MCAT Question of the Day

How many liters of 0.3M HCl can be made from a 2L stock solution of 1.5M HCl? A. 10L B. 12L C. 6L D. 20L

Correct Answer: A. 10L M1V1 = M2V2 (0.3)(V1) = (1.5)(2) V1 = 10 L

If the hormone aldosterone is released in the bloodstream, which of the following is most likely to occur? A. Bile and lipid production will increase. B. The amount of glucose in the blood will decrease. C. The amount of calcium ions in the blood will decrease. D. The amount of salt reabsorbed in the kidneys will increase.

Aldosterone is a hormone released from the adrenal gland. Its presence in the blood helps the kidney's retain more sodium chloride (NaCl) in the nephrons, thereby desalinating the urine. Glucose regulation is controlled by the pancreas' release of insulin. Calcium ion levels are controlled by calcitonin and parathyroid hormone. The amount of water retained by the kidneys is controlled by the release of the antidiuretic hormone (ADH) or vasopressin. Aldosterone helps to retain water too, so the amount of water excreted by the body will decrease. Therefore, the correct answer is [D].

A laboratory shines a single beam of light into a fluid at an angle of 30°. Assuming the refractive index of air is 1, and the beam of light refracts at an angle of 60°, what is the refractive index of the unknown fluid? A. √3 B. 1/√3 C. 1/2 D. 2√3

Answer choice (B) is correct. In order to answer this question, we must use Snell's law, n1sin(θ1) = n2sin(θ2). Rearranging this equation, we find that n2 = 1 · sin(30)/sin(60) = (1/2)/(√3)/2) = 1/√3.

An object undergoing simple harmonic motion is observed to have a time interval of 4 seconds between the two extremes of its displacement from equilibrium. What is the frequency of this motion? A. 0.125 cycles/second B. 0.25 cycles/second C. 1.25 cycles/second D. 4 cycles/second

Correct Answer: A. 0.125 cycles/second Since it takes 4 seconds for the object to travel from one end of its displacement to the other (half a cycle), the time for a full cycle is 2(4 sec) = 8 sec. Thus frequency = 1/T = 1/8 = 0.125 Hz.

An electron moving parallel to a uniform magnetic field of 5 Tesla covers a distance of 25 cm. Calculate the force exerted on the electron by the magnetic field. 0 J 125 J 12.5 J 1.25 J

Correct Answer: A Recall that the equation for the force experienced by a moving charge in an electric field is F = qvBsinθ. Since sin(0) = 0, there is no force acting on the charge. The correct answer is (A). In order for a particle to experience a force due to a magnetic field, it must be charged, moving, and moving in a direction that is not parallel or antiparallel to the field. Even if the charge was moving in such a direction, we would need to know the velocity of the charge in order to determine the force.

A force of 1 minion can cause 1 gram to accelerate at 1 cm/s2. How many newtons are equivalent to 1 minion? A. 10-5 B. 10-1 C. 101 D. 105

Correct Answer: A. 10-5 1 newton = 1 kg*m/s2 Therefore: 1 (g*cm)/s2 = x (kg*m)/s2 -> 1(10-3kg)(10-2m) = 10-5

A hollow rubber ball, whose volume is 3 x 10-3m3 and has a mass of 1.0 kg) is held by a 1-meter-long string attached to the bottom of a large container of water. What is the tension in the string? A. 20 N B. 35 N C. 40 N D. 45 N

Correct Answer: A. 20 N There are two forces acting on the string. The buoyant force of the ball upward, the tension in the string downward, and the mass of the ball. Since the ball is stationary, these forces must cancel. Thus, T + w = B, which implies: T = B - w = pVg - mg = (103)(3 x 10-3)(10) - (1.0)(10) = 20 N

Which of the following occurs when the heart is in systole? A. Blood is pumped from the ventricles to the arteries. B. Blood is pumped from the veins to the heart. C. Blood is collected in both veins and arteries. D. Blood is collected in the right atria and right ventricle.

Correct Answer: A. Blood is pumped from the ventricles to the arteries. Systole is the state of contraction of the heart muscles. The heart contracts to pump blood out of the ventricles and into the arteries to move the blood to the body. During diastole or when the heart is resting, blood collects in the chambers of the heart. Arteries carry blood away from the heart and veins carry blood back to the heart. During systole, the blood is being pumped away from the heart, thereby the use of arteries is essential. The only answer option that aligns with the correct function of the heart during systole is [A].

According to scientists, Oparin and Haldane, which of the following gases were present in the primitive atmosphere? A. CH4, NH3, H2, H2O B. CO2, NH3, H2, H2O C. N2, O2, H2, H2O D. CH4, NH3, O2, H2O

Correct Answer: A. CH4, NH3, H2, H2O In the primitive atmosphere, no O2 was present as most organisms used chemosynthesis to create organic compounds. The Oparin and Haldane hypothesis states that methane (CH4), ammonia (NH3), hydrogen (H2), and water (H2O) were the only gases present. It was after the Miller and Urey experiment that it was proven that these gases and lightning could have given rise to simple organic compounds that then later evolved into more complex forms of life.

The lethal poison cyanide causes death by interfering with cellular respiration. What is cyanide's mechanism of toxicity? A. Cyanide blocks the passage of electrons from cytochrome oxidase a3 to oxygen B. Cyanide inhibits the binding of ATP to ATP synthase C. Cyanide covalently binds to coenzyme Q (ubiquinone) D. Cyanide breaks down the proton gradient across the inner mitochondrial membrane

Correct Answer: A. Cyanide blocks the passage of electrons from cytochrome oxidase a3 to oxygen Cyanide blocks the passage of electrons from cytochrome oxidase a3 to oxygen since it has a very high binding affinity for the enzyme. The cell cannot use oxygen so even if the person can breathe, the cells cannot use the oxygen that is delivered to tissues. Oligomycin inhibits the electron transport chain by directly affecting ATP synthase. A class of poisons called uncouplers makes the lipid bilayer permeable to hydrogen ions, which eliminates the electrochemical gradient.

Which of the following statements regarding electric current is true? A. Electric current will only flow from a higher potential to a lower potential. B. Electric current will only flow from a lower potential to a higher potential. C. Oscillate between potentials of higher and lower energy. D. Remain in equilibrium

Correct Answer: A. Electric current will only flow from a high potential to a lower potential. Electric current moves in the direction positive charges move in. Therefore, the electric flow of current flows from the point of higher potential to lower potential, similar to how water falls from the top of the waterfall to the bottom.

Once a mammalian zygote has become a blastocyst and implants itself into the uterine wall, it will develop into? A. Gastrula B. Embyroblast C. Trophoblast D. Oocyte

Correct Answer: A. Gastrula The correct answer is A. The oocyte and morula are both precursors to the blastula stage. The embryoblast and the trophoblast are both components of the blastula, but are not the next stage in embryonic development. Once the blastula undergoes gastrulation, it will become a gastrula with three distinct layers of tissue: endoderm, mesoderm, and ectoderm.

Penicillin exerts its effect on bacterial growth through inhibition of cell-wall synthesis. This antibiotic blocks the last step in the formation of the cell wall. Glycopeptide transpeptidase is a bacterial enzyme that catalyzes the cross-linking reaction between peptidoglycan molecules, which are the main constituents of the cell wall. Penicillin inhibits the enzyme by binding covalently to its active site. The penicillin-enzyme complex cannot react further. This is an example of: A. irreversible inhibition. B. competitive inhibition. C. noncompetitive inhibition. D. uncompetitive inhibition.

Correct Answer: A. Irreversible competition. Penicillin covalently binds to the active site of the bacterial enzyme and permanently disables its action. This mode of action is inherent to irreversible inhibitors. Notice this is similar to competitive inhibitors, but competitive inhibitors are reversible and adding more substrate can overcome the competitive inhibitor.

Which reagent would you choose to convert hexan-1-ol to hexanal? A. PCC/CH2Cl2 B. DIBAL/diethyl ether C. KMnO4/aqueous H2SO4/acetone. D. K2Cr2O7/aqueous H2SO4/acetone.

Correct Answer: A. PCC/CH2Cl2. Pyridinium chlorochromate (PCC) is a mild oxidant, which converts primary and secondary alcohols to aldehydes and ketones respectively. KMnO4 and K2Cr2O7 are harsher oxidants, and would further oxidize primary alcohols to the corresponding carboxylic acids. Di-isobutylaluminum hydride (DIBAL) is a reducing agents.

An athlete runs around a 400 meter track in 60 seconds, starting and finishing at the same place. What is her speed and velocity in m/s? A. Speed = 6.67 m/s and Velocity = zero B. Speed = zero and Velocity = 6.67 m/s C. Speed = 6.67 m/s and Velocity = 6.67 m/s 360o D. Speed = 6.67 m/s and Velocity = 6.67 m/s

Correct Answer: A. Speed = 6.67 m/s and Velocity = zero Speed is a scalar quantity involving magnitude only: Speed = distance/time = 400/60 = 6.67 m/s. Velocity is a vector quantity involving both magnitude and direction: Velocity = displacement/time = 0/60 = zero. Distance traveled is not dependent on a direction, but displacement is. Displacement = distance from the finish to the start, which in this case is zero as the athlete has run around an oval to arrive back at her starting place.

Which statement below about recrystallization is NOT correct? A. The method relies on the fact that solids are more soluble in a cold solvent than they are in the same amount of hot solvent. B. Precipitation is initiated by adding a seed crystal of the compound being purified. C. Scratching the side of the vessel at the air/solution interface can induce crystal nucleation. D. Slowly cooling the solution promotes precipitation of the compound.

Correct Answer: A. The method relies on the fact that solids are more soluble in a cold solvent than they are in the same amount of hot solvent. This statement is reversed: The process of recrystallization involves dissolution of the solid in appropriate solvent at a high temperature and the subsequent re-formation of the crystals upon cooling, so that any impurities remain in solution.

Galvanizing is a process used to protect steel by applying a sacrificial coating? Which metal is used in galvanizing? A. Zinc B. Gold C. Copper D. Aluminum

Correct Answer: A. Zinc. To provide a sacrificial coating the coating metal must be more reactive than the base metal being protected. Thus gold and copper are not applicable as they are both less reactive than iron and can only provide a passive coating. Aluminum and zinc are more reactive than iron. Aluminum and zinc both form protective oxide layers that will stop corrosion of the iron, but aluminum is too reactive to be used in exposed weathering conditions. It is zinc that has just the right degree of reactivity that allows it to both protect the iron and not be corroded away, providing a strong and long lasting sacrificial coating.

Which of the following statements is NOT true regarding gastrin secretion and function? A. increased production of HCl by parietal cells stimulates gastrin secretion B. gastrin stimulates ECL cells to release histamine C. somatostatin is an inhibitor of gastrin secretion D. elevated gastric pH stimulates G cells to release gastrin.

Correct Answer: A. increased production of HCl by parietal cells acts stimulatory on gastrin secretion Gastrin stimulates parietal cells to release HCl. If A were true, then there would be a positive feedback loop where gastrin is stimulating more HCl production, and HCl is stimulating more gastrin production, causing us to burn a hole through our stomach! Increased production of HCl by parietal cells leads to somatostatin secretion, which inhibits the secretion of gastrin. Lastly, an elevated gastric pH (i.e. low amount of acid) would stimulate the G cells to release more gastrin in an attempt to stimulate the parietal cells to release more HCl to bring the acidity back to normal.

Cerebrospinal fluid (CSF) is created by special capillary networks located in the brain. CSF bathes the hollow regions of the brain, spinal cord, and around the central nervous system, within its protective coverings. The areas that the CSF pathway includes are: A. the ventricles, spinal canal, and meninges. B. the ventricles, spinal canal, and cranial nerves. C. the spinal canal, ventricles, and spinal nerves. D. the spinal canal, meninges, and cranial nerves.

Correct Answer: A. the ventricles, spinal canal, and meninges. The organs of the central nervous system (CNS), the brain and spinal cord, have hollow regions (ventricles and spinal canal, respectively). The CNS also contains the meninges, which consists of three layers of protective covering. The question states that CSF circulates in these areas. Thus A is the correct answer. The spinal nerves and cranial nerves are not part of the CNS, they are part of the peripheral nervous system (with the exception of cranial nerve II, but that's a little advanced for the MCAT).

When an electron collides with a positron (a particle with identical mass and a positive charge), the two particles are converted completely into energy; this is called an annihilation reaction. Which of the following is true immediately before the annihilation reaction? I. There is no electric field at the point halfway between the positron and the electron. II. The system is an electric dipole. III. The particles move toward each other at a constant acceleration. A. I only B. II only C. II and III only D. I, II, and III

Correct Answer: B Item II is correct because an electric dipole always exists between two identical charges of opposite magnitude. Item I is incorrect because there is always an electric field at every point in an electric dipole; though the potential may be equal to zero at certain points, the field can always be calculated. Item III is incorrect because the electrostatic force (and, consequently, the acceleration) increases as the distance between the particles decreases. Therefore, choice (B) is the correct answer.

A blood cell is placed into a salt-water mixture (70% salt). What is likely to result if the red blood cell's membrane is permeable to water? A. The cell will burst B. The cell will shrivel C. The cell will degrade D. The cell will shrivel, then expand

Correct Answer: B. The cell will shrivel. For cells with a selectively permeable membrane, water will move from higher water concentrations to lower water concentrations. In this problem, the salt is too large to cross the membrane, so the salt concentration will remain the same. Since red blood cells have more water than the salt-water mixture, the water in the cell would leave to try to make the two environments isotonic. If water leaves the cell, the cell will eventually shrink.

Mendel's second law, the Law of Independent Assortment, states that each trait assigned to offspring is done so without regard to any other trait assigned. In a dihybrid cross of two dogs, one that is black with a short tail and the other that is white with a long tail, the inheritance of one fur color is not dependent upon the inheritance of tail length. Assuming that black fur is dominant and a long tail is dominant and each parent is homozygous for each trait, how many offspring in the F2 generation will be white with a short tail?

Correct Answer: B. 1/16 F1 generation is the heterozygous offspring of the homozygous parents. F2 generation is the offspring of the heterozygous offspring generation F1. The ratio is 9:3, 3:1 in this generation, meaning that only one of the offspring will have black fur and a long tail.

The rate at which a chemical reaction occurs is dependent on many factors. Which of the following will increase the rate of reaction? A. Decreasing the temperature. B. Adding a catalyst. C. Decreasing the concentration of a reactant in solution. D. Decreasing the partial pressure of a reactant gas.

Correct Answer: B. Adding a catalyst. The rate at which a chemical reaction occurs is increased by increasing the temperature, adding a catalyst, increasing the concentration of a reactant in solution, increasing the partial pressure of a reactant gas and increasing the surface area of a reactant solid. Catalysts increase the rate of reaction by effectively lowering the Activation Energy of the reaction, thus making the reaction easy to occur under any given conditions.

In proton NMR spectroscopy, which compounds or functional groups show a characteristic peak in the range 9-10 ppm? A. halogenated alkanes B. aldehydes C. alcohols D. aromatic compounds

Correct Answer: B. Aldehydes Nuclear magnetic resonance (NMR) is concerned with the magnetic properties of certain nuclei. Anything that removes electron density from around a nucleus deshields it and shifts the absorption to higher frequency. The more electronegative the atoms that are attached to the nucleus, the higher the absorption frequency. Thus, NMR is able to provide information on the types of functional groups present as each has a characteristic chemical shift range. Aldehydes have a very characteristic shift of 9-10 ppm.

A species of desert plant secretes a chemical into the surrounding soil that kills seeds from any other species of plant that attempts to germinate in that area. What is this an example of? A. Commensalism B. Allelopathy C. Exploitation competition D. Apparent competition

Correct Answer: B. Allelopathy Allelopathy is type of INTERFERENCE competition, where the establishment of other individuals who would compete for a mutual resource is prevented, in this case using a toxic chemical. Intraspecific competition(E) occurs when competition occurs within the same species; in this case the plant is competing with all the other species of plants in the area.

What is the most correct definition of competitive inhibition? A. Another enzyme completes the same reaction and uses the available reactant B. An inhibitor binds directly to the active site and prevents the reactant from binding C. A metal cofactor prevents the binding of the reactant by binding at the active site D. An inhibitor binds to the enzyme at a binding site, and prevents the enzyme from catalyzing the reaction

Correct Answer: B. An inhibitor binds directly to the active site and prevents the reactant from binding The correct answer is B. Metal cofactors and ATP are often used to help boost enzyme activity, and are not competitive inhibitors. Non-competitive inhibition(D) occurs when an inhibitor is able to prevent the enzyme from binding with the reactant by binding to the enzyme at a site away from the active site, and change the enzyme's conformation so it cannot bind to the reactant. Competitive inhibition occurs when the inhibitor competes directly with the reactant at the active site, and this substrate takes the place of the reactant and prevents the reaction from occurring.

Which statement about the following equilibrium reaction is true? pKa=15.7 --> pKa=18 A. t-Butoxide species is stabilized by resonance B. Equilibrium favors the products. C. t-Butoxide is the dominant anionic species in the equilibrium. D. t-Butanol is the stronger acid

Correct Answer: B. Equilibrium favors the products. In an acid-base equilibrium such as this, the relative strength of an acid can be determined using the magnitude of Ka (or pKa): as Ka increases, the strength of the acid increases; as pKa (inverse log of Ka) decreases, the strength of the acid increases. The equilibrium lies to the left because t-butanol is the weaker acid compared to water. You can also think this way: hydroxide is the weaker base (more stable) compared to t-butoxide because of e- donation of alkyl groups, making the resultant anion less stable (more reactive).

People who have high blood pressure often go on low sodium diets, in which they substitute salt (NaCl) for another compound. Which of the following would be an appropriate supplementary salt? A. MgCl2 B. KCl C. BeCl2 D. SrCl2

Correct Answer: B. KCl The correct answer is B. The best substitute is one that is the closest to Na on the periodic table. Remember, families in the periodic table have similar chemical properties. Thus, anything in the second group is unacceptable, eliminating answers A, C, and D.

Which one of the following molecule is amphipathic, with both a hydrophilic and hydrophobic region? A. Starch B. Phospholipids C. Steroids D. Cholesterol

Correct Answer: B. Phospholipids The cell membrane is composed of a phospholipid bilayer that has a hydrophilic head (where the polar phosphate is attached) and a hydrophobic tail (made up of hydrocarbon chains). Starch is a polysaccharide that is generally hydrophilic and can be dissolved in water. Triglycerides, steroids and cholesterol are all entirely hydrophobic not being able to be dissolved in water. The molecule mentioned in the question is both hydrophilic and hydrophobic, indicative of the phospholipid, therefore only answer option [B] is correct.

What process is described by an animal's ability to involuntarily contract a skeletal muscle without receiving a direct signal from the brain? A. Depolarization B. Reflex Arc C. Metabolism D. Redirection

Correct Answer: B. Reflex Arc A reflex arc is a nervous system process whereby the stimulus causes a motor movement that is coordinated by the spinal cord and not the brain. Sensory neurons are able to capture the environmental stimuli and send the afferent signal to the spinal cord, which is able to send an efferent (motor) signal directly to the effector, a muscle, which then moves. Plasticity refers to the brain's ability to repair itself following damage. Metabolism is the general term defining the cell's use and production of energy. Redirection is not an accurate term and is not used in biology. Depolarization is the process of changing the cell membrane's to become more positive, commonly observed when in the nervous system with the propagation of an action potential. Therefore the correct answer is [B].

The basic premise of cladistics is organisms that are closely related share a common evolutionary history. The characteristics that are shared by group members and derived from their ancestors are called: A. Plesiomorphies B. Synapomorphies C. Apomorphies D. Autapomorphies

Correct Answer: B. Synapomorphies Plesiomorphies are characteristics that are original in the organism. While apomorhic means "derived characteristic", the prefix syn- alters the meaning to "shared derived characteristic." Using the prefix aut- causes the meaning to change to "self-derived characteristic" implying that it isn't shared by another group. Homoplasy or homoplastic characteristics are shared among groups, but weren't derived from an ancestral source.

For the Henderson-Hasselbalch equation, under what conditions would you expect the pKa of the acid to equal the pH? A. When the acid has not dissociated at all B. When the amount of conjugate base is the same as the acid C. When the acid is completely dissociated D. When the acid is a weak acid

Correct Answer: B. When the amount of conjugate base is the same as the acid For the pH to equal the pKa, log(A-/HA) must be zero, which only occurs at log(1), meaning A-/HA = 1. Thus, the amounts of acid and conjugate base would be equal. This means that roughly half of the acid has dissociated.

A high intensity peak in the mass spectrum of 2,2-dimethylpentane is observed at m/z 57. What chemical species does this peak represent? A. methyl cation B. tert-butyl carbocation C. n-propyl carbocation D. ethyl carbocation

Correct Answer: B. tert-butyl carbocation The most stable fragment likely formed from 2,2-dimethylpentane fragmentation is t-butyl species.

A construction worker uses a crane to vertically lift an object weighing 2000 N to the top of a platform at a constant rate. If it takes 30 seconds to lift the object 150 meters, what is the rate of energy consumed by the motor in the crane? A. 5.0 kW B. 8.0 kW C. 10.0 kW D. 12.0 kW

Correct Answer: C. 10 kW. We can use the equation Power = Force*velocity to solve this problem. The object moves 150 meters in 30 seconds, so the velocity must be (150m/30s) = 5 m/s. Plugging this back into the original equation of P = Fv, then P = (2000 N)(5 m/s) = 10 kW.

A horse accelerates uniformly from 0 to 20 mi/h in 2 seconds. What is the acceleration? A. 10 mi*h-1 B. 10 mi*-2 C. 10 mi*h-1*s-1 D. 10 mi*h-2

Correct Answer: C. 10 mi*h-1*s-1 The formula for acceleration is velocity divided by time: a = v/t = ((20-0) mi/h) / 2 s = 10 mi*h-1*s-1

Which of the following is closest to the bond angle of an sp2-hybridized carbon atom? A. 180 degrees B. 140 degrees C. 120 degrees D. 110 degrees

Correct Answer: C. 120 degrees An sp2-hybridized carbon has a trigonal planar geometry. This means that the bond angle will be 120 degrees, so answer choice C is the best choice. An sp-hybridized carbon has a linear geometry, meaning a bond angle of 180 degrees. Finally, an sp3-hybridized carbon has a tetrahedral geometry with bond angles of 109.5 degrees.

Three identical 12 ohm resistors are connected in parallel to a 8V battery. What is the total power dissipated in the circuit? A. 18 W B. 36 W C. 16 W D. 40 W

Correct Answer: C. 16 W When resistors are in parallel, we can find equivalent resistance simply by using the equation: (1/Req) = (1/R1) + (1/R2) + ... + (1/Rn) In this case, the equivalent resistance is: (1/Req) = (1/12)+(1/12)+(1/12)= 3/12 We find that Req = 4. We then input this into our equation for the power of a circuit P = IV = V^2/R = 8^2/4= 16W

According to the second law of thermodynamics, which of the following reactions would be favored? A. 2H2O + O2 → 2H2O2 B. ADP + Pi → ATP C. 2H2O2 → 2H2O + O2 D. 2Na + Cl2 → 2NaCl

Correct Answer: C. 2H2O2 -> 2H2O + O2 The second law of thermodynamics states that nature tends to favor a state of disorder or entropy. In other words, chemical reactions that are exergonic (release energy) and result in more products than reactants are favored. The only answer option that has more products formed in comparison to the reactants is answer option C.

Water moves through a turbine in a dam, causing it to turn. The force of the water is 300 N, and the radius of the wheel is 20 m. What is the torque around the center of the wheel? A. 60 N-m B. 600 N-m C. 6,000 N-m D. 60,000 N-m

Correct Answer: C. 6000 N-m Assuming that the water stream is tangent to the wheel, it will be perpendicular to the radius vector at the point of contact. Therefore, the torque of the force of the water stream is Torque = r*F = (20m)(300 N) = 6000 N-m.

The following statement is a description of which Gas Law? "As a gas is heated under constant pressure its volume will increase in proportion to the change in temperature." A. Dalton's law of Partial Pressures B. Boyle's gas law C. Charles's gas law D. The Ideal gas law

Correct Answer: C. Charles's gas law Charles's Law states: V T Dalton's law of Partial Pressures states: Ptotal = P1 + P2 + P3 + ... Boyle's gas law states: P 1/V The Ideal gas law states: PV = nRT

PCl3(g) + Cl2(g) -> PCl5(g); Delta(Hf) = -87.9kJ/mol A. spontaneous at all temperatures B. nonspontaneous at all temperatures C. ΔGrxn < 0 at only low temperatures D. spontaneous at only high temperatures

Correct Answer: C. Delta(Grxn) < 0 at only low temperatures On the MCAT, numbers can be intimidating, but remember that if the answer choices have no numbers in them, we should think conceptually instead of empirically. Gibbs equation helps us determine if a reaction is spontaneous or non-spontaneous. It is given as: G = H - TS In this case, the enthalpy change H is a negative number (exothermic). We know that the entropy change (S) is also negative (the products are more ordered than the reactants) because the reactants are 2 moles of gas and the products are only 1 mole of gas (a synthesis of phosphorus pentachloride). Our equation now be read differently as: G = (negative number) - temperature * (negative number) Temperature is in Kelvin and thus always a positive number, but we must consider two possibilities regarding temperature: (1) If this positive temperature is relatively low, the second part of the equation is a small positive number. Thus, if you add a small positive number to a negative number, it will probably still be negative (G<0). (2) If the positive temperature is relatively high, the second part of the equation is a large positive number. If you add a large positive number to a negative number, it will probably become positive (G>0). In both these cases, ambiguity is important because we don't know the temperature or S. The only answer that appropriately describes the case we have here is C.

What term accurately describes the structural relationship between (1R,2S)-1,2-dibromocyclopentane and (1R,2R)-1,2-dibromocyclopentane? A. Conformers B. Enantiomers C. Diastereomers D. Constitutional isomers

Correct Answer: C. Diastereomers When drawing out the structures, one can see that the basic skeletal arrangements are identical, i.e. stereoisomers (not constitutional isomers). We can dismiss conformers, since the structures cannot be interconverted exclusively by rotations about formally single bonds. The compounds are diastereomers, a class of stereoisomers that are non-superimposable, nonmirror images of one another. More specifically, the compounds are epimers: in chemistry, epimers are diastereomers that differ in configuration of only one stereogenic center.

For a very weak acid, you would expect the pH to be: a. Higher than the pKa b. Equal to the pKa c. Lower than the pKa d. Equal to double the pKa

Correct Answer: C. Lower than the pKA A weak acid will not dissociate much, meaning that A-/HA will be very low, and log(A-/HA) will be negative. Thus, a weak acid with a pKa of 10 will likely have a pH around 8 or 9

During the reaction to form ammonia from nitrogen and hydrogen according to the reaction: N2(g) + 3 H2(g) <-> 2 NH3(g), ammonia was being produced at the rate of 1.50 mol.L-1.s-1. What were the respective rates of consumption of nitrogen and hydrogen at this time? A. N2(g) 1.50 and H2(g) 1.50 mol.L-1.s-1 B. N2(g) 2.25 and H2(g) 0.75 mol.L-1.s-1 C. N2(g) 0.75 and H2(g) 2.25 mol.L-1.s-1 D. N2(g) 3.00 and H2(g) 1.00 mol.L-1.s-1

Correct Answer: C. N2(g) 0.75 and H2(g) 2.25 mol.L-1.s-1 The rate of consumption of the reactants will be the product of the rate of formation of the product multiplied by the ratio of the (co-efficient of the reactant) / (co-efficient of the product). Rate N2(g) = 1.50 x 1/2 = 0.75 mole.L-1.s-1 and H2(g) 1.50 x 3/2 = 2.25 mole.L-1.s-1.

Which layer of the epidermis is characterized by a low rate of mitosis and a high concentration of keratin? A. Stratum basale B. Stratum spinosum C. Stratum corneum D. Stratum lucidum

Correct Answer: C. Stratum corneum If a layer of epidermis has a low rate of mitosis, this indicates that the cells in this layer are not dividing very frequently. Likewise the presence of keratin, signals that the layer of epidermis must have a waterproofing function. The stratum basale is the most mitotic layer and is the bottom layer of the epidermis. As the cells are produced in the stratum basale, older cells are pushed up to the stratum spinosum, which is also high in mitotic activity. Keratin dominates in the stratum corneum, which is the most superficial layer of the epidermis, characterized by dead skin cells that are no longer undergoing mitosis. Therefore, the correct answer is [C].

Which of the following is the most accurate statement regarding the theory of Natural Selection? A. Individuals who reproduce in greater numbers are more likely to pass on their genes B. Individuals who have favorable random genetic mutations are not likely pass on their genes C. The environment can only support a finite number of individuals D. Individuals with the most genetic mutations are more likely pass on their genes

Correct Answer: C. The environment can only support a finite number of individuals The most accurate statement is C. The statement for A can be true when discussing particular reproductive strategies, however, is not true in all cases. Individuals that are best adapted to their environment will have the greatest chance to pass on their genes, not the ones that produce the most amount of offspring. If an animal produces 1000 offspring and 999 of them die, then the fitness level of that animal is very low, compared to another animal with high fitness that only produces 2 offspring and both live to pass on their genes. Statement B would be correct if it were stated oppositely, since favorable genetic mutations is what creates natural selection. Statement D is not at all accurate regarding the principles of natural selection.

Which of the following should be observed with the addition of a catalyst to a chemical reaction? A. the formation of a new product B. the consumption of the catalyst C. the activation energy is lowered D. the decrease in enthalpy

Correct Answer: C. the activation energy is lowered A catalyst speeds up a chemical reaction by lowering the activation energy of a reaction. The catalyst is never consumed, nor does it alter the reactants or products. The total enthalpy of the reaction is also not changed from what it would have been without the catalyst. Only the rate at which the reaction occurs and the activation energy is affected. The only answer option that is correct is [C].

According to the Arrhenius equation (k = Ae^-E/RT), if a reaction occurs at room temperature, what would you expect to happen if the temperature was increased by a factor of 4? A. The k value would increase by a factor of 4. B. The k value would not change. C. The k value would increase, but only slightly. D. The k value would decrease, but only slightly.

Correct Answer: C. The k value would increase, but only slightly. The correct answer is C. The Arrhenius equation is given by k = Ae^-E/RT, where A is the pre-exponential factor, R is the gas constant, T is the temperature, and E is the activation energy. Thus, if the temperature were increased by a factor of 4, then the exponent would decrease by a factor of 4, since T is in the denominator. However, since it is e^-x, the actual value won't change much. For example, exp(-1) = 0.36, but exp(-1/4) = 0.77. Thus, although the value of k will increase, it will not increase by a factor of 4, only slightly.

Organisms within the Kingdom Plantae have which of the following cellular components? a) chlorosomes b) rigid cell membrane c) vacuole d) lysosome

Correct Answer: C. Vacuole The correct answer is C. Cells within the Kingdom Plantae have chlorophyll containing cells called CHLOROPLASTS, a rigid cell WALL outside of the plasma membrane, and vacuoles that serve to store carbohydrates. Plant cells do not contain lysosomes, as other eukaryotic cells, instead they have peroxisomes for digestion of foreign material.

Which expression gives the acceleration of a 1kg mass on a frictionless inclined plane at 30o to the horizon, given that g = 9.8 m/s2? A. a = 9.8 m/s2 B. a = cos 30o x 9.8 m/s2 = 8.5 m/s2 C. a = sin 30o x 9.8 m/s2 = 4.9 m/s2 D. a = tan 30o x 9.8 m/s2 = 5.7 m/s2

Correct Answer: C. a = sin 30o x 9.8 m/s2 = 4.9 m/s2 Gravity is calculated from the vertical component of the force on the mass: sin theta = opposite/hypotenuse.

Which of the following is an example of a naturally occurring catabolic process? A. DNA replication B. photosynthesis C. cellular respiration D. protein synthesis

Correct Answer: C. cellular respiration In the cell, metabolism is defined as the chemical reactions that occur within the cell to sustain life. Metabolism can further be divided into anabolism (the synthesis of new compounds) and catabolism (breaking down of substances). Answer options A, B, D, and E are all anabolic processes, that require the use of energy to make new compounds. In cellular respiration, glucose is broken down to produce ATP, therefore this is a catabolic process.

A liquid that has stronger cohesive forces than adhesive forces would have which type of meniscus? A. flat B. concave C. convex D. parabolic

Correct Answer: C. convex. The meniscus is the curved upper surface of liquid. This is formed because of unequal cohesion and adhesion attractions. For example, in water the adhesive forces are greater than the cohesive forces, therefore the water is able to "walk up the sides" of the surface. In the case of water, a U-shaped or concave meniscus is formed. Mercury, for example has stronger cohesive attractions between the mercury molecules than adhesive attractions between the mercury and the glass surface, therefore producing a convex meniscus, which looks like an inverted U.

In a small lake, sea urchins graze upon small grasses that grow on the bottom. After the introduction of an exotic sea urchin, the small grasses became over grazed and absent. To solve the problem, a species of otter is introduced into the lake to predate upon the sea urchins, and the balance between the urchins and sea grasses is restored. What would be the appropriate term for the otter that was introduced? A. tertiary consumer B. top carnivore C. keystone predator D. primary consumer

Correct Answer: C. keystone predator The otter would be considered a SECONDARY consumer, the urchins are the primary consumers, and a hypothetical predator of the otter would be a tertiary consumer. Since the otter is responsible for preventing overgrazing of the small grasses by predating on the out of control urchin population, it is termed a keystone predator that exerts a "top-down" effect on the ecosystem.

A cell is having trouble transcribing rRNA and assembling ribosomes. Which of the following best explains this observation? A. The Golgi complex of the cell cannot produce vesicles B. The cell has mitochondria lacking a cell wall C. The cell is lacking a rough endoplasmic reticulum D. The cell has a damaged nucleolus

Correct Answer: D Mitochondria have no role in creating/transcribing rRNA which eliminates (B). While (C) may be attractive because ribosomes are associated with the Rough ER, the ER sows not transcribe rRNA. The production of vesicles is not an important function related to this question, which eliminates (A). The function of the nucleolus is to transcribe ribosomal RNA (rRNA) and combine it with proteins to form incomplete ribosomes. The nucleolus occupies up to about 25% of the volume of the cell nucleus. Because this cell cannot complete these functions, answer choice (D) is the correct answer.

The density of an unknown gas under STP conditions is 3.17 g.L-1. What is the molecular mass of the gas? A. 3.17/24.5 = 0.13 B. 3.17/22.4 = 0.14 C. 3.17 x 24.5 = 77.7 D. 3.17 x 22.4 = 71.0

Correct Answer: D. 3.17 x 22.4 = 71.0 STP is Standard Temperature and Pressure or 0oC and 1 atm pressure. At STP 1 mole of an ideal gas occupies 22.4 L. A good approximation of the molecular mass of a gas is obtained by multiplying its density in g.L-1 by 22.4 L to attain the mass of 1 mole of gas. Hence: 3.17 x 22.4 = 71.0 24.5 L is the molar volume of an ideal gas under LTP or Laboratory Temperature and Pressure, a balmy 25oC and 1 atm pressure.

An object of mass 3 kg floats motionless in a fluid of specific gravity 0.8. What is the magnitude of the buoyant force? (Use g = 10 m/s^2). A. 8 N B. 16 N C. 20 N D. 30 N

Correct Answer: D. 30N. Since the object is not moving, its acceleration must be zero, so the net force on it must also be zero. Therefore, the magnitude of the buoyant force upward must equal the magnitude of the weight downward, the specific gravity is extraneous information: B = w = mg = (3 kg)(10 N/kg) = 30 N

The velocity of nerve impulse propagation could be increased by: A. the process of nerve myelination B. decreasing nerve diameter C. increasing nerve diameter D. A and C.

Correct Answer: D. A and C During the evolution of living systems, there were two ways the velocity of nerve impulse propagation could be increased. The first way was increasing nerve diameter, while the second way was the formation of the myelin sheath. The latter mechanism is less energetically expensive than the former.

_____________ refers to the method by which an optically reactive reagent or catalyst is used to transform an optically inactive starting material into an optically active product. A. Racemization B. Enantioenrichment C. Chiral chromatography D. Asymmetric induction

Correct Answer: D. Asymmetric induction Racemization refers to the conversion of an optically active substance to a racemic form (has equal amounts of left- and right-handed enantiomers of a chiral molecule). Enantioenrichment refers to the act of enriching an already existing mixture of stereoisomers such that it contains more than 50% of one enantiomer. Chiral chromatography involves the separation of stereoisomers using a chiral stationary phase, which does not involve chemical transformations. "Optical reduction" as a technique or phrase does not exist.

Which of the following is considered the most effective laboratory sterilization technique? A. UV light exposure for 10 minutes B. Boiling at 100 °C C. Spraying of 90% ethanol D. Autoclave

Correct Answer: D. Autoclave The autoclave is the laboratory proven method for killing bacteria, fungi, and some viruses. It can reach temperatures of 121 °C and 2.7 atm, and the combined pressure and temperature are enough to kill the majority of existing pathogens. However, the autoclave cannot kill some species that are able to form heavy spores or protein coats, which include some viruses and fungi.

Pulmonary alveolus (plural form:alveoli) is an integral component of the mammalian respiratory system, which of the following characteristics describes this component? a) Actively transports O2 into the bloodstream b) Allows for gas diffusion to occur and the exchange of CO2 for O2 in the bloodstream c) Hollow cavities at the end of the respiratory tree d) B and C

Correct Answer: D. B and C The correct answer is D. Alveoli are found in the parenchyma of the lungs at the terminal end of the respiratory tree. Alveoli in the lungs of mammals are the key structure in facilitating the exchange of CO2 and O2 across the alveolar membrane by pumping CO2 rich blood from the body into the oxygen rich alveoli and allowing the exchange to occur through diffusion, not active transport.

(Fill in the blanks) Benzoic acid can be extracted into water from an organic solvent using _________ and then removed from the water into an organic solvent by the addition of _________. A. Sodium bicarbonate / sodium hydroxide B. Hydrochloric acid / sodium hydroxide C. Hydrochloric acid / sulfuric acid D. Sodium hydroxide / hydrochloric acid

Correct Answer: D. Benzoic acid, an organic compound, is insoluble in water. Extraction into water can be achieved with aqueous sodium hydroxide (deprotonation -> polar sodium benzoate, now soluble in water). Transfer of the benzoate back into organic solution is accomplished by treatment with hydrochloric acid (protonation -> less polar benzoic acid).

During the fusion stage in human fertilization, which of the following would you NOT expect to occur? A. A fusion of chromosomes from the sperm and oocyte. B. Oocyte transfers itself into a mature ovum. C. The disintegration of the flagellum and mitochondria of the sperm during the creation of the male pronucleus. D. Blending of the pronucleus from the ovum and sperm into one.

Correct Answer: D. Blending of the pronucleus from the ovum and sperm into one. The blending or fusing of the pronuclei from the oocyte and the sperm cell does not occur, in that the two do not become one. What does occur is that the protective membranes on both dissolve, allowing for the genetic material to co-mingle. A mitotic spindle is formed and attaches itself to the chromosomes from each pronucleus before the chromosomes are fully dispersed throughout the cytoplasm of the oocyte. Mitosis then takes place creating daughter cells that are genetically identical. You may remember that all of a female's eggs are arrested at meiosis II. The eggs remain in this stage until sperm fertilizes them.

Which opposite Phase Changes occur at the same temperature for a pure substance? A. Melting and sublimation B. Evaporation and boiling C. Condensation and sublimation D. Boiling and condensation

Correct Answer: D. Boiling and condensation Melting: solid to liquid and Freezing: liquid to solid occur at the Melting/Freezing Point. Boiling: liquid to gas and Condensation: gas to liquid occur at the Boiling/Condensation Point. Both evaporation: liquid to gas at the surface of the liquid and sublimation: solid to gas occur at any temperature.

Some enzymes experience a decrease in activity proportional to the concentration of their products. This phenomenon could be an example of what process? A. Feedback inhibition B. Non-competitive inhibition C. Allosteric activation D. Both A and B

Correct Answer: D. Both A and B Many cellular enzymes exhibit decreasing activity with increasing levels of reaction product. This feedback inhibition help regulate the activity of enzymatic processes. Often this process occurs through non-competitive inhibition. The product of the chemical reaction binds to the enzyme in a location other than the active site, which causes a conformational change in the enzyme and decreases enzymatic activity. Allosteric activation describes a process in which enzymatic activity is increased because of binding of some molecule to a site other than the active site.

Which of the following is the correct way to dispose of excess reagent? A. Add the excess back into the reaction. B. Return excess to the stock bottle. C. Flush down the sink with lots of water. D. Dispose in the liquid waste container.

Correct Answer: D. Dispose in the liquid waste container When dealing with excess reagent, you should never pour it back into the stock solution to avoid contamination. Unless told otherwise, it is best to only drain water in the sinks of a chemistry lab. If the reagent is toxic or flammable, leaving it in an open container is not a safe practice. Therefore, the proper way to dispose of excess chemicals is to put it in a clearly marked chemical waste container.

Which set of 1 Molar solutions has the correct pH values? A. Water pH = 0; hydrochloric acid pH = 4; acetic acid pH = 7; ammonia solution pH = 10; sodium hydroxide solution pH = 14. B. Acetic acid pH = 0; hydrochloric acid pH = 4; water pH = 7; sodium hydroxide solution pH = 10; ammonia solution pH = 14. C. Sodium hydroxide solution pH = 0; ammonia solution pH = 4; water pH = 7; acetic acid pH = 10; hydrochloric acid pH = 14. D. Hydrochloric acid pH = 0; acetic acid pH = 4; water pH = 7; ammonia solution pH = 10; sodium hydroxide solution pH = 14.

Correct Answer: D. Hydrochloric acid pH = 0; acetic acid pH = 4; water pH = 7; ammonia solution pH = 10; sodium hydroxide solution pH = 14. Acids have pH values of less than 7, with the stronger the acid the lower the pH. Bases have pH values of greater than 7, with the stronger the base the higher the pH. Typically: Strong acids have a pH of 0 or less, hydrochloric acid pH = 0. Weak acids between pH 3-6, acetic acid pH = 4. Neutral solutions have pH = 7, water pH = 7. Weak bases have a pH 8-10, ammonia solution pH = 10. Strong bases have a pH of 14 or more, sodium hydroxide solution pH = 14.

Which of the following disorders is a mistake that occurred during meiosis, which resulted in a trisomy of the sex chromosome? A) Kawasaki Disease B) Ketoacidosis C) Down Syndrome D) Klinefelter Syndrome

Correct Answer: D. Klinefelter Syndrome Klinefelter syndrome is a result of an extra X chromosome in men. The syndrome is normally not diagnosed until after puberty, and its outward symptoms are mild. Generally, men are diagnosed when they seek treatment for symptoms of other diseases or infertility.

What happens to the kinetic energy of a race car if its speed is tripled? A. The kinetic energy increases 3 times its original value. B. The kinetic energy increases 4.5 times its original value. C. The kinetic energy increases 6 times its original value. D. The kinetic energy increases 9 times its original value.

Correct Answer: D. The kinetic energy increases to 9 times its original value. Kinetic energy is: KE = (1/2)mv2. The kinetic energy is directly proportional to the square of the velocity (or speed). If the speed is multiplied by 3 (tripled), the KE must be multiplied by 32 = 9. Sidenote, race car spelled backwards is still race car.

A student creates a 1M citrate (C3H5O(COO)33-) buffer solution at pH 5.0. He then dilutes the solution to 200 mM, and adds it to his experiment. What is the pH of the 200 mM buffer solution? A. Between pH 5 and pH 7 B. Greater than pH 7 C. Less than pH 5 D. The pH will remain close to 5

Correct Answer: D. The pH will remain close to 5. Buffers are designed to maintain pH at a certain level, and operate through the complementation of a conjugate acid and base. As long as the ratios of acid and base remain the same in the buffer system, and they will no matter what the dilution, as long as the dilution is not very very small (i.e. 1 mM or less), the pH will remain the same.

When metallic substances lose electrons, they are trying to achieve the electron configuration of what? A. The metal immediately before it on the periodic table. B. The metal immediately after it on the periodic table. C. The nearest halogen. D. The previous noble gas.

Correct Answer: D. The previous noble gas. A metal prefers to lose electrons so that it has the configuration of 8 around its valence shell so that it is equivalent to the stable noble gas previous to it.

In the phrase "SN1 Reaction", what does the "1" indicate? A. The equilibrium constant. B. The number of reactants involved. C. The stereochemical outcome. D. The rate order.

Correct Answer: D. The rate order. "SN" stands for nucleophilic substitution and the "1″ represents the fact that the rate-determining step is unimolecular.

A racecar travels in a circular path around the Daytona 500 track. The radius of the circular track is doubled and the speed of the car does not change. The required force to maintain the car's motion is: A. quadrupled. B. unchanged. C. doubled. D. halved.

Correct Answer: D. halved. The centripetal force of the car is mv2/r, where m is the car's mass, v is the velocity, and r is the radius of the circular track. If we double the radius while keeping everything else uniform, the centripetal force will be halved because they are inversely proportional.

Genetic drift is the process responsible for: A. gaining a new allele within large populations. B. gaining a new allele within sufficiently small populations. C. losing an existing allele due to emigration. D. losing an existing allele due to random sampling.

Correct Answer: D. losing an existing allele due to random sampling. Genetic drift represents the change in an allele frequency in a population due to random sampling. Influence from genetic drift is particularly important in small populations. The random changes in allele frequencies could result in the elimination of an existing allele from a population.

Which of the following is NOT needed to calculate the endpoint of a titration? A. Initial volume of titrant B. Final volume of titrant C. Concentration of the titrant D. pH of the titrant

Correct Answer: D. pH of the titrant During a titration procedure, a buret is lowered into a clean Erlenmeyer flask. The initial volume of titrant is recorded and a stream of titrant is delivered while constantly mixing the sample solution. Once the pH indicator changes colors we have reached the endpoint. The final volume is recorded and used in conjunction with the initial volume to find the volume of titrant used, and along with the concentration of the titrant to find how many moles of titrant were used. Finally, we can use stoichiometry of the titration reaction to calculate the number of moles of reactant in our solution. The pH of the titrant is not needed.

Pulmonary alveolus (plural form:alveoli) is an integral component of the mammalian respiratory system, which of the following characteristics describes this component? a) Actively transports O2 into the bloodstream b) Allows for gas diffusion to occur and the exchange of CO2 for O2 in the bloodstream c) Hollow cavities at the end of the respiratory tree d) B and C

The correct answer is D. Alveoli are found in the parenchyma of the lungs at the terminal end of the respiratory tree. Alveoli in the lungs of mammals are the key structure in facilitating the exchange of CO2 and O2 across the alveolar membrane by pumping CO2 rich blood from the body into the oxygen rich alveoli and allowing the exchange to occur through diffusion, not active transport.

In the species of violet Viola granulanica, the allele Y is responsible for pigmentation of the petals and the allele X is responsible for petal shape. The dominant allele Y creates a red pigmentation in the petals, and a homozygous recessive pair of this allele will result in blue petals. The dominant allele X creates pointed petals, and a homozygous recessive pair of this allele will result in rounded petals. If a flower with the alleles YyXX and a flower with the alleles YyXx breed, what percent of the offspring will have blue-pointed petals? A. 0% B. 25% C. 33% D. 50%

The resulting progeny will have 4 violets with blue-pointed petals out of a total of 16 possible combinations. If we generate a Punnet Square, we can lay out the alleles in the genetic cross. As we can see, there are 16 combinations possible, 12 of which result in red-pointed petals and 4 of which result in blue-pointed petals. There are no combinations featuring rounded petals, because the first flower did not contain any recessive alleles for X, and therefore all the resulting progeny in the cross have pointed petals.