AP Chemistry Unit 3 Practice Test 2025 Properties of Substances and Mixtures

Last Updated on January 14, 2025

AP Chemistry Unit 3 Practice Test 2025 Properties of Substances and Mixtures. These are the sample questions and answers on the Unit 3: Properties of Substances and Mixtures AP Chemistry exam. You can try both Multiple Choice Questions and Answers and Free-Response Questions. This unit is 18–22% of the Advanced Placement (AP) Exam score.

These multiple-choice questions are about the Intermolecular forces, Solids, liquids, and gases, Kinetic molecular theory, Solutions, and mixtures.

Table of Contents

AP Chemistry Unit 3 Practice Test

AP Chemistry Unit 3: Properties of Substances and Mixtures

AP Chemistry Practice Test
Unit 3: Properties of Substances and Mixtures
Total Items: 18 (Multiple Choice Questions)

Unit 3: Properties of Substances and Mixtures

You’ll explore how atoms come together to create solids, liquids, and gases, and how forces between particles govern the properties of everything around you.

Topics may include:

Intermolecular forces
Solids, liquids, and gases
Kinetic molecular theory
Solutions and mixtures
Properties of photons
Spectroscopy

1 / 18

At STP a 5.00 L flask filled with air has a mass of 543.251 g. The air in the flask is replaced with another gas, and the mass of the flask is then determined to be 566.107 g. The density of air is 1.290 g L⁻¹. What is the gas that replaced the air?

(A) Ne

(B) O2

(D) Xe

2 / 18

Hydrogen gas can be prepared by the addition of hydrochloric acid to a sample of zinc. Upon completion of the reaction, 195 mL of gas were collected by water displacement at 25 °C and 753 torr. What mass of the hydrogen gas was collected? P_water = 24 torr at 25 °C.

(A) 0.00765 g

(B) 0.0154 g

(D) 0.159 g

3 / 18

At 30 °C a sample of hydrogen is collected over water (P_H2O = 31.82 mm Hg at 30 °C) in a 500 mL flask. The total pressure in the collection flask is 745 mm Hg. What will be the percent of error in the amount of hydrogen reported if the correction for the vapor pressure of water is not made?

(A) −4.5%

(B) 0.0%

(D) +4.5%

4 / 18

How many moles of helium are needed to fill a balloon that has a volume of 6.45 L and a pressure of 800 mm Hg at a room temperature of 24 °C? Assume ideal gas behavior.

(A) 0.278 moles

(B) 0.288 moles

(D) 2.65 × 103 moles

5 / 18

A gas will behave more like an ideal gas if we have a _________ and a(n) ______________.

(A) large volume, increased temperature

(B) high temperature, high average kinetic energy

(D) high effusion rate, high pressure

6 / 18

The kinetic molecular theory postulates a direct relationship between

(A) increased volume and increased average kinetic energy

(B) increased temperature and increased average kinetic energy

(D) increased effusion rate and increased pressure

7 / 18

The figure below represents the relative number of gas molecules in separate 2.0 L rigid containers of Cl₂, N₂, and Ne. The pressure of the container with Cl₂ is 6.0 atm. If all three gases are transferred to an evacuated 4.0 L rigid container at constant temperature, what would be the total pressure?

(A) 2.5 atm

(B) 5.0 atm

(D) 10. atm

8 / 18

What information does this graph contain?

(A) Few molecules have small kinetic energies.

(B) A small number of molecules have very large kinetic energies.

(D) All of the above.

9 / 18

Which of the following representations is best for communicating the idea about dynamic equilibrium and why?

(A) The representation on the left because liquid has to change into a gas to have an equilibrium

(B) The center representation since it shows gas molecules coming out of the water and some coming back in

(C) The representation on the right since there are exactly the same number of molecules condensing into the liquid as there are molecules evaporating

(D) None of these is correct because a dynamic equilibrium occurs only in aqueous solution and most often for weak acids and bases

10 / 18

Which of the following is a molecular representation of the physical property described as the surface tension of a liquid?

11 / 18

When a small beaker of ethanol boils on a hot plate, small bubbles form at the bottom of the beaker and rise to the surface. An inverted test tube full of ethanol is held in the boiling ethanol to catch the bubbles by displacement. Which of the following best describes the vapor that is captured?

(A) When the vapor is condensed, the liquid burns easily.

(B) When a burning match approaches the test tube, the gas explodes.

(D) All of the above.

12 / 18

On the basis of this heating curve, which of the following statements is correct about the substance?

(A) The substance supercools easily.

(B) The gas is a metastable state.

(D) The specific heat can be determined if the mass is known.

13 / 18

On the basis of this heating curve, which of the following statements is true?

(A) The heat of fusion is less than the heat of vaporization.

(B) The heat capacities of the solid, liquid, and gas are approximately equal.

(D) The heat capacity of the gas is greater than the heat of fusion.

14 / 18

What does this graph tell you?

(A) Only a small fraction of all molecules of this substance has enough kinetic energy to escape into the gas phase.

(B) The kinetic energy depends on the number of molecules.

(D) The energy needed to vaporize molecules is only a small fraction of all of the energy of the molecules based on the relative areas of the shaded and unshaded areas of this graph.

15 / 18

What is the most reasonable interpretation of the figure below?

(A) Based on the numbers on the axes, this is a plot of boiling points of some compounds.

(B) The figure shows that H₂O, NH₃, and HF have unusually high boiling points because the lines on the graph of similar compounds are not extended.

(D) The figure illustrates experimental error where the boiling point of CH4 must be an error.

16 / 18

In which of the following are the intermolecular forces listed from the strongest to the weakest for a single attraction?

(A) Dipole-dipole > London > hydrogen bonds

(B) Hydrogen bonds < dipole-dipole < London

(D) London > hydrogen bonds > dipole-dipole

17 / 18

In which of the following are the intermolecular forces listed from the strongest to the weakest for a single attraction?

(A) Dipole-dipole > London > hydrogen bonds

(B) Hydrogen bonds < dipole-dipole < London

(D) London > hydrogen bonds > dipole-dipole

18 / 18

Which of the following consistently have the highest melting points and why?

(A) Metals because the conducting electrons bind metal atoms very strongly using Coulomb forces

(B) Salts since they have very strong attractions between ions

(D) Molecules having resonance structures since they can shift forms instead of breaking

Your score is

Free-Response Questions

Answer the following questions concerning the properties of gases and the theories used to explain their behavior.

(a) Propane gas, C₃H₈, is used extensively as a fuel for gas grills. The complete combustion of this gas in the presence of oxygen produces carbon dioxide gas, water vapor, and heat.

(i) Write a balanced chemical equation for this combustion reaction.

(ii) Assuming the reaction is proceeding in the presence of excess oxygen, how many liters of carbon dioxide will be produced from a 5.0 L tank at 28 °C and a pressure of 745 mm Hg?

(iii) In some cases, not enough oxygen is present to yield a complete combustion of the gas. So carbon monoxide is produced. Write a balanced equation for the incomplete combustion of propane.

(b) A student performed the decomposition of potassium chlorate, KClO₃, to produce oxygen and potassium chloride. In order to collect the oxygen safely, the student used water displacement.

(i) Write the balanced chemical equation for this reaction.

(ii) How much oxygen gas (in mL) did the student collect if 0.25 g of KClO3 were heated at 25 °C and 735 mm Hg? (The vapor pressure of water at 25 °C is 23.8 mm Hg.)

(iii) The theoretical volume of oxygen gas calculated by the student for the gas was 76 mL. Is this number higher or lower than the answer for (ii)? Explain the error the student made in his/her calculation.