Princeton Review MCAT Exam 1: ChemPhys Actual Full Questions And Answers Well Elaborated.

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? - correct 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? - correct 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: - correct 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 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? - correct 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graph shows how the charge decreased as the capacitor discharges, which occurs when the voltage between the plates is no longer maintained.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+ pump (the voltage source) stopped working, the voltage between the sides of the membrane would no longer be maintained. A Q-switched laser can be used to treat skin blemishes and to remove tattoos. The Q switch momentarily interrupts the inducing light creating a build-up of energy within the crystal. This does not increase the overall energy of the laser, but concentrates it into shorter time periods or pulses. A longer interruption with the Q-switch most likely would increase the: - correct answer B. Power of each laser pulse -Since the overall energy of the laser does not change, neither will the frequency, wavelength, nor work done by the laser. - Concentrating the energy into a shorter time period increases the power of each pulse The passage describes the simplest interpretation of the basic properties of a laser, but some modifications are necessary to build a workable laser. Which of the following, if true, are possible problems with the simple model described in the passage? I: It is difficult to keep a collection of atoms in their excited state long enough to be stimulated to emit the induced photon II: Atomic energy levels are quantized III: Atoms in the crystal that happen to be in their ground state will undergo absorption, thereby removing photons from the beam as it builds up. - correct answer C. I and III only - The laser acquires its intense energy by induced emission, so if statement I were true, then too many atoms would emit energy by spontaneous emission, decreasing the efficacy of the laser - If statement III is true this would also represent a mechanism by which the laser's intensity would be reduced. 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: - correct 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) - correct 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+ - correct 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. If a fully saturated solution of AgI, with precipitate present, were treated with NaCl instead of NaI, which of the following observations is likely? - correct answer D. The concentration of (I-) increases -Unlike NaI, NaCl does not have a common ion with AgI and will therefore NOT cause a decrease in the solubility for AgI with increasing concentration. - As the dissolved (NaCl) concentration increased, AgCl will be precipitated from solution, which will enable additional AgI to dissolve. This increased dissolution of AgI will cause the increase in (I-), even as (Ag+) levels remain low. Raclopride-H+ can best be described as: - correct answer A. an amphiphilic molecule that has two stereoisomers - Lewis bases are electron pair donors, and as H+ has no electrons these options can be eliminated. -Raclopride-H+ has a hydrophobic halogenated aromatic portion, and a hydrophilic side chain (protonated amine), making it an amphipathic molecule. -The number of stereoisomers a compound may have is given by the formula 2n, where n is the number of chiral centers present. It has one chiral center, so there are 2 stereoisomers. In the second step of the reaction shown in Figure 1, the role of water can best be described as a(n): - correct answer B. Nucleophile -Protonation of the carbonyl group at the oxygen atom is the fist step of the reaction in Figure 1 makes the carbonyl-carbon a good electrophile. Water acts as the nucleophile, attacking the electrophilic carbonyl at the carbon atom shown bellow. Which of the following occur(s) in the reaction shown in Figure 1? I: Oxidation II: Elimination III: Saponification - correct answer B. II only - Item II is true. During the reaction, an ester is converted into a carboxylic acid. Carboxylic acid derivatives undergo an addition reaction followed by an elimination reaction. Which of the following can the researches conclude strictly from the data shown in Figure 2? - correct answer C. Lipid hydrolysis with raclopride is significantly faster than any background degradation process. -Figure 2 does show that the rate of background lipid hydrolysis is comparatively much slower than raclopride-mediated lipid hydrolysis A converging glass lens forms a real image of a red object at a distance equal to twice its focal length. If a blue object is placed adjacent to the red object, will its image form closer to the lens or father from the lens than the image of the red object? - correct answer B. Closer, because blue light is refracted more due to its shorter wavelength -The refractive index of a transparent medium increases with increasing frequency of the transmitted light. Thus, the refractive index of the lens for blue light would be slightly higher than for red light. This would imply that blue light experiences more refraction than red light. Since the lens is a converging one, the blue light would be bent more sharply toward the axis than the red light, so the image of the blue object would be formed closer to the lens. As an ideal fluid flowing in a narrow pipe passes from a region of cross-sectional diameter d to a region of cross-sectional diameter d/2, the flow speed of the fluid will: - correct answer D. Increase by a factor or 4 -If the diameter of the flow tube decreases by a factor of 2, the cross-sectional area decreases by a factor of 2^2=4. Since the continuity equation implies that flow speed is inversely proportional to the cross-sectional are of the flow tube, the flow speed will increase by a factor of 4. What is a meso compound? - correct answer An epoxide that has two chiral centers, and has a plane of symmetry. Which one of the following statements concerning the SN2 reaction mechanism is true? - correct answer C.It proceeds best with primary substrates and is a one-step reaction - SN2 cannot operate with a tertiary substrate because the nucleophile must attack at the same time the leaving group leaves, and tertiary substrates are too statically hindered. C is the best answer because unhindered substrates allow the nucleophile to attack while the leaving group leaves. What change in cytosolic conditions would most directly disrupt the catalytic function of the CTA1, Glu23, and Glu57 residues? - correct answer B. Decreased pH - Figure 1 indicates that the CTA1 domain acts on G-proteins found on the cytoplasmic phase of membranes, and that the side-chain carboxylic acid groups of Glu23 and Glu57 function catalytically in ADP-ribosylation in their conjugate base form. Decreasing cytosolic pH would increase the likelihood of protonating and inactivating either residue, thus directly disrupting enzyme function. The results of the experiment suggests that - correct answer A. The ability of ArfGAP1 to interact with (delta17) Arf1 depends on an alpha-helical structure - the kinetic parameters of wild type Arf1 without ArfGAP1 and of (delta17) Arf1 are nearly identical. Combined with the passage information that the structure of (delta 17) Arf1 differs from that of wild type Arf1 at the GTP binding site, and that ArfGAP1 stabilized the Arf1 GTP binding site, the most likely conclusion is that (delta17) Arf1 is unable to interact with ArfGAP1 at the binding site because of the structural disruption of the alpha helix at the GTP binding site. A cyclist collides with a tree, and the collision creates an intense compressive stress on the cyclist's left humerus (upper arm bone), causing a fracture. Which of the following changes in the initial conditions most likely could have prevented the fracture? - correct answer A. A decrease in his velocity by a factor of two -The cyclist's kinetic energy just before the impact will be converted into elastic and inelastic energy of deformation upon impact (related to the area under the stress versus strain curve) to cause damage to the tree and to the cyclist. Decreasing this kinetic energy will result in a less violent collision. Because velocity is squared in the kinetic energy, a decreased in the cyclist's velocity would have the greatest effect in lowering his KE. If the graph in Figure 1 were redrawn for cartilage undergoing tensile stress, then the angle would be: - correct answer C. Smaller, because cartilage has a smaller Young's modulus than does bone