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Unit 3

3.15 MC Answers and Review

6 min read•december 29, 2022

AP Chemistry 🧪

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Answers and Review for Multiple Choice Practice on Intermolecular Forces and Properties

⛔STOP ! ⛔ Before you look at the answers, make sure you gave this practice quiz a try so you can assess your understanding of the concepts covered in Unit 3. Click here for the practice questions: AP Chemistry Unit 3 Multiple Choice Questions

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Facts about the test: The AP Chemistry exam has 60 multiple choice questions and you will be given 1 hour 30 minutes to complete the section. That means it should take you around 15 minutes to complete 10 questions. *The following questions were not written by College Board and although they cover information outlined in the AP Chemistry Course and Exam Description the formatting on the exam may be different.

1. Which of the following temperature and pressure conditions is a real gas considered to be most ideal?

A. 500 K and 0.1 atm

B. 200 K and 0.1 atm

C. 500 K and 1 atm

D. 200 K and 1 atm

Explanation: A gas is considered to be most ideal at high temperatures and low pressures. The correct option had the highest temperature and lowest pressure.

Study the ideal gas law in this guide!

2. What is the temperature (in Celsius) of a 0.250 mol of a gas that occupies 75.0 L at 0.155 atm of pressure?

A. 566°C

B. 5.59°C

C. 293°C

D. You need to know the identity of the gas in order to determine the temperature.

Explanation: Using the ideal gas law (PV=nRT), one can determine temperature of a gas given pressure, volume, and number of moles. Don't forget to convert to Celsius by subtracting 273 from the temperature value.

Study the ideal gas law in this guide!

3. Which of the following substances has the highest melting point?

A. Water (H_2O)

B. Methane (CH_4)

C. Chlorine Gas (Cl_2)

D. Magnesium Oxide (MgO)

Explanation: Magnesium oxide is an ionic compound. Ionic compounds have high melting points compared to their covalent counterparts.

Watch this video on properties of solids!

4. Which of the following statements correctly identifies why carbon tetrabromide (CBr_4) has a larger boiling point than bromomethane (CH_3Br)?

A. Bromomethane is polar and has dipole-dipole forces, whereas carbon tetrabromide is nonpolar and has london dispersion forces.

B. Carbon tetrabromide is ionic while bromomethane is covalent.

C. Carbon tetrabromide is more polarizable than bromomethane, because it has more electrons.

D. Carbon tetrabromide is an unsymmetrical molecule while bromomethane is symmetrical making it nonpolar.

Explanation: While carbon tetrabromide is a nonpolar molecule, it is significantly larger than bromomethane. When molecules are large, they contain more electrons. With more electrons, these molecules have stronger London dispersion forces.

Read this guide on intermolecular forces!

5. Which molecule has the highest viscosity?

A. Methanol (CH_3OH)

B. Chloromethane (CH_3Cl)

C. Liquid bromine (Br_2)

D. Nitrogen trichloride (NCl_3)

Explanation: Methanol has hydrogen bonds, which is the strongest intermolecular force. Chloromethane and nitrogen chloride have dipole-dipole forces, while liquid bromine contains London dispersion forces. The stronger the intermolecular force, the higher the viscosity.

Read this guide on intermolecular forces!

6. Which of the following substances is a network covalent solid?

A. Dry Ice (CO_2)

B. Diamond (Carbon)

C. Brass (Cu & Zn)

D. Sodium Fluoride (NaF)

Explanation: Diamonds are network covalent solids which are essentially giant molecules with covalent bonds between the carbon atoms. Dry ice is a molecular solid, brass is a metallic solid, and sodium fluoride is an ionic solid.

Watch this video on properties of solids!

7. What is the mass of sodium chloride (M = 58.44 g/mol) required to make 25 mL of a 3.5 M solution?

A. 5.11 g

B. 5110 g

C. 87.5 g

D. 87,500 g

Explanation: Molarity is equal to the moles of the solvent divided by the liters of the solution. Once the moles of the sodium chloride is determined, multiply by its molar mass.

Watch this video on solutions and mixtures!

8. Which of the following substances is most soluble in water?

A. Carbon tetrafluoride (CF_4)

B. Sulfur dichloride (SCl_2)

C. Liquid Bromine (Br_2)

D. Ethanol (CH_3CH_2OH)

Explanation: Ethanol is the most soluble in water since it's the only option with hydrogen bonds. "Like dissolves like," meaning that molecules with similar IMFs will be soluble.

Read this guide on solubility!

9. Which type of radiation is associated with electrons transitioning between energy levels?

A. Infrared radiation

B. UV radiation

C. Microwave radiation

D. Radio Radiation

Explanation: UV radiation is associated with electronic transitions. Infrared radiation is associated with molecular vibrations. Microwave radiation is associated with molecular rotations.

Read this guide on the photoelectric effect!

10. A 0.55 M solution of HCl has a volume of 125mL. What amount of distilled water is added to dilute the solution to 0.35 M?

A. 80. mL

B. 196 mL

C. 45 mL

D. 71 mL

Explanation: First, use the dilution equation (M_1V_1 = M_2V_2) in order to determine the new volume of the diluted solution. Then subtract the old volume from the new volume to determine the amount of water added.

Watch this video on solutions and mixtures!

11. What is the identity of a diatomic gas molecule that has a density of 2.89 g/L at 1.00 atm and 25°C?

A. Hydrogen Gas (M = 2.02 g/mol)

B. Chlorine Gas (M = 70.90 g/mol)

C. Fluorine Gas (M = 38.00 g/mol)

D. Nitrogen Gas (M = 28.02 g/mol)

Explanation: In order to determine identity, one must use the following deviation of the ideal gas law, PM = dRT. After plugging in all known values, we determine that the molar mass of the unknown diatomic is chlorine gas.

Study the ideal gas law in this guide!

12. What is the danger of heating a rigid container of helium gas?

A. The pressure of the container will increase as the temperature increases. This could cause the container to explode.

B. Heating helium gas causes it to decompose into a poisonous gas that is dangerous to inhale.

C. Heating the container will cause the average kinetic energy of the helium particles to decrease.

D. There is no danger in heating a rigid container of helium gas.

Explanation: Pressure and temperature are directly related at constant volume. This means that at higher temperatures, pressures increase. With a larger pressure, the container could explode.

Read this guide on Kinetic Molecular Theory!

13. What is the concentration of chloride ions [Cl^-] in a 1.0 L solution that contains 55 g of magnesium chloride (MgCl_2, M = 95.21 g/mol)?

A. 0.577 M

B. 1.16 M

C. 3.46 M

D. 1.73 M

Explanation: Molarity is equal to the moles of the solute divided by the liters of the solution. When magnesium chloride dissociates into water it produces twice as many chloride ions.

Watch this video on solutions and mixtures!

14. What is the wavelength of a photon that has an energy of 1.55x10^-19 J?

A. 1.28x10^-6 m

B. 2.34x10^14 m

C. 4.65x10^-11 m

D. 3.08x10^24 m

Explanation: The wavelength of a photon is directly proportional to the frequency of the photon (c=λν). Frequency and energy are directly related (E=hν).

Read this guide on absorption!

15. Copper sulfate creates an extraordinarily blue solution in water. Which of the following experimental techniques could a scientist use to determine the concentration of copper sulfate based on absorbance?

A. Gravimetric analysis

B. Titration

C. Mass Spectroscopy

D. Photospectroscopy

Explanation: Photospectroscopy relates the concentration of a solution to the amount of light that passes through it. This is called Beer-Lambert's Law (A=εbc). While Gravimetric analysis and titration may be used to determine concentration, they do not do so using absorption.

Read this guide on Beer-Lambert's Law!

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