AP Chemistry Practice Quiz: Moles and Molar Mass

Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026

Test your understanding with short quizzes. This quiz has 10 questions to check your progress.

Question 1 of 10

Which of the following best describes the role of Avogadro's number (6.022 x 10^23 mol⁻¹)?

A)It links the number of moles of a substance to the number of constituent particles.B)It represents the mass of one mole of a substance in grams.C)It is the number of grams in one atomic mass unit (amu).D)It connects the mass of a substance directly to its volume.

All Questions (10)

Which of the following best describes the role of Avogadro's number (6.022 x 10^23 mol⁻¹)?

A) It links the number of moles of a substance to the number of constituent particles.

B) It represents the mass of one mole of a substance in grams.

C) It is the number of grams in one atomic mass unit (amu).

D) It connects the mass of a substance directly to its volume.

Correct Answer: A

Based on the provided content, "Avogadro's number (NA = 6.022 x 10^23 mol⁻¹) links the number of moles in a pure sample to the number of constituent particles (or formula units)." This number serves as the conversion factor between the macroscopic scale (moles) and the microscopic scale (particles).

In a laboratory setting, why is it essential to use the mole concept to connect the mass of a substance to the number of particles?

A) Because the mass of a substance in grams is always equal to the number of particles.

B) Because particles are too small and numerous to be counted directly.

C) Because Avogadro's number changes depending on the substance.

D) Because dimensional analysis only works with moles, not with mass.

Correct Answer: B

The content states that there is a need for a connection between mass and particle number because "particles cannot be counted directly in the lab." The mole concept, along with molar mass and Avogadro's number, provides this essential link.

How many formula units are present in a 2.0 mole sample of a pure substance?

A) 6.022 x 10^23

B) 3.011 x 10^23

C) 1.204 x 10^24

D) 2.0

Correct Answer: C

To find the number of particles, multiply the number of moles by Avogadro's number. The calculation is: 2.0 mol × (6.022 x 10^23 particles/mol) = 1.2044 x 10^24 particles. This uses the principle that Avogadro's number links moles to particles.

A student measures a 90.0 g sample of a substance with a molar mass (M) of 180.0 g/mol. How many moles (n) of the substance are in the sample?

A) 2.00 moles

B) 1.00 mole

C) 0.500 moles

D) 16200 moles

Correct Answer: C

Using the formula n = m/M, where m is the mass and M is the molar mass. The calculation is: n = 90.0 g / 180.0 g/mol = 0.500 moles. This demonstrates the quantitative connection between mass and moles.

A sample is found to contain 3.011 x 10^23 constituent particles. How many moles of the substance are in this sample?

A) 0.5000 moles

B) 1.000 mole

C) 2.000 moles

D) 1.813 x 10^47 moles

Correct Answer: A

To find the number of moles from the number of particles, divide the number of particles by Avogadro's number using dimensional analysis. The calculation is: (3.011 x 10^23 particles) / (6.022 x 10^23 particles/mol) = 0.5000 moles.

What is the mass (m) of a 3.0 mole sample of a substance that has a molar mass (M) of 40.0 g/mol?

A) 13.3 g

B) 40.0 g

C) 43.0 g

D) 120 g

Correct Answer: D

To find the mass from moles, rearrange the formula n = m/M to solve for mass: m = n × M. The calculation is: m = 3.0 mol × 40.0 g/mol = 120 g.

A pure sample of a compound has a mass of 58.5 g and a molar mass of 58.5 g/mol. Approximately how many formula units are in the sample?

A) 1.0

B) 58.5

C) 6.022 x 10^23

D) 3.43 x 10^25

Correct Answer: C

This is a two-step calculation using dimensional analysis. First, find the number of moles using n = m/M: n = 58.5 g / 58.5 g/mol = 1.00 mol. Second, convert moles to particles using Avogadro's number: 1.00 mol × (6.022 x 10^23 particles/mol) = 6.022 x 10^23 particles.

The average mass of a single atom of an element is 12.01 amu. Based on the quantitative connection between particle mass and molar mass, what is the mass of one mole of these atoms?

A) 12.01 amu

B) 12.01 g

C) (12.01 / 6.022 x 10^23) g

D) (12.01 × 6.022 x 10^23) g

Correct Answer: B

The content states that "The average mass in amu of one particle is numerically equal to the molar mass of that substance in grams." Therefore, if one atom has an average mass of 12.01 amu, one mole of those atoms has a molar mass of 12.01 g/mol, meaning its mass is 12.01 grams.

A student has 10.0 g samples of four different pure substances. Which sample contains the greatest number of constituent particles? Substance A: Molar Mass = 20.0 g/mol Substance B: Molar Mass = 40.0 g/mol Substance C: Molar Mass = 60.0 g/mol Substance D: Molar Mass = 80.0 g/mol

A) Substance A

B) Substance B

C) Substance C

D) All samples contain the same number of particles.

Correct Answer: A

The number of particles is directly proportional to the number of moles (n). Since the mass (m) is the same for all samples (10.0 g), the number of moles is determined by the formula n = m/M. The substance with the smallest molar mass (M) will have the largest number of moles and therefore the greatest number of particles. Substance A has the lowest molar mass (20.0 g/mol), so it will contain the most moles and the most particles.

A chemist wants to calculate the number of particles in a 25.0 g sample of a substance with a molar mass of 50.0 g/mol. Which dimensional analysis setup correctly calculates the number of particles?

A) 25.0 g × (50.0 g / 1 mol) × (6.022 x 10^23 particles / 1 mol)

B) 25.0 g × (1 mol / 50.0 g) × (1 mol / 6.022 x 10^23 particles)

C) 25.0 g × (1 mol / 50.0 g) × (6.022 x 10^23 particles / 1 mol)

D) 25.0 g × (1 mol / 6.022 x 10^23 particles) × (50.0 g / 1 mol)

Correct Answer: C

The correct dimensional analysis setup must cancel units sequentially to result in 'particles'. In option C, grams cancel first (g × mol/g), and then moles cancel (mol × particles/mol), leaving the desired unit of particles. The first step (1 mol / 50.0 g) correctly converts mass to moles, and the second step (6.022 x 10^23 particles / 1 mol) correctly converts moles to particles.