AP Exam Prep · AP Chemistry

AP Chemistry Unit 3 Practice Test: Properties of Substances and Mixtures

Unit 3 has the largest exam weighting. It explains how forces between particles decide boiling points, gas behaviour and solubility, and how light is used to measure concentration.

Exam weighting:: 18–22%
Questions:: 13 multiple choice
Time:: about 17 minutes
Cost:: Free, no sign-up

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Question 1 of 13 · 0 answered

Topic 3.1 · Apply it

Hydrogen fluoride (HF) boils at 20 °C, while hydrogen chloride (HCl) boils at −85 °C. What best explains the difference?

HCl has more electrons, so it has stronger dispersion forces.The H–F covalent bond is stronger than the H–Cl bond.HCl molecules are nonpolar.HF molecules form hydrogen bonds with each other, which are stronger than the dipole–dipole forces between HCl molecules.

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Topic 3.13 · Data analysis

Absorbance of a dye solution measured in the same cuvette
Solution	Concentration (M)	Absorbance
Standard	0.020	0.40
Unknown	?	0.30

Using Beer's law, what is the concentration of the unknown?

0.027 M0.010 M0.015 M0.30 M

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What AP Chem Unit 3 covers

Unit 3, Properties of Substances and Mixtures, makes up 18–22% of the multiple-choice section and usually takes ~14–15 class periods. These are the topics in the current course framework, and every question in the test above is tagged with one of them.

3.1Intermolecular and Interparticle Forces
3.2Properties of Solids
3.3Solids, Liquids, and Gases
3.4Ideal Gas Law
3.5Kinetic Molecular Theory
3.6Deviation from Ideal Gas Law
3.7Solutions and Mixtures
3.8Representations of Solutions
3.9Separation of Solutions and Mixtures
3.10Solubility
3.11Spectroscopy and the Electromagnetic Spectrum
3.12Properties of Photons
3.13Beer-Lambert Law

Unit 3 key ideas

Intermolecular forces decide properties

Dispersion forces grow with the number of electrons; dipole–dipole forces need polar molecules; hydrogen bonding needs H bonded to N, O or F. Stronger forces mean higher boiling points.

Gases follow PV = nRT

Use kelvin, consistent units and R = 0.08206 L·atm·mol⁻¹·K⁻¹. Kinetic molecular theory says average kinetic energy depends only on temperature; real gases deviate at high pressure and low temperature.

Solutions and separations

Molarity is moles of solute per litre of solution. Like dissolves like, and chromatography and distillation separate mixtures by differences in intermolecular forces.

Light and concentration

E = hν = hc/λ links photon energy to wavelength. Different regions of the spectrum cause different transitions, and Beer–Lambert (A = εbc) relates absorbance to concentration.

Common Unit 3 mistakes

Using Celsius instead of kelvin in gas law calculations.
Saying hydrogen bonds are covalent bonds within a molecule.
Using millilitres instead of litres when calculating molarity.

How to study this unit

Rank substances by IMFs by first asking: does it hydrogen bond, is it polar, how many electrons does it have?
Convert all units before substituting into PV = nRT or A = εbc.

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About these questions

StudyCoach wrote these questions for this test. Each one is mapped to a topic in the College Board's current AP Chemistry course framework. Every answer key was also checked by a separate AI review, and any disagreement was rechecked by hand. They have not yet been reviewed by an AP Chemistry teacher. If you think an answer is wrong, email support@studycoach.io.

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