AP Chemistry Unit 2 practice questions
Try 10 multiple-choice questions from Unit 2 here. Pick an answer to see why it's right or wrong, then take the timed test above for a full AP-style set.
Question 1
A student determines the density of a pure aluminum sample to analyze the packing efficiency of its metallic bonding lattice. The student uses the water displacement method but fails to remove several large air bubbles adhering to the metal sample when measuring its volume. How does this error affect the calculated density and the evaluation of the metallic packing?
The measured volume will be too high, causing the calculated density to be too low and the packing efficiency to be underestimated.
The measured volume will be too high, causing the calculated density to be too high and the packing efficiency to be overestimated.
The measured volume will be too low, causing the calculated density to be too low and the packing efficiency to be underestimated.
The measured volume will be too high, causing the calculated density to be too low, but the packing efficiency will remain accurate because the mass is unchanged.
Show answer
Answer: (A)
Connecting the volume measurement error to the density formula (D = m/V) explains the result. The air bubbles add to the displaced volume without adding mass, inflating the denominator and reducing the calculated density, which implies a less efficient packing of atoms than exists in reality.
Question 2
A particulate model of an alloy shows copper atoms (radius 128 pm) and zinc atoms (radius 134 pm) arranged in a crystal lattice. Which claim about the structure of this alloy is best supported by the atomic radii?
It forms a substitutional alloy because the copper and zinc atoms have similar radii.
It forms an interstitial alloy because the copper and zinc atoms have similar radii.
It forms a substitutional alloy because the copper and zinc atoms have very different radii.
It forms an interstitial alloy because the copper and zinc atoms have very different radii.
Show answer
Answer: (A)
Connecting atomic size data to alloy structure reveals that atoms of similar radii (128 pm and 134 pm) can replace each other in the crystal lattice. This substitution mechanism characterizes substitutional alloys, distinguishing them from interstitial alloys where smaller atoms fill spaces between larger ones.
Question 3
A student models a mole sample of copper(II) sulfate pentahydrate () as a mixture containing mole of solid and moles of liquid water. Which statement best describes the limitation of this model in connecting particulate structure to macroscopic behavior?
It fails because the water molecules are chemically integrated into the crystal lattice, not liquid.
It fails because the copper sulfate ions are dissolved in the water molecules, not solid particles.
It succeeds because the total mass is the sum of the anhydrous salt and the water components.
It succeeds because the water molecules are loosely attached to the surface of the solid crystal.
Show answer
Answer: (A)
Evaluating the model against particulate reality shows that hydrates contain water molecules in specific positions within the solid structure, not as a separate liquid phase.
Question 4
A student models a substitutional alloy of gold () and copper () by replacing of the gold atoms in a pure gold lattice with copper atoms. The student predicts the density will decrease. Which statement best evaluates this prediction based on the particulate model?
It is correct because the mass of a copper atom is significantly less than the mass of a gold atom.
It is correct because the volume of a copper atom is significantly greater than that of a gold atom.
It is incorrect because the total number of atoms in the crystal lattice remains exactly the same.
It is incorrect because the smaller volume of copper atoms leads to a contraction of the lattice.
Show answer
Answer: (A)
Connecting particulate properties to density () shows that replacing heavy atoms ( amu) with lighter atoms ( amu) reduces the total mass significantly.
Question 5
A student creates a particulate model of solid potassium chloride () showing discrete diatomic molecules containing one potassium ion and one chloride ion. Which of the following best explains why this model is inconsistent with the chemical nature of the substance?
Inconsistent, because ionic compounds form extended crystal lattices
Consistent, because it shows the correct 1:1 ratio of ions in the unit
Inconsistent, because potassium and chloride form covalent bonds
Consistent, because the formula unit represents a distinct molecule
Show answer
Answer: (A)
Potassium chloride is an ionic compound composed of a continuous 3D network of ions, not discrete molecular units. The formula represents the simplest ratio (formula unit), not a distinct molecule.
Question 6
A student proposes a model for solid silicon dioxide () consisting of individual molecules held together by weak intermolecular forces. Which statement correctly evaluates this model based on the properties of silicon dioxide?
Inconsistent, because forms a covalent network solid
Consistent, because has a simple molecular structure
Inconsistent, because is an ionic compound with a lattice
Consistent, because silicon and oxygen form double bonds
Show answer
Answer: (A)
Silicon dioxide exists as a covalent network solid (like diamond or quartz) where every silicon atom is bonded to four oxygen atoms in a continuous grid, not as discrete molecules.
Question 7
A particulate model shows 3 formula units of magnesium chloride () dissolved completely in water. How many total ions should be depicted in the solution phase of this model?
3 ions
6 ions
9 ions
12 ions
Show answer
Answer: (C)
Each unit dissociates into 1 and 2 ions (3 ions total). 3 units 3 ions/unit = 9 total ions.
Question 8
Heating a blue copper sulfate sample causes a 36% mass loss and a color change to white. A student claims the original solid was a hydrate. Which justification best connects the macroscopic mass loss to the particulate structure?
The mass loss results from the release of discrete water molecules bound within the crystal lattice.
The mass loss results from the release of oxygen gas molecules bound within the crystal lattice.
The mass loss results from the release of copper ions located within the crystal lattice.
The mass loss results from the release of sulfate ions located within the crystal lattice.
Show answer
Answer: (A)
Connecting macroscopic mass change to particulate structure. Hydrates contain specific ratios of water molecules integrated into the ionic lattice; heating releases these molecules as gas, causing the observed mass decrease.
Question 9
Zinc(II) solutions are typically colorless, unlike many other transition metal solutions. A student argues that the ion's electron configuration explains this macroscopic property. Which statement best supports this argument?
The argument is valid because the filled 3d subshell prevents electron transitions between d-orbitals that absorb visible light.
The argument is valid because the empty 4s subshell prevents electron transitions between s-orbitals that absorb visible light.
The argument is invalid because the filled 3d subshell should cause strong absorption of visible light due to electron density.
The argument is invalid because the empty 4s subshell should cause strong absorption of visible light due to electron vacancies.
Show answer
Answer: (A)
Connects the microscopic configuration to the macroscopic property of color. Color in transition metals usually arises from d-d transitions; a completely filled d-subshell () makes these transitions impossible.
Question 10
A student measures the melting point of to investigate lattice energy. If the student modifies the procedure by using instead, how will the measured melting point differ?
The melting point will be higher because the fluoride ion is smaller than the chloride ion, resulting in stronger Coulombic attraction.
The melting point will be lower because the fluoride ion is more electronegative, causing the ionic bonds to become more polar and weak.
The melting point will be higher because the fluoride ion has a higher electron affinity, making the lattice more stable against heat.
The melting point will be lower because the fluoride ion has fewer electrons, resulting in weaker London dispersion forces.
Show answer
Answer: (A)
Lattice energy is proportional to . Since has a smaller ionic radius than (with the same charge), the internuclear distance is smaller, making the electrostatic attraction and melting point higher.
What's on the AP Chemistry Unit 2 practice test
The standard version takes about 60 minutes and follows the timing and directions of the AP exam, sized to one unit:
- 20 Multiple Choice Questions (30 minutes)
- 1 FRQ – FRQ 1 – Long Answer (15 minutes)
- 1 FRQ – FRQ 4 – Short Answer (15 minutes)
Questions are drawn from 1120 multiple-choice questions and 38 FRQs written for Unit 2, Compound Structure and Properties.
Practice AP Chemistry Unit 2 FRQs
Answer the unit's free-response questions one at a time and get a score on every part.
- FRQ 1 – Long Answer (9 questions)
- FRQ 2 – Long Answer (9 questions)
- FRQ 3 – Long Answer (3 questions)
- FRQ 4 – Short Answer (4 questions)
- FRQ 5 – Short Answer (2 questions)
- FRQ 6 – Short Answer (7 questions)
- FRQ 7 – Short Answer (4 questions)
Review Unit 2 before you start
- 2.1 Types of Chemical Bonds
- 2.2 Intramolecular Force and Potential Energy
- 2.3 Structure of Ionic Solids
- 2.4 Structure of Metals and Alloys
- 2.5 Lewis Diagrams
- 2.6 Resonance and Formal Charge
- 2.7 VSEPR and Bond Hybridization