MCAT Official Prep Free Practice
Exam-Graded A
What quantity of Compound 1 must be provided to prepare 100.00 mL of solution with a
concentration equal to Ki? Ki = 60.3 μM
A.48.4 mg
B.24.2 mg
C. 5.64 mg
D. 2.92 mg - ANS-In 100.00 mL solution, 60.3 μM Compound 1 contains 6.03 μmol,
which when converted to mol and multiplied by the molar mass, yields 0.00292 g or
2.92 mg.
If only [I] is increased, then [ESI] or [EI] increases. This is an example of:
A.
the Bose-Einstein Principle.
B.
the Heisenberg Uncertainty Principle.
C.
the Le Châtelier's Principle.
D.
the Pauli Exclusion Principle. - ANS-Le Châtelier's Principle states that in a reversible
process, the application of stress to the system will cause the system to respond in a
way that will relieve this stress. In this case, the reversible process is E + I forming EI or
ES + I forming ESI. In either case, increasing [I] induces stress of the system, and the
system relieves that stress by converting I to either more EI or ESI.
Which structural change to Compound 1 would make it more water soluble?
A.
Replacing benzene CH with N in the ring
B.
Replacing C=O with C=CH2
C.
Replacing N-N=N with CH-CH=CH
D.
Replacing NH with NCH3 - ANS-Nitrogen in the benzene ring would have a lone pair
that could accept a hydrogen bond from water, thus increasing the solubility of the
compound.
In μM•s-1 and μM, what should the approximate values of kcat/KM and Ki be,
respectively, when [I] = 180 μM?
,A.
33.5 and 15.7
B.
75 and 30.1
C.
150 and 60.3
D.
300 and 120.6 - ANS-Based on the data in Table 1, increasing [I] has no effect on
kcat/KM, so it should remain at 150 μM•s-1. Also, Ki is an equilibrium constant, so it will
not be affected by a change in [I].
What functional group transformation occurs in the product of the reaction catalyzed by
Na+-NQR?
A.
RC(=O)R → RCH(OH)R
B.
ROPO32- → ROH + Pi
C.
RC(=O)NHR'→ RCOOH + R'NH2
D.
RC(=O)OR'→ RCOOH + R'OH - ANS-This is two-electron reduction of a ketone to an
alcohol, which is the reaction catalyzed by Na+-NQR.
What is the ratio of cation to enzyme in the spectroelectrochemical experiments
described in the passage?
A.
1:2
B.
2:1
C.
20:1
D.
200:1 - ANS-The ratio can be found by noting that the enzyme concentration was 0.75
mM, while the concentration of cations was 0.150 M = 150 mM. The ratio is therefore
200:1.
The reaction between NADH and ubiquinone is exergonic, but the reaction, when
catalyzed by Na+-NQR, does not generate much heat in vivo. What factor accounts for
this difference?
The reaction catalyzed by Na+-NQR in vivo:
A.
is more exothermic as a result of the lower activation energy.
B.
occurs sequentially in several small steps.
C.
maintains a large separation between the reacting centers.
,D.
is coupled to the movement of a charged particle against a concentration gradient. -
ANS-The movement of a charged particle against its concentration gradient is
energetically costly. Coupling the two processes: the redox reaction between NADH and
ubiquinone and the movement of Na+ up a concentration gradient makes the overall
process less exothermic.
Two open flasks I and II contain different volumes of the same liquid. Suppose that the
pressure is measured at a point 10 cm below the surface of the liquid in each container.
How will the pressures compare?
A.
The pressures will be equal.
B.
Pressure in flask I will be less.
C.
Pressure in flask II will be less.
D.
The pressures cannot be compared from the information given. - ANS-The pressure at
a point 10 cm below the surface of the liquid is the same in both flasks because the
pressure is equal to the liquid density multiplied by the gravitational acceleration
multiplied by 10 cm.
What is the identity of an atom that contains six protons and eight neutrons?
A.
Nitrogen
B.
Carbon
C.
Oxygen
D.
Silicon - ANS-Carbon contains six protons because it also contains six electrons as a
neutral atom.
Which of the following substances is polar?
A.
NF3
B.
CCl4
C.
CO2
D.
Li2 - ANS-The geometry of trifluoroamine is impacted by the lone pair on nitrogen,
making it trigonal pyramidal. No bond dipoles cancel; this results in a polar molecule.
If all else is held constant, which of the following changes would NOT double the
volume of a gas?
, A.
Doubling the pressure
B.
Doubling the absolute temperature
C.
Halving the pressure
D.
Doubling the number of gas molecules - ANS-Based on Boyle's Law, P is inversely
proportional to volume, thus, doubling the pressure of a gas sample will decrease, not
increase, the volume.
What is the number of neutrons in the nucleus of the atom used to produce laser
radiations?
A.
48
B.
49
C.
50
D.
51 - ANS-The 8636Kr atom contains 36 electrons and 36 protons. Therefore, the
number of protons is equal to 86 - 36 = 50 neutrons.
What is the molecular formula of the heterocyclic aromatic compound pyrrole?
A.
C2H3N
B.
C4H5N
C.
C6H7N
D.
C8H9N - ANS-This is the molecular formula of pyrrole, a five-membered aromatic
heterocycle containing one nitrogen atom.
Approximately how many moles of Kr+ are contained in the laser tube at 0°C and 1
atm?
A.
3 x 10-7
B.
2 x 10-6
C.
4 x 10-5
D.
5 x 10-4 - ANS-There is 1 mole of gas in a volume of 22.4 L = 2.24 x 104 cm3 at STP;
there are approximately 5 x 10-4 moles in 11 cm3.
Exam-Graded A
What quantity of Compound 1 must be provided to prepare 100.00 mL of solution with a
concentration equal to Ki? Ki = 60.3 μM
A.48.4 mg
B.24.2 mg
C. 5.64 mg
D. 2.92 mg - ANS-In 100.00 mL solution, 60.3 μM Compound 1 contains 6.03 μmol,
which when converted to mol and multiplied by the molar mass, yields 0.00292 g or
2.92 mg.
If only [I] is increased, then [ESI] or [EI] increases. This is an example of:
A.
the Bose-Einstein Principle.
B.
the Heisenberg Uncertainty Principle.
C.
the Le Châtelier's Principle.
D.
the Pauli Exclusion Principle. - ANS-Le Châtelier's Principle states that in a reversible
process, the application of stress to the system will cause the system to respond in a
way that will relieve this stress. In this case, the reversible process is E + I forming EI or
ES + I forming ESI. In either case, increasing [I] induces stress of the system, and the
system relieves that stress by converting I to either more EI or ESI.
Which structural change to Compound 1 would make it more water soluble?
A.
Replacing benzene CH with N in the ring
B.
Replacing C=O with C=CH2
C.
Replacing N-N=N with CH-CH=CH
D.
Replacing NH with NCH3 - ANS-Nitrogen in the benzene ring would have a lone pair
that could accept a hydrogen bond from water, thus increasing the solubility of the
compound.
In μM•s-1 and μM, what should the approximate values of kcat/KM and Ki be,
respectively, when [I] = 180 μM?
,A.
33.5 and 15.7
B.
75 and 30.1
C.
150 and 60.3
D.
300 and 120.6 - ANS-Based on the data in Table 1, increasing [I] has no effect on
kcat/KM, so it should remain at 150 μM•s-1. Also, Ki is an equilibrium constant, so it will
not be affected by a change in [I].
What functional group transformation occurs in the product of the reaction catalyzed by
Na+-NQR?
A.
RC(=O)R → RCH(OH)R
B.
ROPO32- → ROH + Pi
C.
RC(=O)NHR'→ RCOOH + R'NH2
D.
RC(=O)OR'→ RCOOH + R'OH - ANS-This is two-electron reduction of a ketone to an
alcohol, which is the reaction catalyzed by Na+-NQR.
What is the ratio of cation to enzyme in the spectroelectrochemical experiments
described in the passage?
A.
1:2
B.
2:1
C.
20:1
D.
200:1 - ANS-The ratio can be found by noting that the enzyme concentration was 0.75
mM, while the concentration of cations was 0.150 M = 150 mM. The ratio is therefore
200:1.
The reaction between NADH and ubiquinone is exergonic, but the reaction, when
catalyzed by Na+-NQR, does not generate much heat in vivo. What factor accounts for
this difference?
The reaction catalyzed by Na+-NQR in vivo:
A.
is more exothermic as a result of the lower activation energy.
B.
occurs sequentially in several small steps.
C.
maintains a large separation between the reacting centers.
,D.
is coupled to the movement of a charged particle against a concentration gradient. -
ANS-The movement of a charged particle against its concentration gradient is
energetically costly. Coupling the two processes: the redox reaction between NADH and
ubiquinone and the movement of Na+ up a concentration gradient makes the overall
process less exothermic.
Two open flasks I and II contain different volumes of the same liquid. Suppose that the
pressure is measured at a point 10 cm below the surface of the liquid in each container.
How will the pressures compare?
A.
The pressures will be equal.
B.
Pressure in flask I will be less.
C.
Pressure in flask II will be less.
D.
The pressures cannot be compared from the information given. - ANS-The pressure at
a point 10 cm below the surface of the liquid is the same in both flasks because the
pressure is equal to the liquid density multiplied by the gravitational acceleration
multiplied by 10 cm.
What is the identity of an atom that contains six protons and eight neutrons?
A.
Nitrogen
B.
Carbon
C.
Oxygen
D.
Silicon - ANS-Carbon contains six protons because it also contains six electrons as a
neutral atom.
Which of the following substances is polar?
A.
NF3
B.
CCl4
C.
CO2
D.
Li2 - ANS-The geometry of trifluoroamine is impacted by the lone pair on nitrogen,
making it trigonal pyramidal. No bond dipoles cancel; this results in a polar molecule.
If all else is held constant, which of the following changes would NOT double the
volume of a gas?
, A.
Doubling the pressure
B.
Doubling the absolute temperature
C.
Halving the pressure
D.
Doubling the number of gas molecules - ANS-Based on Boyle's Law, P is inversely
proportional to volume, thus, doubling the pressure of a gas sample will decrease, not
increase, the volume.
What is the number of neutrons in the nucleus of the atom used to produce laser
radiations?
A.
48
B.
49
C.
50
D.
51 - ANS-The 8636Kr atom contains 36 electrons and 36 protons. Therefore, the
number of protons is equal to 86 - 36 = 50 neutrons.
What is the molecular formula of the heterocyclic aromatic compound pyrrole?
A.
C2H3N
B.
C4H5N
C.
C6H7N
D.
C8H9N - ANS-This is the molecular formula of pyrrole, a five-membered aromatic
heterocycle containing one nitrogen atom.
Approximately how many moles of Kr+ are contained in the laser tube at 0°C and 1
atm?
A.
3 x 10-7
B.
2 x 10-6
C.
4 x 10-5
D.
5 x 10-4 - ANS-There is 1 mole of gas in a volume of 22.4 L = 2.24 x 104 cm3 at STP;
there are approximately 5 x 10-4 moles in 11 cm3.
