AP® CHEMISTRY

Practice Questions

24 original exam-style questions with step-by-step explanations — covering every unit of the AP Chemistry curriculum.

24
Questions
9
Units
100%
Explained
Unit 1 Unit 2 Unit 3 Unit 4 Unit 5 Unit 6 Unit 7 Unit 8 Unit 9
💡 How to use: Read each question carefully, pick your answer, then tap Reveal Answer to check and learn from the explanation.
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UNIT 1

Atomic Structure and Properties

3 questions
1

Which of the following correctly orders the elements by increasing first ionization energy?

ANa < Mg < Al < Si
BAl < Si < Na < Mg
CNa < Al < Mg < Si
DSi < Mg < Al < Na
🔎 Reveal Answer
✓ Correct Answer: C
Ionization energy generally increases across a period (left to right) due to increasing effective nuclear charge. The order across period 3 is Na < Mg < Al < Si. Note that Al is slightly lower than Mg because Al’s outer electron is in a 3p orbital (higher energy, more shielded) while Mg’s is in 3s — but Mg is still lower than Si. The correct increasing order is Na < Al < Mg < Si.
2

An element has the electron configuration [Ar] 4s2 3d10 4p3. In which group and period is this element located?

AGroup 13, Period 4
BGroup 15, Period 4
CGroup 5, Period 4
DGroup 15, Period 5
🔎 Reveal Answer
✓ Correct Answer: B
The highest principal quantum number is 4, so the element is in Period 4. The valence electrons are 4s2 4p3 = 5 valence electrons, placing it in Group 15. This is arsenic (As).
3

The mass spectrum of an element shows peaks at m/z = 35 (75.8%) and m/z = 37 (24.2%). What is the average atomic mass?

A35.00 amu
B35.48 amu
C36.00 amu
D35.97 amu
🔎 Reveal Answer
✓ Correct Answer: B
Average atomic mass = (35 × 0.758) + (37 × 0.242) = 26.53 + 8.954 = 35.48 amu. This is chlorine.
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UNIT 2

Molecular and Ionic Compound Structure

3 questions
4

Which molecule has a trigonal pyramidal geometry?

ABF3
BNH3
CCO2
DCH4
🔎 Reveal Answer
✓ Correct Answer: B
NH3 has 3 bonding pairs and 1 lone pair on nitrogen (AX3E), giving trigonal pyramidal geometry. BF3 is trigonal planar, CO2 is linear, CH4 is tetrahedral.
5

Which of the following has the shortest bond length?

AC–C
BC=C
CC≡C
DC–H
🔎 Reveal Answer
✓ Correct Answer: C
Bond length decreases as bond order increases. A triple bond (C≡C) has the highest bond order (3) and therefore the shortest bond length among the carbon-carbon bonds listed.
6

Which compound has the highest lattice energy?

ANaCl
BMgO
CKCl
DCaS
🔎 Reveal Answer
✓ Correct Answer: B
Lattice energy increases with higher ionic charges and smaller ionic radii. MgO has 2+ and 2− ions (highest charges), and Mg2+ and O2− are smaller than Ca2+ and S2−, giving MgO the highest lattice energy.
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UNIT 3

Intermolecular Forces and Properties

2 questions
7

Which substance has the highest boiling point?

ACH4
BCH3CH3
CCH3OH
DCH3CH2CH3
🔎 Reveal Answer
✓ Correct Answer: C
CH3OH can form hydrogen bonds (O–H), the strongest intermolecular force among the options. The others only have London dispersion forces. Hydrogen bonding gives methanol a significantly higher boiling point (65°C) than the hydrocarbons.
8

A gas deviates most from ideal behavior under which conditions?

AHigh temperature, low pressure
BLow temperature, high pressure
CHigh temperature, high pressure
DLow temperature, low pressure
🔎 Reveal Answer
✓ Correct Answer: B
Real gases deviate from ideal behavior when intermolecular forces become significant (low temperature — particles move slowly and attract each other) and when particle volume is significant relative to container volume (high pressure — particles are forced close together).
🧪
UNIT 4

Chemical Reactions

3 questions
9

What is the oxidation number of chromium in K2Cr2O7?

A+3
B+6
C+7
D+12
🔎 Reveal Answer
✓ Correct Answer: B
K = +1 (×2 = +2), O = −2 (×7 = −14). Let Cr = x: 2 + 2x − 14 = 0 → 2x = 12 → x = +6.
10

When 4.0 g of H2 reacts with 32.0 g of O2, what is the maximum mass of H2O produced?

A18.0 g
B36.0 g
C32.0 g
D40.0 g
🔎 Reveal Answer
✓ Correct Answer: B
2H2 + O2 → 2H2O. Moles H2 = 4.0/2.0 = 2.0 mol. Moles O2 = 32.0/32.0 = 1.0 mol. The stoichiometric ratio is 2:1, so neither is limiting — both are consumed exactly. Moles H2O = 2.0 mol × 18.0 g/mol = 36.0 g.
11

Which net ionic equation represents the reaction between aqueous lead(II) nitrate and potassium iodide?

APb2+ + 2NO3− + 2K+ + 2I− → PbI2 + 2K+ + 2NO3−
BPb2+ + 2I− → PbI2(s)
CPb(NO3)2 + 2KI → PbI2 + 2KNO3
DK+ + NO3− → KNO3
🔎 Reveal Answer
✓ Correct Answer: B
PbI2 is the precipitate. Spectator ions (K+ and NO3−) are removed to give the net ionic equation: Pb2+(aq) + 2I−(aq) → PbI2(s).
⏱
UNIT 5

Kinetics

3 questions
12

For the reaction A → products, the rate law is rate = k[A]2. If [A] is doubled, the rate increases by a factor of:

A2
B4
C8
D1 (no change)
🔎 Reveal Answer
✓ Correct Answer: B
Second-order in A: rate ∝ [A]2. Doubling [A] gives (2)2 = 4 times the rate.
13

A catalyst increases the rate of a reaction by:

AIncreasing the activation energy
BProviding an alternate pathway with lower activation energy
CIncreasing the temperature
DShifting the equilibrium toward products
🔎 Reveal Answer
✓ Correct Answer: B
A catalyst provides an alternative reaction mechanism with a lower activation energy, increasing the fraction of molecules with sufficient energy to react. It does not change ΔH, temperature, or the equilibrium position.
14

The half-life of a first-order reaction is 30 minutes. What fraction of the reactant remains after 90 minutes?

A1/2
B1/4
C1/8
D1/16
🔎 Reveal Answer
✓ Correct Answer: C
90 minutes = 3 half-lives. After each half-life, half remains: (1/2)3 = 1/8.
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UNIT 6

Thermodynamics

2 questions
15

For a reaction with ΔH = −120 kJ/mol and ΔS = −150 J/(mol·K), at what temperature does the reaction become non-spontaneous?

ABelow 800 K
BAbove 800 K
CBelow 800°C
DThe reaction is always spontaneous
🔎 Reveal Answer
✓ Correct Answer: B
ΔG = ΔH − TΔS. Set ΔG = 0: T = ΔH/ΔS = (−120,000)/(−150) = 800 K. With ΔH < 0 and ΔS < 0, the reaction is spontaneous at low T and non-spontaneous at high T (above 800 K).
16

Which process has a positive ΔS?

AH2O(l) → H2O(s)
B2H2(g) + O2(g) → 2H2O(l)
CCaCO3(s) → CaO(s) + CO2(g)
DN2(g) + 3H2(g) → 2NH3(g)
🔎 Reveal Answer
✓ Correct Answer: C
Entropy increases when a gas is produced from a solid (more microstates, more disorder). In C, 1 mole of solid produces 1 mole of gas + 1 mole of solid — net increase in disorder. The others decrease moles of gas or go from liquid to solid.
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UNIT 7

Equilibrium

3 questions
17

For the reaction N2(g) + 3H2(g) ⇌ 2NH3(g), Kp = 4.5 × 10−5 at 500 K. What is the value of Kc?

A4.5 × 10−5
B1.8 × 10−3
C1.1 × 10−6
D7.6 × 10−2
🔎 Reveal Answer
✓ Correct Answer: D
Kp = Kc(RT)Δn, where Δn = 2 − 4 = −2. So Kc = Kp(RT)2 = (4.5 × 10−5)(0.08206 × 500)2 = (4.5 × 10−5)(41.03)2 = (4.5 × 10−5)(1683) ≈ 7.6 × 10−2.
18

For the exothermic reaction 2SO2(g) + O2(g) ⇌ 2SO3(g), which change will shift equilibrium toward products?

AIncreasing temperature
BDecreasing pressure
CAdding a catalyst
DDecreasing temperature
🔎 Reveal Answer
✓ Correct Answer: D
For an exothermic reaction (ΔH < 0), decreasing temperature shifts equilibrium toward products (Le Chatelier’s principle — the system counteracts the cooling by producing more heat via the forward reaction). A catalyst does not shift equilibrium.
19

The Ksp of AgCl is 1.8 × 10−10. What is the molar solubility of AgCl in water?

A1.8 × 10−10 M
B1.3 × 10−5 M
C3.6 × 10−10 M
D9.0 × 10−11 M
🔎 Reveal Answer
✓ Correct Answer: B
AgCl(s) ⇌ Ag+ + Cl−. If solubility = s, then Ksp = s2. s = √(1.8 × 10−10) = 1.34 × 10−5 M.
🧭
UNIT 8

Acids and Bases

3 questions
20

What is the pH of a 0.010 M solution of HClO4?

A1.00
B2.00
C4.00
D12.00
🔎 Reveal Answer
✓ Correct Answer: B
HClO4 is a strong acid, fully dissociated: [H+] = 0.010 M. pH = −log(0.010) = 2.00.
21

Which is the best buffer system?

AHCl / NaCl
BCH3COOH / CH3COONa
CNaOH / HCl
DH2SO4 / NaHSO4
🔎 Reveal Answer
✓ Correct Answer: B
A buffer requires a weak acid and its conjugate base (or weak base and conjugate acid). CH3COOH (weak acid) / CH3COO− (conjugate base) is the classic buffer. HCl is strong (A is wrong), NaOH/HCl neutralize (C is wrong), H2SO4 first proton is strong (D is poor).
22

In the titration of a weak acid with a strong base, the pH at the equivalence point is:

ALess than 7
BEqual to 7
CGreater than 7
DCannot be determined
🔎 Reveal Answer
✓ Correct Answer: C
At the equivalence point, all weak acid has been converted to its conjugate base, which hydrolyzes in water to produce OH−: A− + H2O ⇌ HA + OH−. This makes the solution basic (pH > 7).
🔋
UNIT 9

Applications of Thermodynamics (Electrochemistry)

2 questions
23

For a galvanic cell with E°cell = +1.10 V and n = 2, what is ΔG°?

A−212 kJ/mol
B+212 kJ/mol
C−106 kJ/mol
D+106 kJ/mol
🔎 Reveal Answer
✓ Correct Answer: A
ΔG° = −nFE° = −(2)(96,485)(1.10) = −212,267 J/mol ≈ −212 kJ/mol. Negative ΔG° confirms the cell reaction is spontaneous.
24

In an electrolytic cell, which statement is TRUE?

AThe anode is positive and oxidation occurs there
BThe anode is negative and oxidation occurs there
CThe cathode is positive and reduction occurs there
DElectrons flow from cathode to anode through the wire
🔎 Reveal Answer
✓ Correct Answer: B
In an electrolytic cell (non-spontaneous, driven by external power), the anode is connected to the positive terminal of the power supply but is labeled negative by convention (it supplies electrons). Oxidation always occurs at the anode (An Ox), reduction at the cathode (Red Cat). Electrons flow from anode to cathode through the external wire.

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