---
title: "AP Chemistry Unit 1 Practice Test"
description: "A timed AP Chemistry Unit 1 (Atomic Structure & Properties) practice test in the AP format, drawn from 1,589 multiple-choice questions and 55 FRQs written for the unit. The standard version takes about 60 minutes."
canonical: "https://fiveable.me/ap-chem/unit-test/1"
type: "unit-test"
subject: "AP Chemistry"
unit: "Unit 1"
---

# AP Chemistry Unit 1 Practice Test

## Overview

A timed AP Chemistry Unit 1 (Atomic Structure & Properties) practice test in the AP format, drawn from 1,589 multiple-choice questions and 55 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=1): 6 questions
- [FRQ 2 – Long Answer](/ap-chem/frqs/frq-2?unit=1): 5 questions
- [FRQ 3 – Long Answer](/ap-chem/frqs/frq-3?unit=1): 3 questions
- [FRQ 4 – Short Answer](/ap-chem/frqs/frq-4?unit=1): 11 questions
- [FRQ 5 – Short Answer](/ap-chem/frqs/frq-5?unit=1): 9 questions
- [FRQ 6 – Short Answer](/ap-chem/frqs/frq-6?unit=1): 9 questions
- [FRQ 7 – Short Answer](/ap-chem/frqs/frq-7?unit=1): 12 questions

## Practice Questions

### Question 1

A particulate model of a binary mixture shows 10 atoms of Element X (atomic mass 20 amu) and 10 atoms of Element Y (atomic mass 80 amu) distributed uniformly. What is the mass percent of Element X in this mixture?

- (A) 20%
- (B) 25%
- (C) 50%
- (D) 80%

**Answer: (A)** Calculating mass percent requires determining the total mass of each component. With 10 atoms of X (10 × 20 = 200 amu) and 10 atoms of Y (10 × 80 = 800 amu), the total mass is 1000 amu. The mass percent of X is (200/1000) × 100 = 20%.

### Question 2

A particulate diagram of a gas mixture in a sealed vessel shows 3 molecules of helium ($$He$$) and 1 molecule of neon ($$Ne$$). Based on the particle counts, what is the mole fraction of helium in the mixture?

- (A) 0.25
- (B) 0.33
- (C) 0.75
- (D) 3.00

**Answer: (C)** Determining mole fraction involves dividing the number of particles of the component by the total number of particles. With 3 He molecules and 1 Ne molecule (Total = 4), the fraction is 3/4 = 0.75.

### Question 3

A particulate representation of a reaction vessel initially contains 6 molecules of hydrogen ($$H_2$$) and 2 molecules of oxygen ($$O_2$$). The reaction $$2H_2 + O_2 \rightarrow 2H_2O$$ proceeds to completion. Which species remains unreacted and in what quantity?

- (A) 2 molecules of $$H_2$$
- (B) 2 molecules of $$O_2$$
- (C) 4 molecules of $$H_2$$
- (D) 4 molecules of $$O_2$$

**Answer: (A)** Stoichiometry dictates that 2 molecules of $$O_2$$ react with 4 molecules of $$H_2$$ (1:2 ratio). Starting with 6 $$H_2$$, subtracting the 4 consumed leaves 2 molecules of $$H_2$$ unreacted.

### Question 4

A particulate model of an aqueous solution depicts 4 formula units of potassium sulfate ($$K_2SO_4$$) fully dissociated into ions. What is the total count of potassium ions ($$K^+$$) and sulfate ions ($$SO_4^{2-}$$) represented in this model?

- (A) 4 potassium ions and 4 sulfate ions
- (B) 4 potassium ions and 8 sulfate ions
- (C) 8 potassium ions and 4 sulfate ions
- (D) 8 potassium ions and 8 sulfate ions

**Answer: (C)** Dissociation of 1 unit of $$K_2SO_4$$ yields 2 $$K^+$$ ions and 1 $$SO_4^{2-}$$ ion. Therefore, 4 units yield $$4 \times 2 = 8$$ potassium ions and $$4 \times 1 = 4$$ sulfate ions.

### Question 5

A sample of neon gas contains 9 atoms of $$^{20}Ne$$ (mass 20 amu) and 1 atom of $$^{22}Ne$$ (mass 22 amu). What is the average atomic mass of the neon in this sample, based strictly on the particles counted?

- (A) 20.0 amu
- (B) 20.2 amu
- (C) 21.0 amu
- (D) 22.0 amu

**Answer: (B)** Calculating the weighted average involves summing the total mass and dividing by the number of particles. Total mass = $$(9 \times 20) + (1 \times 22) = 202$$ amu. Average = $$202 / 10 = 20.2$$ amu.

### Question 6

A particulate model represents a sample of a compound where every molecule consists of 2 atoms of nitrogen and 4 atoms of oxygen. What is the empirical formula of the compound represented by this model?

- (A) $$NO_2$$
- (B) $$N_2O$$
- (C) $$N_2O_4$$
- (D) $$N_4O_2$$

**Answer: (A)** The empirical formula represents the simplest whole-number ratio of atoms. The molecular ratio of 2 nitrogen to 4 oxygen simplifies to 1:2, resulting in $$NO_2$$.

### Question 7

A 2.00 g impure sample containing $$CaCl_2$$ is dissolved and treated with excess $$AgNO_3$$, yielding 3.50 g of $$AgCl(s)$$. Which mathematical relationship should be used to determine the mass of $$CaCl_2$$ in the original sample?

- (A) $$Mass_{CaCl_2} = Mass_{AgCl} \times \frac{MM_{CaCl_2}}{2 \times MM_{AgCl}}$$
- (B) $$Mass_{CaCl_2} = Mass_{AgCl} \times \frac{MM_{AgCl}}{2 \times MM_{CaCl_2}}$$
- (C) $$Mass_{CaCl_2} = Mass_{AgCl} \times \frac{2 \times MM_{AgCl}}{MM_{CaCl_2}}$$
- (D) $$Mass_{CaCl_2} = Mass_{AgCl} \times \frac{MM_{CaCl_2}}{MM_{AgCl}}$$

**Answer: (A)** Connecting the stoichiometry of the precipitation reaction to the mass calculation.

### Question 8

A mixture of graphite ($$C$$) and inert ash is burned completely, producing $$CO_2$$. Which expression calculates the mass of carbon in the mixture based on the mass of $$CO_2$$ collected?

- (A) $$Mass_C = Mass_{CO_2} \times \frac{12.01 \text{ g}}{44.01 \text{ g}}$$
- (B) $$Mass_C = Mass_{CO_2} \times \frac{44.01 \text{ g}}{12.01 \text{ g}}$$
- (C) $$Mass_C = Mass_{CO_2} \times \frac{12.01 \text{ g}}{32.00 \text{ g}}$$
- (D) $$Mass_C = Mass_{CO_2} \times \frac{32.00 \text{ g}}{44.01 \text{ g}}$$

**Answer: (A)** Relating the mass of the element to the mass of the compound using molar masses.

### Question 9

A 1.00 g mixture contains only $$NaCl$$ and $$KCl$$. The total number of moles of chloride ions ($$n_{Cl^-}$$) is determined experimentally. Which system of equations allows for the calculation of the mass of $$NaCl$$ ($$x$$) and $$KCl$$ ($$y$$)?

- (A) $$x + y = 1.00$$ and $$\frac{x}{58.44} + \frac{y}{74.55} = n_{Cl^-}$$
- (B) $$x + y = 1.00$$ and $$\frac{x}{35.45} + \frac{y}{35.45} = n_{Cl^-}$$
- (C) $$x + y = n_{Cl^-}$$ and $$x(58.44) + y(74.55) = 1.00$$
- (D) $$\frac{x}{58.44} = \frac{y}{74.55}$$ and $$x + y = 1.00$$

**Answer: (A)** Establishing a system based on mass conservation and total moles of chloride.

### Question 10

A sample of hydrated copper(II) sulfate, $$CuSO_4 \cdot xH_2O$$, is heated until all water is lost. Which relationship correctly determines the value of $$x$$?

- (A) $$x = \frac{\text{moles of water lost}}{\text{moles of anhydrous } CuSO_4}$$
- (B) $$x = \frac{\text{mass of water lost}}{\text{mass of anhydrous } CuSO_4}$$
- (C) $$x = \frac{\text{moles of anhydrous } CuSO_4}{\text{moles of water lost}}$$
- (D) $$x = \frac{\text{mass of anhydrous } CuSO_4}{\text{mass of water lost}}$$

**Answer: (A)** Defining the coefficient x as the mole ratio of water to anhydrous salt.

## Review the Unit

- [1.1 Moles and Molar Mass](/ap-chem/unit-1/moles-molar-mass/study-guide/U0wdfzbGXdkv2l1LVdqP)
- [1.2 Mass Spectra of Elements](/ap-chem/unit-1/mass-spectroscopy-elements/study-guide/B4IVhweYImJO0nU86Kq7)
- [1.3 Elemental Composition of Pure Substances](/ap-chem/unit-1/elemental-composition-pure-substances/study-guide/EKrsYbL2G7PpzhUXDOSz)
- [1.4 Composition of Mixtures](/ap-chem/unit-1/composition-mixtures/study-guide/dKotYK10xJPuFb5FD15l)
- [1.5 Atomic Structure and Electron Configuration](/ap-chem/unit-1/atomic-structure-electron-configurations/study-guide/DiW6kVmwDRDakxKodjw5)
- [1.6 Photoelectron Spectroscopy](/ap-chem/unit-1/photoelectron-spectroscopy/study-guide/Xx7nwanr96Uzt1zSvwRA)
- [1.7 Periodic Trends](/ap-chem/unit-1/periodic-trends/study-guide/J1NnoL1NHgd6B1dG2UZe)
- [1.8 Valence Electrons and Ionic Compounds](/ap-chem/unit-1/valence-electrons-ionic-compounds/study-guide/XTtinEfGPR0jEJmpUuBx)

## Other Unit Tests

- [Unit 2: Compound Structure and Properties](/ap-chem/unit-test/2)
- [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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