Kaplan MCAT General Chemistry Review

A. [Ar]3d⁴5s²

B. [Kr]4d⁵5s¹

C. [Ar]4s¹4p⁵

D. [Ar]3d⁵4s¹

PASSAGE IV (QUESTIONS 37–45)

Decompression sickness involves symptoms that arise from exposure to a rapid decrease in ambient pressure. Decompression sickness can occur in multiple scenarios of decreased pressure and is most prevalent when divers return to the surface of water after a deep dive. If a diver ascends quickly and does not carry out decompression stops, gas bubbles can form in the body and create a multitude of adverse symptoms.

A diver experiences an increase in pressure when submerged many feet under water. Inert gases in the high-pressure environment dissolve into body tissues and liquids. When a diver comes back to the water’s surface and the pressure decreases, the excess gas dissolved in the body comes out of solution. Gas bubbles form if inert gas comes out of the body too quickly. These bubbles are unable to leave through the lungs and subsequently cause symptoms such as itching skin, rashes, joint pain, paralysis, and even death.

At sea level the pressure exerted on one square inch is equal to 14.7 pounds, or 1 atm. In water, an additional 1 atm of pressure is exerted for every 33 feet (about 10 m) below sea level. In addition to the decompression sickness, there are other conditions of which divers must be aware that arise from specific gases as a result of the high-pressure environment. For example, increased concentrations of nitrogen in the body lead to nitrogen narcosis. A diver with nitrogen narcosis feels intoxicated and experiences loss of decision-making skills due to nitrogen’s anesthetic quality. The table below provides a list of gases and their corresponding solubility constants in water at 298 K.

Gas k (M torr ^–1) CO₂4.48 × 10^–5O₂1.66 × 10^–6He5.1 × 10^–7H₂1.04 × 10^–6N₂8.42 × 10^–7

37. What theory could be used to determine the amount of oxygen that is dissolved in water at sea level?

A. Henry’s law

B. Boyle’s law

C. Raoult’s law

D. Le Châtelier’s principle

38. What is the solubility (g/L) of N₂ in water (25° C) when the N₂ partial pressure is 0.634 atm?

A. 3.19 × 10^-1 g/L

B. 1.5 × 10^-2 g/L

C. 1.14 × 10^-2 g/L

D. 1.5 × 10^-5 g/L

39. Helium is mixed with oxygen in the scuba tanks of divers in order to dilute the oxygen. Why is helium chosen over other gases for this purpose?

A. It is not a diatomic gas.

B. It is less soluble in aqueous solutions and so does not dissolve in body tissues and fluids.

C. It can react with other gases that may dissolve in the body to reverse gas bubble formation.

D. It is present only in trace amounts in water.

40. A scuba tank is filled with 0.32 kg O₂ that is compressed to a volume of 2.8 L. If the temperature of the tank equilibrates with the water at 13° Celsius, what is the pressure inside the tank?

A. 111 atm

B. 83.9 atm

C. 54.6 atm

D. 290 atm

41. Which of the following would you recommend for a diver suffering from decompression sickness?

A. Administration of helium gas

B. Administration of a gas and air mixture, which contains 50 percent nitrous oxide

C. Confinement in a hypobaric chamber

D. Confinement in a hyperbaric chamber

42. The underwater environment in the world’s oceans is rapidly changing. Recent years have seen drastic shifts in the ecosystem due to human activity and its impact on the environment. Many populations of fish that rely heavily upon oxygen are declining at extraordinary rates, whereas other ocean species that can survive in oceanic regions of oxygen-depletion are on the rise. What is the most likely explanation, based on scientific theory, for the decline in dissolved oxygen in the world’s oceans?

A. Carbon dioxide pollution has increased ocean acidity.

B. A new species of predator shark preys on fish in oxygen-rich regions.

C. The average temperature of the oceans is rapidly increasing.

D. Increased rainfall has added water to oceans without adding more oxygen.

43. A scuba tank contains 0.38 kg of oxygen gas under high pressure. What volume would the oxygen occupy at STP?

A. 0.27 L

B. 35 L

C. 266 L

D. 11 L

44. At 1 atm, the solubility of pure nitrogen in the blood at normal body temperature (37° C) is 6.2 × 10^-4 M. If a diver is at a depth where the pressure is equal to 3 atm and breathes air (78% N₂), calculate the concentration of nitrogen in the diver’s blood.

A. 1.3 × 10^-3 M

B. 1.4 × 10^-3 M

C. 1.5 × 10^-5 M

D. 1.9 × 10^-3 M

45. Consider two scuba tanks at sea level and 25° C. Tank 1 is filled with oxygen, and tank 2 is filled with a mixture of oxygen and helium. Will there be a difference in the root-mean-square velocities between these two tanks?

A. Yes, tank 2 has a higher root-mean-square velocity.

B. Yes, tank 1 has a higher root-mean-square velocity.

C. No, they will have the same root-mean-square velocity.

D. The root-mean-square velocity cannot be calculated for the tanks.

PASSAGE V (QUESTIONS 46–52)