ACS General Chemistry Practice Test 8
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
Q1The ground-state electron configuration of the Fe2+ ion is
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Correct: (C)
When a transition metal forms a cation, the 4s electrons are removed before the 3d electrons, giving [Ar] 3d6.
Q2Which of the following elements has the greatest first ionization energy?
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Correct: (D)
First ionization energy generally increases across a period because effective nuclear charge increases; Si has the largest effective nuclear charge of the four.
Q3Arrange the following atoms in order of decreasing atomic radius.
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Correct: (B)
Atomic radius decreases from left to right across a period, so K > Ca > Ga > As.
Q4Which of the following isoelectronic species has the largest ionic radius?
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Correct: (A)
All four species have 10 electrons; the one with the fewest protons (O2−, Z = 8) exerts the weakest pull on the electron cloud and is largest.
Q5Which set of quantum numbers (n, l, ml, ms) is NOT allowed for an electron in an atom?
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Correct: (B)
For n = 2, the allowed values of l are 0 and 1 only; l = 2 is not permitted.
Q6How many unpaired electrons are present in a ground-state atom of manganese (Z = 25)?
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Correct: (D)
The configuration is [Ar] 4s2 3d5, with each of the five d orbitals singly occupied.
🔬 Chemical Bonding & Molecular Geometry
Q7Which molecule has a tetrahedral electron-pair geometry but a trigonal pyramidal molecular geometry?
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Correct: (B)
NH3 has three bonding pairs and one lone pair on nitrogen, giving a trigonal pyramidal shape from a tetrahedral electron arrangement.
Q8What is the formal charge on the chlorine atom in the chlorate ion, ClO3−?
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Correct: (C)
FC = 7 valence e− − 2 nonbonding e− − (6 bonding e−/2) = +2.
Q9In which molecule is the bond angle closest to 180°?
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Correct: (A)
CO2 is linear with a 180° bond angle; the others are bent, pyramidal, or tetrahedral.
Q10Which molecule is nonpolar even though it contains polar bonds?
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Correct: (D)
The linear geometry of CO2 causes the two equal and opposite C=O bond dipoles to cancel.
Q11What is the hybridization of the xenon atom in XeF4?
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Correct: (A)
Xenon has six electron domains (four bonds and two lone pairs), requiring sp3d2 hybridization.
Q12Which of the following molecules has an expanded octet on its central atom?
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Correct: (B)
Sulfur in SF6 is surrounded by 12 valence electrons, which is possible for a third-period element.
Q13According to molecular orbital theory, which diatomic species has the highest bond order?
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Correct: (C)
N2 has a bond order of 3, higher than NO (2.5), O2 (2), or N2+ (2.5).
🧪 Stoichiometry & Aqueous Reactions
Q14Calcium carbonate decomposes on heating: CaCO3(s) → CaO(s) + CO2(g). What mass of CaCO3 (molar mass 100.1 g/mol) must be heated to produce 44.0 g of CO2?
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Correct: (A)
44.0 g CO2 = 1.00 mol; the 1:1 mole ratio requires 1.00 mol CaCO3, which is about 100 g.
Q15Consider the reaction N2(g) + 3H2(g) → 2NH3(g). If 4.0 mol of N2 is mixed with 9.0 mol of H2, what is the maximum number of moles of NH3 that can form?
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Correct: (B)
H2 is the limiting reactant: 9.0 mol H2 × (2 mol NH3 / 3 mol H2) = 6.0 mol NH3.
Q16What is the mass percent of oxygen in magnesium nitrate, Mg(NO3)2?
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Correct: (D)
(6 × 16.00 g/mol) / (148.3 g/mol) × 100% = 64.7%.
Q17A precipitate forms when which pair of 0.10 M aqueous solutions are mixed?
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Correct: (C)
AgCl is insoluble, so mixing AgNO3 with NaCl produces a white precipitate.
Q18What is the net ionic equation for the reaction of aqueous hydrochloric acid with aqueous sodium hydroxide?
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Correct: (A)
The spectator ions Na+ and Cl− cancel, leaving H+ + OH− → H2O.
Q19What is the oxidation number of chromium in potassium dichromate, K2Cr2O7?
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Correct: (D)
2(+1) + 2x + 7(−2) = 0 gives x = +6.
Q20What volume of 6.0 M HCl is needed to prepare 250 mL of 1.5 M HCl?
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Correct: (B)
M1V1 = M2V2 gives V1 = (1.5 × 250) / 6.0 = 62.5 mL.
🌀 Gases & Intermolecular Forces
Q21A sample of helium gas occupies 3.00 L at 1.50 atm. If the temperature is held constant and the pressure is increased to 3.00 atm, what is the new volume?
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Correct: (C)
By Boyle's law, V2 = (3.00 L × 1.50 atm) / 3.00 atm = 1.50 L.
Q22A gas sample occupies 2.50 L at 25 °C and 0.980 atm. What volume will it occupy at STP (0 °C and 1.00 atm)?
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Correct: (A)
V2 = 2.50 × (273/298) × (0.980/1.00) = 2.24 L.
Q23A 3.20 g sample of an unknown gas occupies 2.00 L at 27 °C and 1.25 atm. What is the molar mass of the gas?
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Correct: (D)
n = PV/RT = (1.25 × 2.00)/(0.08206 × 300) = 0.102 mol; M = 3.20 g / 0.102 mol = 31.5 g/mol.
Q24Which gas is expected to deviate most from ideal behavior at high pressure and moderate temperature?
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Correct: (B)
NH3 has the strongest intermolecular attractions (hydrogen bonding), causing the largest deviation from ideality.
Q25Which of the following substances has the highest boiling point?
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Correct: (C)
Methanol forms hydrogen bonds, which are stronger than the dipole-dipole and London forces in the others.
🔥 Thermochemistry
Q26How much heat is required to raise the temperature of 150 g of water from 20 °C to 60 °C? (specific heat of water = 4.184 J/g·°C)
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Correct: (D)
q = 150 × 4.184 × 40 = 2.51 × 10^4 J = 25.1 kJ.
Q27A 50.0 g piece of metal at 90.0 °C is placed in 100.0 g of water at 25.0 °C. The final equilibrium temperature is 28.3 °C. What is the approximate specific heat of the metal?
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Correct: (A)
Heat lost by metal = heat gained by water: 50.0 × c × 61.7 = 100.0 × 4.184 × 3.3, giving c = 0.45 J/g·°C.
Q28Using standard enthalpies of formation (ΔHf° in kJ/mol: CH4(g) = −74.8, CO2(g) = −393.5, H2O(l) = −285.8), calculate ΔH° for the combustion of methane: CH4(g) + 2O2(g) → CO2(g) + 2H2O(l).
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Correct: (B)
ΔH° = [−393.5 + 2(−285.8)] − (−74.8) = −890 kJ.
Q29Which statement is true for an exothermic chemical reaction?
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Correct: (C)
In an exothermic reaction the system releases heat, so the enthalpy change is negative.
Q30Given: (1) C(s) + O2(g) → CO2(g), ΔH = −393.5 kJ; (2) CO(g) + 1/2 O2(g) → CO2(g), ΔH = −283.0 kJ. Use Hess's law to find ΔH for: C(s) + 1/2 O2(g) → CO(g).
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Correct: (A)
Reversing reaction (2) and adding it to reaction (1) gives ΔH = −393.5 − (−283.0) = −110.5 kJ.
Q31A 48.2 g sample of an unknown metal at 95.3 °C is placed into 120.0 g of water at 22.1 °C in an insulated calorimeter. The final equilibrium temperature is 26.8 °C. What is the specific heat capacity of the metal? (c_water = 4.184 J/(g·°C))
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Correct: (C)
Heat lost by metal = heat gained by water; c = (120.0)(4.184)(4.7)/(48.2)(68.5) = 0.715 J/(g·°C).
⚡ Quantum Theory & Electronic Structure
Q32Which set of quantum numbers could describe an electron in an atom?
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Correct: (A)
l must be less than n and |ml| ≤ l; only (A) satisfies all rules.
Q33An electron in a hydrogen atom falls from n = 3 to n = 2. What is the wavelength of the emitted photon? (R_H = 1.097 × 10^7 m^−1)
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Correct: (D)
1/λ = R_H(1/2^2 − 1/3^2) = R_H(5/36), giving λ = 6.56 × 10^−7 m = 656 nm.
Q34What is the ground-state electron configuration of a copper atom (Z = 29)?
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Correct: (B)
Copper adopts [Ar] 4s^1 3d^10 because a completely filled 3d subshell is especially stable.
Q35Which of the following ions is diamagnetic?
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Correct: (D)
Zn^2+ is [Ar] 3d^10 with all electrons paired; the others have unpaired 3d electrons.
⏱ Chemical Kinetics
Q36For the reaction X + Y → Z, the following initial-rate data were collected:
Exp 1: [X] = 0.10 M, [Y] = 0.10 M, rate = 2.5 × 10^−4 M/s
Exp 2: [X] = 0.20 M, [Y] = 0.10 M, rate = 1.0 × 10^−3 M/s
Exp 3: [X] = 0.10 M, [Y] = 0.30 M, rate = 7.5 × 10^−4 M/s
What is the rate law?
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Correct: (B)
Doubling [X] quadruples the rate (second order in X); tripling [Y] triples the rate (first order in Y).
Q37A first-order reaction has a half-life of 45.0 min. What fraction of the reactant remains after 3.00 h?
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Correct: (C)
3.00 h = 180 min = 4 half-lives, so (1/2)^4 = 1/16 remains.
Q38The activation energy of a reaction is 75.0 kJ/mol. By what factor does the rate constant increase when the temperature is raised from 300 K to 310 K?
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Correct: (D)
ln(k2/k1) = (Ea/R)(1/T1 − 1/T2) = 0.970, so k2/k1 = e^0.970 ≈ 2.6.
Q39The reaction A + 2B → C has the experimentally determined rate law rate = k[A][B]. Which mechanism is consistent with this rate law?
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Correct: (A)
The rate law is set by the slow step; only (A) has a slow step whose molecularity gives k[A][B].
Q40A first-order reaction has k = 0.025 s^−1. If [A]0 = 0.80 M, what is [A] after 60 s?
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Correct: (A)
ln[A] = ln(0.80) − (0.025)(60), so [A] = 0.80e^−1.5 = 0.18 M.
Q41A catalyst lowers the activation energy of a reaction from 120 kJ/mol to 85 kJ/mol at 298 K. By approximately what factor does the rate constant increase?
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Correct: (D)
k_cat/k_uncat = e^(ΔEa/RT) = e^(35000/(8.314·298)) ≈ 1.4 × 10^6.
⇆ Chemical Equilibrium
Q42For N2(g) + 3H2(g) ⇌ 2NH3(g), Kc = 0.060 at 400 K. What is Kp at this temperature?
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Correct: (A)
Kp = Kc(RT)^Δn with Δn = −2; Kp = 0.060/(0.08206 · 400)^2 = 5.6 × 10^−5.
Q43For N2O4(g) ⇌ 2NO2(g), Kc = 0.36 at a certain temperature. If 0.20 M N2O4 is placed in a flask and allowed to reach equilibrium, what is [NO2]?
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Correct: (C)
Using the small-x approximation: x^2/0.20 = 0.36 gives x = 0.27 M for [NO2].
Q44For 2SO2(g) + O2(g) ⇌ 2SO3(g), Kc = 280. In a mixture with [SO2] = 0.15 M, [O2] = 0.10 M, and [SO3] = 0.90 M, in which direction will the reaction proceed?
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Correct: (D)
Q = (0.90)^2/((0.15)^2(0.10)) = 360 > Kc, so the system shifts toward reactants.
Q45For the exothermic reaction N2(g) + 3H2(g) ⇌ 2NH3(g), which change increases the equilibrium yield of NH3?
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Correct: (C)
Decreasing the volume shifts equilibrium toward the side with fewer gas moles (2 vs 4), favoring NH3.
Q46For CaCO3(s) ⇌ CaO(s) + CO2(g), which expression correctly gives the equilibrium constant?
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Correct: (A)
Pure solids are omitted from the equilibrium expression, leaving K = P(CO2).
Q47The Ksp of Ag2CrO4 is 1.1 × 10^−12. What is its molar solubility in water?
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Correct: (B)
Ksp = (2s)^2(s) = 4s^3 = 1.1 × 10^−12, so s = 6.5 × 10^−5 M.
🧫 Acids, Bases & Buffers
Q48What is the pH of 0.020 M HNO3?
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Correct: (C)
HNO3 is a strong acid, so pH = −log(0.020) = 1.70.
Q49A 0.10 M solution of the weak acid HA has a pH of 3.5. What is the pKa of HA?
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Correct: (D)
Ka = [H+]^2/[HA] = (3.16 × 10^−4)^2/0.10 = 1.0 × 10^−6, so pKa = 6.0.
Q50What is the pH of a buffer containing 0.10 M HF and 0.15 M NaF? (Ka of HF = 6.8 × 10^−4)
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Correct: (C)
pH = pKa + log([base]/[acid]); pKa = −log(6.8×10^−4) = 3.17, so pH = 3.17 + log(0.15/0.10) = 3.35.
Q5125.0 mL of 0.10 M HCN (Ka = 4.9 × 10^−10) is titrated with 0.10 M NaOH. What is the pH at the equivalence point?
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Correct: (D)
At equivalence [CN−] = 0.050 M; Kb = 2.0 × 10^−5, [OH−] = √(2.0 × 10^−5 · 0.050) = 1.0 × 10^−3 M, so pH = 11.0.
Q52Which species is the conjugate base of H2PO4−?
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Correct: (B)
Removing one proton from H2PO4− gives HPO4^2−.
Q53What is the pH of 0.010 M Ba(OH)2?
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Correct: (A)
[OH−] = 0.020 M, so pOH = 1.70 and pH = 14.00 − 1.70 = 12.30.
🔋 Thermodynamics & Electrochemistry
Q54Using S° values (J/(mol·K)): H2(g) = 131, O2(g) = 205, H2O(l) = 70, what is ΔS° for 2H2(g) + O2(g) → 2H2O(l)?
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Correct: (B)
ΔS° = 2(70) − [2(131) + 205] = −327 J/(mol·K).
Q55For a reaction with ΔH° = −92 kJ/mol and ΔS° = −199 J/(mol·K), what is ΔG° at 298 K?
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Correct: (C)
ΔG° = ΔH° − TΔS° = −92 − (298)(−0.199) = −33 kJ/mol.
Q56Consider the galvanic cell Zn(s) | Zn^2+ (1.0 M) || Cu^2+ (1.0 M) | Cu(s). Given E°(Zn^2+/Zn) = −0.76 V and E°(Cu^2+/Cu) = +0.34 V, what is E°cell and which electrode is the anode?
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Correct: (B)
E°cell = 0.34 − (−0.76) = 1.10 V; zinc is oxidized, so Zn is the anode.
Q57For the cell Zn(s) | Zn^2+ (0.10 M) || Cu^2+ (1.0 M) | Cu(s) at 25 °C, what is the cell potential? (E°cell = 1.10 V)
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Correct: (C)
E = 1.10 − (0.0592/2)log(0.10/1.0) = 1.10 + 0.0296 = 1.13 V.
Q58What mass of copper is deposited from a Cu^2+ solution by a current of 0.500 A flowing for 965 s? (Molar mass of Cu = 63.55 g/mol)
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Correct: (B)
Q = 482.5 C = 0.00500 mol e−; mol Cu = 0.00250, mass = 0.00250 · 63.55 = 0.159 g.
☢ Nuclear & Descriptive Chemistry
Q59A ^218Po nucleus undergoes one alpha decay followed by two beta-minus decays. What is the resulting nuclide?
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Correct: (C)
Alpha decay: ^218Po → ^214Pb; two beta-minus decays raise Z by 2 with A unchanged: ^214Pb → ^214Bi → ^214Po.
Q60Which oxide forms an acidic aqueous solution?
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Correct: (A)
CO2 is a nonmetal oxide that reacts with water to form carbonic acid; the others are basic metal oxides.
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