---
title: "AP Chemistry Unit 2 Practice Test"
description: "A timed AP Chemistry Unit 2 (Compound Structure and Properties) practice test in the AP format, drawn from 1,120 multiple-choice questions and 38 FRQs written for the unit. The standard version takes about 60 minutes."
canonical: "https://fiveable.me/ap-chem/unit-test/2"
type: "unit-test"
subject: "AP Chemistry"
unit: "Unit 2"
---

# AP Chemistry Unit 2 Practice Test

## Overview

A timed AP Chemistry Unit 2 (Compound Structure and Properties) practice test in the AP format, drawn from 1,120 multiple-choice questions and 38 FRQs written for the unit. The standard version takes about 60 minutes.

## Test Format

- 20 Multiple Choice Questions (30 minutes)
- 1 FRQ – FRQ 1 – Long Answer (15 minutes)
- 1 FRQ – FRQ 4 – Short Answer (15 minutes)

## Unit FRQs by Type

- [FRQ 1 – Long Answer](/ap-chem/frqs/frq-1?unit=2): 9 questions
- [FRQ 2 – Long Answer](/ap-chem/frqs/frq-2?unit=2): 9 questions
- [FRQ 3 – Long Answer](/ap-chem/frqs/frq-3?unit=2): 3 questions
- [FRQ 4 – Short Answer](/ap-chem/frqs/frq-4?unit=2): 4 questions
- [FRQ 5 – Short Answer](/ap-chem/frqs/frq-5?unit=2): 2 questions
- [FRQ 6 – Short Answer](/ap-chem/frqs/frq-6?unit=2): 7 questions
- [FRQ 7 – Short Answer](/ap-chem/frqs/frq-7?unit=2): 4 questions

## Practice Questions

### 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?

- (A) The measured volume will be too high, causing the calculated density to be too low and the packing efficiency to be underestimated.
- (B) The measured volume will be too high, causing the calculated density to be too high and the packing efficiency to be overestimated.
- (C) The measured volume will be too low, causing the calculated density to be too low and the packing efficiency to be underestimated.
- (D) 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.

**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 jeweler claims that an alloy composed of $$Au$$ (density $$19.3\text{ g/cm}^3$$) and $$Ag$$ (density $$10.5\text{ g/cm}^3$$) is greater than $$90\%$$ gold by mass. The measured density of the alloy is $$12.0\text{ g/cm}^3$$. Which reasoning best justifies rejecting this claim based on particulate composition?

- (A) The density is closer to pure $$Ag$$, implying $$Ag$$ atoms constitute the majority of the mass.
- (B) The density is closer to pure $$Au$$, implying $$Au$$ atoms constitute the majority of the mass.
- (C) The density is intermediate, implying equal numbers of $$Au$$ and $$Ag$$ atoms in the lattice.
- (D) The density is lower than pure $$Au$$, implying $$Ag$$ atoms are denser than $$Au$$ atoms.

**Answer: (A)** Comparing the measured density to the pure densities reveals the composition. A density of $$12.0\text{ g/cm}^3$$ is much closer to $$Ag$$ ($$10.5$$) than $$Au$$ ($$19.3$$), indicating the alloy is mostly silver, refuting the $$90\%$$ gold claim.

### Question 3

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?

- (A) It forms a substitutional alloy because the copper and zinc atoms have similar radii.
- (B) It forms an interstitial alloy because the copper and zinc atoms have similar radii.
- (C) It forms a substitutional alloy because the copper and zinc atoms have very different radii.
- (D) It forms an interstitial alloy because the copper and zinc atoms have very different radii.

**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 4

A student compares a particulate model of pure gold to a model of a gold-copper alloy. The alloy model shows copper atoms replacing some gold atoms in the crystal lattice without changing the unit cell volume. Given that copper atoms ($$63.55$$ g/mol) are lighter than gold atoms ($$196.97$$ g/mol), which observation about the alloy's density is correct?

- (A) The density of the alloy is lower than pure gold because mass decreases while volume is constant.
- (B) The density of the alloy is higher than pure gold because mass increases while volume is constant.
- (C) The density of the alloy is the same as pure gold because the atomic arrangement remains fixed.
- (D) The density of the alloy is variable because the copper atoms move freely within the lattice.

**Answer: (A)** In a substitutional alloy where lighter atoms replace heavier ones without changing volume, the total mass of the unit cell decreases, leading to a lower density.

### Question 5

In a substitutional alloy model, 25% of the gold ($Au$) atoms in the lattice are replaced by copper ($Cu$) atoms. Which statement best explains the resulting elemental composition by mass?

- (A) The mass percent of gold is greater than 75% because gold atoms are more massive than copper atoms.
- (B) The mass percent of gold is greater than 75% because gold atoms are larger in radius than copper atoms.
- (C) The mass percent of gold is equal to 75% because the ratio of gold atoms to total atoms is exactly 3 to 4.
- (D) The mass percent of gold is less than 75% because gold atoms are more massive than copper atoms.

**Answer: (A)** Connecting the atomic masses to the alloy composition reveals that since gold (~197 amu) is much heavier than copper (~63.5 amu), the 75% of atoms that are gold contribute significantly more than 75% of the total mass.

### Question 6

A sample of iron(II) oxide is analyzed and found to have 75.0% iron by mass, while the ideal particulate model $$FeO$$ predicts 77.7% iron. Which statement best describes the degree to which the ideal $$FeO$$ model represents the actual sample?

- (A) The model fails to represent the sample because the actual lattice contains iron vacancies
- (B) The model fails to represent the sample because the actual lattice contains oxygen vacancies
- (C) The model accurately represents the sample because the discrepancy is due to experimental error
- (D) The model accurately represents the sample because the ratio of atoms must be a whole number

**Answer: (A)** Analyzing the data shows the experimental iron percentage is lower than predicted (75.0% < 77.7%), indicating the presence of vacancies where iron atoms are missing from the lattice.

### Question 7

A student proposes a particulate model consisting of alternating gold ($$Au$$) and silver ($$Ag$$) atoms in a 1:1 ratio to represent an alloy used in jewelry. Analysis shows the alloy's composition varies between samples. Which statement best evaluates the model's ability to describe this macroscopic property?

- (A) The model is ineffective because it implies a constant composition not observed
- (B) The model is ineffective because it implies a variable composition not observed
- (C) The model is effective because it shows the metallic bonding between the atoms
- (D) The model is effective because it shows the fixed integer ratio of the atoms

**Answer: (A)** Critiquing the model reveals that a fixed 1:1 atomic arrangement represents a compound with definite proportions, failing to account for the variable composition characteristic of mixtures.

### Question 8

A student models a $$1.0$$ mole sample of copper(II) sulfate pentahydrate ($$CuSO_4 \cdot 5H_2O$$) as a mixture containing $$1$$ mole of $$CuSO_4$$ solid and $$5$$ moles of liquid water. Which statement best describes the limitation of this model in connecting particulate structure to macroscopic behavior?

- (A) It fails because the water molecules are chemically integrated into the crystal lattice, not liquid.
- (B) It fails because the copper sulfate ions are dissolved in the water molecules, not solid particles.
- (C) It succeeds because the total mass is the sum of the anhydrous salt and the water components.
- (D) It succeeds because the water molecules are loosely attached to the surface of the solid crystal.

**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 9

A student models a substitutional alloy of gold ($$Au$$) and copper ($$Cu$$) by replacing $$50\%$$ 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?

- (A) It is correct because the mass of a copper atom is significantly less than the mass of a gold atom.
- (B) It is correct because the volume of a copper atom is significantly greater than that of a gold atom.
- (C) It is incorrect because the total number of atoms in the crystal lattice remains exactly the same.
- (D) It is incorrect because the smaller volume of copper atoms leads to a contraction of the lattice.

**Answer: (A)** Connecting particulate properties to density ($$m/V$$) shows that replacing heavy $$Au$$ atoms ($$197$$ amu) with lighter $$Cu$$ atoms ($$63.5$$ amu) reduces the total mass significantly.

### Question 10

A student creates a particulate model of solid potassium chloride ($$KCl$$) 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?

- (A) Inconsistent, because ionic compounds form extended crystal lattices
- (B) Consistent, because it shows the correct 1:1 ratio of ions in the unit
- (C) Inconsistent, because potassium and chloride form covalent bonds
- (D) Consistent, because the formula unit represents a distinct molecule

**Answer: (A)** Potassium chloride is an ionic compound composed of a continuous 3D network of ions, not discrete molecular units. The formula $$KCl$$ represents the simplest ratio (formula unit), not a distinct molecule.

## Review the Unit

- [2.1 Types of Chemical Bonds](/ap-chem/unit-2/types-chemical-bonds/study-guide/syV9vHl1BKGwM5tnaOt0)
- [2.2 Intramolecular Force and Potential Energy ](/ap-chem/unit-2/intramolecular-force-potential-energy/study-guide/2ybBItwMrCkB9MAOO9lC)
- [2.3 Structure of Ionic Solids](/ap-chem/unit-2/structure-ionic-solids/study-guide/3khaTI6A3tdnaMTMJy2u)
- [2.4 Structure of Metals and Alloys](/ap-chem/unit-2/structure-metals-alloys/study-guide/yTmM9j22ZoTxtr6TCC3p)
- [2.5 Lewis Diagrams](/ap-chem/unit-2/lewis-diagrams/study-guide/KjqTRYr5TVr2C3Be3u0J)
- [2.6 Resonance and Formal Charge](/ap-chem/unit-2/resonance-formal-charge/study-guide/rxtiCdBiDF6V9V7S2UEi)
- [2.7 VSEPR and Bond Hybridization](/ap-chem/unit-2/vsepr-bond-hybridization/study-guide/OslsAmh8LcVoqbpnjPAu)

## Other Unit Tests

- [Unit 1: Atomic Structure & Properties](/ap-chem/unit-test/1)
- [Unit 3: Properties of Substances and Mixtures](/ap-chem/unit-test/3)
- [Unit 4: Chemical Reactions](/ap-chem/unit-test/4)
- [Unit 5: Kinetics](/ap-chem/unit-test/5)
- [Unit 6: Thermochemistry](/ap-chem/unit-test/6)
- [Unit 7: Equilibrium](/ap-chem/unit-test/7)
- [Unit 8: Acids & Bases](/ap-chem/unit-test/8)
- [Unit 9: Thermodynamics and Electrochemistry](/ap-chem/unit-test/9)

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