Fluorine (A) is not a transition metal, so its ionized counterparts will have a valence octet of electrons implying no unpaired electrons. (B), (C), (D) are all transition metals; however (B) and (C), commonly oxidize to the 2 and 3 positive states, respectively, which fill their d subshells. Iron (D) commonly oxidizes to the 2 positive state, which gives one extra s-subshell electron. This unpaired electron helps to give iron its magnetic properties and explains why iron in the body is further oxidized to the 3 positive state (to avoid inductive currents that could damage protein structure).
36. D
Following the Aufbau principle, the order of orbital filling should produce [Ar]4s23d4 as the electronic configuration for chromium. However, there is an overall increase in stability for the molecule if the d-subshell can be half-filled. Because of this, an electron will be moved from the 4s-subshell into the 3d-subshell giving (D) as the correct answer.
PASSAGE IV
37. A
Henry’s law states that the amount of gas dissolved in a liquid is directly proportional to the partial pressure of the gas in equilibrium with the liquid. Therefore, Henry’s law can be used to calculate the concentration of oxygen in water using the partial pressure of oxygen in air. Boyle’s law (B) deals with the relationship between the pressure and volume of gases, but does not address concentration of gases in water. Raoult’s law (C) pertains to the vapor pressure of a mixture of liquids, not a gas dissolved in a liquid. Le Châtelier’s principle (D) addresses changes to an equilibrium state and cannot stand alone to explain the equilibrium between a gas in air and in solution.
38. C
We can use the solubility constant for nitrogen provided in the passage, 8.42 × 10-7 M/torr, to solve this question. Because the units in the constant are in torr, we first convert 0.634 atm to torr by multiplying by 760 torr/1 atm. The partial pressure of nitrogen equals 481.8 torr. Multiplying the pressure by the constant 8.42 × 10-7 M/torr gives us 4.06 × 10-4 M nitrogen. The units for the answer are in g/L, so we multiply by the molar mass of nitrogen, 28 g/mole, to get our answer of 1.14 × 10-2 g/L.
39. B
The solubility constants provided in the passage can be used to determine that helium is the least soluble gas. A soluble gas is not desired because we want to minimize gas bubbles in the body. Moreover, helium is an inert gas, meaning it does not readily react with other gases. Whether helium is diatomic (A) has no bearing on its use in scuba tanks. Many gases are present in trace amounts in the water (D), so this fact alone could not account for the use of helium in scuba tanks.
40. B
This is a classic ideal gas law problem using
41. D
Immediate isolation in a hyperbaric chamber is the most effective and common treatment for those suffering from severe decompression sickness. The chamber recreates a high-pressure environment to allow gas bubbles to dissolve back into body fluids and tissues. The chamber can be brought back to normal pressure slowly in order to allow the body to adjust to the decreased pressure. Helium gas administration (A) or gas and air mixture (B) would not rid the body of excess gas bubbles. In fact, it might increase the gases bubbles and make symptoms worse. A hypobaric chamber (C) would certainly make symptoms worse because it decreases the pressure below 1 atm.
42. C
The solubility of gas in liquids decreases with an increase in liquid temperature. The warming of oceans has resulted in less dissolved oxygen and many oxygen-depleted “dead zones.” It is true that carbon dioxide has increased ocean acidity (A), but acidity alone cannot account for decreased oxygen levels. A predator shark may explain why certain fish are dying off (B), but it would not explain the decrease in oxygen. If rainfall did increase water levels in the ocean (D), the oxygen levels would equilibrate (as per Henry’s law) between the ocean and atmosphere to allow more dissolved oxygen in the oceans.
43. C
This is a
44. B
