Princeton Review MCAT Exam 1:
ChemPhys with Complete
Solutions
A mixture of aspartate and phenylalanine is separated into its component molecules
by thin layer chromatography on a silica plate eluted with benzene.
Which of the following best explains why this separation occurs? - ANSWER - D.
Phenylalanine will move father with the mobile phase, because it has a non polar
side chain
-the side chain of aspartate is CH2COO- which is very POLAR while the side chain of
phenylalanine CH2Ph is NONPOLAR. Because the mobile phase is NONPOLAR the
molecule that is less polar will move farther in the mobile phase
According to the figures, decreasing which of the following would create the
greatest increase in charge stored per unit voltage on an axon membrane in its rest
state? - ANSWER - D. Thickness of the membrane
-change stored per unit voltage Q/V is the definition of capacitance, C. The equation
for the capacitance of the parallel-plate capacitor is C=keoA/d
k: dielectric constant
eo: universal constant
A: the area of each plate
d: the distance between the plates
Decreasing the thickness of the membrane (decreasing d) would increase the
capacitance
Ouabain irreversibly inhibits the Na+/K+ pump. The effect of this on the equivalent
circuit model for the resting axon would be to cause: - ANSWER - D. decreased
potential difference across the resistors and the capacitor
, -The resistors and the capacitors are in parallel, so they must have the same
potential difference. If the source of the potential difference (the Na+/K+ pump) is
prevented from operating, then the common potential difference across the
resistors and the capacitor would decrease
A CO2 laser used as a laser scalpel produces a beam of laser light with a
wavelength of 10.6 micrometers. Compared to the excited electrons in the laser
shown in Figure 1 (1.06 micrometers) the excited electrons in the CO2 laser most
likely have: - ANSWER - D. A smaller energy difference between their normal state
and their excited state.
-The wavelength of the CO2 laser is 10 times GREATER than the wavelength of the
laser shown in figure 1. Therefore the frequency and the energy of the CO2 laser are
10 times LOWER.
Which one of the following is true of Reaction 1?
AgI (s) (back and forth arrows) Ag+(aq) + I- (aq) - ANSWER - C. The oxidation state
of Ag does not change
-Reaction 1 is NOT a redox reaction. The oxidation states of Ag and I in AgI(s) are +1
and -1 respectively, and neither changes during dissolving.
How many grams of NaI should be added to 500 mL of a saturated solution of AgI to
make a solution that is 1.5 x 10-15 M Ag+ - ANSWER - B. 4.5 g
-Figure 1 indicates that when (AgI)= 1.5 x10-15 M, the concentration of NaI=0.06M.
In 500 mL (0.5 L), this solution should contain 0.030 mol NaI. Since the molar mass
of NaI is 150 g/mol, this amounts to 4.5 g of NaI.
The change in Q the magnitude of charge on each surface of the axon membrane
that is depicted in the graph above, could be produced by which of the following? -
ANSWER - C. Inactivity of the Na+/K+ pump
-The graph shows how the charge decreased as the capacitor discharges, which
occurs when the voltage between the plates is no longer maintained. If the Na+/K+
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