
Decreasing volume favors fewer moles of gas (N2O4), reducing brown NO2, so the color fades.
Q45The Ksp of PbI2 is 9.8×10^−9 at 25 °C. What is the molar solubility of PbI2 in pure water?
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Correct: (A)
Ksp = 4s^3, so s = (9.8×10^−9/4)^1/3 = 1.3×10^−3 M.
Q46For N2(g) + 3 H2(g) ⇆ 2 NH3(g), Kc = 4.0×10^−2 at a certain temperature. A mixture contains [N2] = 0.20 M, [H2] = 0.50 M, and [NH3] = 0.050 M. In which direction will the reaction proceed?
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Correct: (B)
Q = (0.050)^2/[(0.20)(0.50)^3] = 0.10 > Kc, so the reaction shifts toward reactants.
Q47Which of the following, when added to a saturated solution of AgCl, will increase the molar solubility of AgCl?
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Correct: (D)
NH3 forms the complex ion [Ag(NH3)2]^+, removing Ag^+ and shifting dissolution forward; the others add a common ion or are inert.
🧫 Acids, Bases & Buffers
Q48A 0.10 M solution of a weak monoprotic acid HA has a pH of 3.46. What is the Ka of HA?
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Correct: (B)
[H^+] = 10^−3.46 = 3.47×10^−4 M; Ka = (3.47×10^−4)^2/0.10 ≈ 1.2×10^−6.
Q49Which of the following mixtures forms an effective buffer with pH near 3.1? (Ka of HF = 6.8×10^−4)
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Correct: (A)
A weak acid plus its conjugate base in comparable amounts buffers near its pKa (3.17); the others contain a strong acid/base or neutralize all of the weak acid.
Q5025.0 mL of 0.10 M NH3 (Kb = 1.8×10^−5) is titrated with 0.10 M HCl. What is the pH at the equivalence point?
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Correct: (D)
At equivalence [NH4^+] = 0.050 M; Ka(NH4^+) = Kw/Kb = 5.6×10^−10; [H^+] = √(Ka·C) = 5.3×10^−6 M, pH = 5.28.
Q51What is the pH of a buffer containing 0.30 M CH3COOH and 0.20 M CH3COONa? (Ka = 1.8×10^−5)
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Correct: (B)
pH = pKa + log([base]/[acid]) = 4.74 + log(0.20/0.30) = 4.74 − 0.18 = 4.57.
Q52Which 0.10 M salt solution has the highest pH?
Ka values: HF = 7.2×10^−4, HNO2 = 7.1×10^−4, HClO2 = 1.1×10^−2, HCN = 6.2×10^−10
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Correct: (D)
The anion of the weakest acid (HCN) hydrolyzes most, giving the most basic solution.
Q53For phosphoric acid, pKa1 = 2.15, pKa2 = 7.21, pKa3 = 12.37. Which species predominates in aqueous solution at pH 10.0?
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Correct: (C)
At pH 10.0, between pKa2 and pKa3, the dominant species is HPO4^2−.
🔋 Thermodynamics & Electrochemistry
Q54For which reaction is ΔS° expected to be positive?
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Correct: (A)
A gas is produced from liquids, increasing molecular disorder; the others decrease moles of gas or increase order.
Q55For a reaction, ΔH° = −92 kJ/mol and ΔS° = −199 J/mol·K. What is ΔG° at 298 K, and is the reaction spontaneous under standard conditions?
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Correct: (A)
ΔG° = ΔH° − TΔS° = −92,000 − 298(−199) = −32,700 J/mol ≈ −33 kJ/mol < 0, so spontaneous.
Q56For a reaction with K = 1.2×10^5 at 298 K, what is ΔG°? (R = 8.314 J/mol·K)
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Correct: (B)
ΔG° = −RT ln K = −(8.314)(298)ln(1.2×10^5) = −2.90×10^4 J/mol ≈ −29.0 kJ/mol.
Q57A galvanic cell is constructed from Zn(s)|Zn^2+(1.0 M) and Cu^2+(1.0 M)|Cu(s) half-cells. Given E°(Cu^2+/Cu) = +0.34 V and E°(Zn^2+/Zn) = −0.76 V, what is E°cell?
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Correct: (C)
E°cell = E°cathode − E°anode = 0.34 − (−0.76) = 1.10 V, with Zn oxidized.
Q58For the cell Cu(s)|Cu^2+(0.010 M)||Ag^+(1.0 M)|Ag(s) at 25 °C, E°cell = 0.46 V. What is the cell potential E? (2 Ag^+ + Cu → 2 Ag + Cu^2+)
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Correct: (C)
E = E° − (0.0592/2)log([Cu^2+]/[Ag^+]^2) = 0.46 − 0.0296(−2) = 0.52 V.
☢ Nuclear & Descriptive Chemistry
Q59Plutonium-239 undergoes alpha decay. What is the balanced nuclear equation?
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Correct: (D)
Alpha emission reduces the mass number by 4 and the atomic number by 2: 239 − 4 = 235, 94 − 2 = 92 (U).
Q60An unknown substance is a colorless gas with a pungent odor that turns moist red litmus paper blue. What is the gas?
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Correct: (A)
Ammonia is a basic gas (turns red litmus blue); the others are acidic gases.
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