AAMC MCAT Practice Exam 1 with correct answers 2023

AAMC MCAT Practice Exam 1 with correct answers 2023 In the chromatography of the reaction mixture, water absorbed on cellulose functioned as the stationary phase. What was the principal factor determining the migration of individual components in the sample? A) Hydrogen bonding B) Solute concentration C) Stationary phase concentration D) Thickness of paper - correct answer A) Hydrogen bonding The answer to this question is A because the relative amount of hydrogen bonding to the stationary phase will determine the relative rate of migration of the various components in the sample. What assumption is being made if scientists conclude that aspartic acid was formed by the prebiological synthesis in the passage? A) Aspartic acid is unstable at temperatures below 150 degrees C. B) All of the malic acid underwent the dehydration reaction to form fumaric/maleic acid. C) Compound A and cyanide were available on primitive Earth. D) The reaction between ammonia and fumaric acid was catalyzed by the presence of water. - correct answer C) Compound A and cyanide were available on primitive Earth. he answer to this question is C since, in order for the experimental reaction sequence to be relevant to the primordial formation of aspartic acid, the starting materials used (Compound A and cyanide) are assumed to have been available. According to the developed chromatography plate shown below, what is the approximate Rf value of aspartic acid? aspartic acid = 2 solvent front = 10 A) 0.20 B) 0.50 C) 5 D) 10 - correct answer The answer to this question is A (0.20) because Rf is the ratio of the distance travelled by the analyte relative to the solvent front during a chromatographic separation. Aspartic acid travelled two units, while the solvent front travelled ten units, giving an Rf of 2/10 = 0.20 for aspartic acid. Which of the following statements does NOT correctly describe the dehydration of malic acid to fumaric acid and maleic acid? A) The reaction occurs most readily with tertiary alcohols. B) The reaction involves the loss of a water molecule. C) The reaction has a carbocation intermediate. D) The reaction is stereospecific. - correct answer D) The reaction is stereospecific. The answer to this question is D because the fact that both fumaric and maleic acid are produced means that the dehydration of malic acid is NOT stereospecific. What type of functional group is formed when aspartic acid reacts with another amino acid to form a peptide bond? A) An amine group B) An aldehyde group C) An amide group D) A carboxyl group - correct answer C) An amide group The answer to this question is C because the functional group that forms during peptide bond formation is known as an amide group. If 2-pentanol replaces 1-pentanol in the reaction shown in Figure 3 (SN2), the rate of substitution is less because: A) the C-O bond in 2-pentanol is stronger than the C-O bond in 1-pentanol. B) there is a competing elimination reaction that slows the rate of substitution. C) there is more steric hindrance at the oxygen atom in 2-pentanol than in 1-pentanol, making protonation less likely. D) there is more steric hindrance at the 2-position of 2-pentanol than at the 1-position of 1-pentanol. - correct answer D) there is more steric hindrance at the 2-position of 2-pentanol than at the 1-position of 1-pentanol. The answer to this question is D because the rate of substitution of protonated alcohols is subject to steric hindrance. This inhibits the ability of nucleophiles to collide with the reacting electrophilic center and slows the rate of reaction. If a solution containing the compounds shown in Figure 4, is injected into a gas-liquid chromatograph, the first peak observed in the gc trace is attributable to which compound? A) Methyl-2-butanol B) Methyl-2-butene C) Chloro-2-methylbutane D) Bromo-2-mehtylbutane - correct answer B) Methyl-2-butene The answer to this question is B because 2-methyl-2-butene will exhibit the lowest molecular weight and also the weakest intermolecular forces of attraction. This substance will therefore migrate the fastest and be the first peak in the gas chromatograph (gc) trace. R vs. S stereochemistry* - correct answer R = clockwise C = counter-clockwise Acetic acid and ethanol react to form an ester product as shown below. In determining which reactant loses the -OH group, which of the following isotopic substitutions would be most useful? A) Replace the acidic H of acetic acid with D B) Replace the alcoholic H of ethanol with D. C) Replace the carbonyl oxygen of acetic acid with O-18. D) Replace the hydroxyl oxygen of ethanol with O-18. - correct answer D) Replace the hydroxyl oxygen of ethanol with O-18. The answer to this question is D because this experiment involves labeling a group which does not exchange with other groups present prior to reaction and will therefore give information about the true identity of the groups, which are exchanged during the reaction. A person whose eye has a lens-to-retina distance of 2.0 cm, can only clearly see objects that are closer than 1.0 m away. What is the strength S of the person's eye lens? (Note: Use the thin lens formula 1/O + 1/I = S) A) -50 D B) -10 D C) 51 D D) 55 D - correct answer C) 51 D The answer to this question is C because the strength of the eye lens is equal to the inverse of the focal length of the eye lens. Its numerical value is given by (1 m)-1+(0.02 m)-1=1 D+50 D=51 D. Which statement correctly describes how enzymes affect chemical reactions? Stabilization of: A) the substrate changes the free energy of the reaction. B) the transition state changes the free energy of the reaction. C) the substrate changes the activation energy of the reaction. D) the transition state changes the activation energy of the reaction. - correct answer D) the transition state changes the activation energy of the reaction. The answer is D because the stabilization of the transition state, not the substrate, provides binding energy that is used to lower the activation energy. Which of the following will decrease the percentage ionization of 1.0 M acetic acid, CH3CO2H(aq)?* A) Chlorinating the CH3 group B) Diluting the solution C) Adding concentrated HCl (aq) D) Adding a drop of basic indicator - correct answer C) Adding concentrated HCl (aq) The answer to this question is C because HCl is a strong acid that will increase the amount of H+ in solution and thus decrease the percentage of CH3CO2H that ionizes. When the current in the micro-robot's circuit increases and the resistance of the circuit remains constant, the voltage of the circuit: A) decreases B) increases C) is constant D) is zero - correct answer B) increases V = IR The answer to this question is B because according to Ohm's law, current is equal to voltage divided by resistance. If current increases and resistance is constant, then voltage increases as well. Knowing that the speed of light in the vitreous humor is 2.1 × 108 m/s, what is the index of refraction of the vitreous humor? (Note: The speed of light in a vacuum is 3.0 × 108 m/s.) A) 0.7 B) 1.4 C) 2.1 D) 3.0 - correct answer B) 1.4