Kaplan MCAT General Chemistry Review

3. A leak of helium gas through a small hole occurs at a rate of 3.22 × 10^-5 mol s^-1. Compare the leakage rates of neon and oxygen gases to helium at the same temperature and pressure.

A. Neon will leak faster than helium; oxygen will leak slower than helium.

B. Neon will leak faster than helium; oxygen will leak slower than helium.

C. Neon will leak slower than helium; oxygen will leak slower than helium.

D. Neon will leak slower than helium; oxygen will leak faster than helium.

4. A 0.040 gram piece of magnesium is placed in a beaker of hydrochloric acid. Hydrogen gas is generated according to the following equation:

Mg (s) + 2 HCl (aq) MgCl₂ (aq) + H₂ (g)

The gas is collected over water at 25°C, and the pressure during the experiment reads 784 mm Hg. The gas displaces a volume of 100 mL. The vapor pressure of water at 25°C is approximately 24.0 mm Hg. From this data, calculate how many moles of hydrogen are produced.

A. 4.22 × 10^-3 moles hydrogen

B. 4.09 × 10^-3 moles hydrogen

C. 3.11 moles hydrogen

D. 3.20 moles hydrogen

5. The properties of ideal gases state that ideal gases

I. have no volume.

II. have no attractive forces between them.

III. have no mass.

A. I, II, and III

B. I only

C. I and II only

D. I and III only

6. An 8.01 g sample of NH₄NO₃ (s) is placed into an evacuated 10.00 L flask and heated to 227°C. After the NH₄NO₃ totally decomposes, what is the approximate pressure in the flask?

NH₄NO₃ (s) N₂O (g) + H₂O (g)

A. 0.600 atm

B. 0.410 atm

C. 1.23 atm

D. 0.672 atm

7. The kinetic molecular theory states that

A. the average kinetic energy of a molecule of gas is directly proportional to the temperature of the gas in Kelvin.

B. collisions between gas molecules are inelastic.

C. elastic collisions result in a loss of energy.

D. all gas molecules have the same kinetic energy.

8. The plots of two gases at STP are shown below. One of the gases is 1.0 L of helium, and the other is 1.0 L of bromine. Which plot corresponds to each gas and why?

A. Curve A is helium and curve B is bromine, because helium has a smaller molar mass than bromine.

B. Curve A is helium and curve B is bromine, because the average kinetic energy of bromine is greater than the average kinetic energy of helium.

C. Curve A is bromine and curve B is helium, because helium has a smaller molar mass than bromine.

D. Curve A is bromine and curve B is helium, because the average kinetic energy of bromine is greater than the average kinetic energy of helium.

9. A balloon at standard temperature and pressure contains 0.20 moles of oxygen and 0.60 moles of nitrogen. What is the partial pressure of oxygen in the balloon?

A. 0.20 atm

B. 0.30 atm

C. 0.60 atm

D. 0.25 atm

10. The temperature at the center of the sun can be estimated based on the approximation that the gases at the center of the sun have an average molar mass equal to 2.00 g/mole. Approximate the temperature at the center of the sun using these additional values: The pressure equals 1.30 × 10⁹ atm, and the density at the center equals 1.20 g/cm³.

A. 2.6 × 10⁷ K

B. 2.6 × 10¹⁰ K

C. 2.6 × 10⁴ K

D. 2.6 × 10⁶ K

11. The gaseous state of matter is characterized by the following properties:

I. Gases are compressible.

II. Gases assume the volume of their container.

III. Gas particles exist as diatomic molecules.

A. I and II only

B. I and III only

C. III only

D. I, II, and III

12. A gas at a temperature of 27°C has a volume of 60.0 mL. What temperature change is needed to increase this gas to a volume of 90.0 mL?

A. A reduction of 150°C

B. An increase of 150°C

C. A reduction of 40.5°C

D. An increase of 40.5°C

13. A gaseous mixture contains nitrogen and helium and has a total pressure of 150 torr. The nitrogen particles comprise 80 percent of the gas, and the helium particles make up the other 20 percent of the gas. What is the pressure exerted by each individual gas?

A. 100 torr nitrogen, 50.0 torr helium

B. 120 torr nitrogen, 30.0 torr helium

C. 30.0 torr nitrogen, 150 torr helium

D. 50.0 torr nitrogen, 100 torr helium

14. In which of the following situations is it impossible to predict how the pressure will change for a gas sample?

A. The gas is cooled at a constant volume.

B. The gas is heated at a constant volume.

C. The gas is heated, and the volume is simultaneously increased.

D. The gas is cooled, and the volume is simultaneously increased.

Small Group Questions

1. How does the addition or removal of gas B from a vessel affect the partial pressure of gas A?

2. Is hydrogen bonding present in steam?

Explanations to Practice Questions

1. A