MCAT Biological Science Practice Test Answers
1:B. Jones oxidations are carried out by the treatment of an alcohol or an aldehyde with a solution of CrO3 in mild sulfuric acid solution. A solution of K2Cr2O7 in concentrated sulfuric acid produces ‘chromic acid’, a very strongly oxidizing solution sometimes used as a ‘˜last resort’ to clean chemical residues from laboratory glassware. Chromic acid oxidizes organic compounds completely to CO2 and H2O, and does not stop at the carboxylic acid stage of the process. Potassium permanganate, KMnO4, and manganese dioxide, MnO2, are also used as oxidizing agents, but neither of these is the Jones’ reagent.
2:C. It is entirely possible that the molecules of the compound can decompose at the elevated temperatures before the boiling point of the material is attained. Reducing the pressure lowers the temperature at which materials boil, so distillation can occur before the material ever becomes hot enough to decompose.
High-boiling materials do boil at normal pressure, but at temperatures that are high enough to be a concern in regard to safety, energy use, etc.
Boiling point and vapor pressure are inversely related; higher vapor pressure means lower boiling point.
The melting point of a compound is not related to its boiling point.
3:C. Monosaccharides are simple sugar molecules, or single carbohydrate molecules, such as glucose and fructose.
They are cyclic compounds but do not have a carbonyl group when they are in that form, so they cannot be classified as either ketones or aldehydes.
They have several -OH groups, as carbohydrates do, but they are not carboxylic acids.
4:A. The electron-withdrawing power of the carbonyl O atom draws electron density through the C=O Ï’ bond away from the Î± C-H bonds. This makes it easier for the sp3 Î± carbon atom to hybridize to sp2 + p and form an extended Ï’ system. This renders the Î± position sufficiently acidic that a proton can be extracted by a strong base. The extra electron of the negative charge in the free p orbital is stabilized by delocalization into the carbonyl Ï’ orbital system. The negatively-charged ion formed by the extraction of an Î± proton is called an enolate ion because its structure is similar to the enol form of a carbonyl compound.
Tertiary amines are generally not sufficiently strong bases to extract an Î± proton.
5:C. Friedel-Crafts reactions use strong Lewis acids to activate the benzene ring to the replacement of H atoms by alkyl or aryl substituent groups. The Lewis acid catalyst coordinates the Ï’ system of the benzene ring and the halide of the alkyl or aryl halide. This produces a good electrophile that can add to the benzene ring and displace a proton. The reaction can also be used for halogenation and acylation of benzene ring structures.
Claisen condensation involves the addition of an enolate ion to an ester with loss of H2O from the initial product to form an enone structure.
Wittig reactions add a phosphine to a carbonyl group.
Bicycloannulation reactions add two new ring structures to a substrate molecule in one step.
MCAT Physical Science Practice Test Answers
1:A. In a closed system (when you ignore outside interactions), the total momentum is constant and conserved. The total energy would also be conserved, although not the sum of the potential and kinetic energy. Some of the energy from the collision would be turned into thermal energy (heat) for example. Nor is the total velocity conserved, even though the velocity is a component of the momentum, since the momentum also depends on the mass of the cars. The impulse is a force over time that causes the momentum of a body to change. It doesn’t make sense to think of impulse as conserved, since it’s not necessarily constant throughout a collision.
2:D. Since this is a head-on elastic collision, you could use conservation of kinetic energy and momentum to actually solve this problem. However, in this case, you only need to think through the answers to arrive at a correct conclusion. Clearly the ball after it’s struck won’t be going 0 m/s. And since this is an elastic collision, and it is hit by a much larger ball, it must be going faster than the larger ball was originally moving. Therefore, the ball will be moving at more than 10 m/s. If this were an inelastic collision where the balls stuck together, the ball would final velocity would be less than 10 m/s.
3:C. To determine how much work is done by a gravitational force, you should calculate the change in that object’s potential energy = mgh, where m = mass, g = the gravitational acceleration 9.8 m/s2 and h = height. Therefore, the work done only depends on the change in height and not on the path taken. In Answer A, the work done by gravity doesn’t have anything to do with friction, so this is not a good explanation. Friction is a separate force. Answer D, although true, doesn’t explain why the work doesn’t depend on the path.
4:B. Kinetic energy is the energy of motion and is defined as ½mv2. Using this equation, if you double the mass and the velocity of an object, you find KE = ½(2m‘)(2v‘)2 or 8 times the original KE. Therefore, the motorcycle has 8 times as much kinetic energy as the bicycle.
5:C. From the question, doubling distance would lower the gravitational force by a factor of 1/4, since the force is proportional to 1/R2. The gravitational potential would be 1/2 of the original because it is proportional to 1/R. Therefore, the ratio of the new force to the new potential would be 1/4 x 1/2, or 1/2 of the original ratio.
MCAT Verbal Reasoning Practice Test Answers
1:C. The placement of the blank indicates that the correct word will describe Sharon’s disposition, or temperament. Since her disposition draws friends to her, we know we are looking for a positive attribute. Aloof, patrician, and supercilious all suggest negative traits that would repel friends. The only logical choice is C, genial, which means ‘friendly and cheerful.’
2:D. What kind of statement would make a candidate into a laughingstock? You can eliminate pithy (meaning ‘to the point’), insightful (meaning ‘showing clear understanding’), and factual (meaning ‘containing facts’). Fatuous (meaning ‘silly, inane, foolish’) is obviously the correct choice.
3:A. The clue words lazy, rest, and hammocks all point to indolent, a synonym for lazy, as the correct choice here.
4:C. Knowing that ameliorate means ‘to improve, to make or become better’ will point you immediately to choice C as the correct answer. Abeyance (meaning ‘a state of temporary suspension’) does not fit the definition of Emerson’s idea, nor do vindication (meaning ‘justification’) or anticipation (meaning ‘the act of looking forward’).
5:B. The clue that Robert had many sleepless nights leads us to believe that he was worried. We know that he would not be worried about a congruity (meaning ‘harmony’ or ‘agreement’) between the house’s value and the amount owed. However, a disparity (meaning ‘difference’) might indeed cause worry. The other two choices do not make sense in the sentence, so they can be eliminated.