Title: MCAT Original Practice-2 - 80 MCQ Cards / Chemical and Physical Foundations of Biological Systems
Tags: chemical mcat practice2

Question: A weak monoprotic acid is titrated with strong base. At the labeled half-equivalence point, which relationship is most accurate?
Explanation: Correct: A. At half-equivalence, the acid and conjugate base concentrations are equal, so the Henderson–Hasselbalch equation reduces to pH = pKa.
Difficulty: Easy
Other fields (not shown on cards):
Choices: pH = pKa
pH = 7.00 for all weak acids
[HA] is ten times [A−]
The solution contains only conjugate base
Correct: A

Question: In the circuit shown, what is the current through a single 6 Ω resistor connected to a 12 V battery?
Explanation: Correct: B. Ohm's law gives I = V/R = 12/6 = 2 A.
Difficulty: Easy
Other fields (not shown on cards):
Choices: 0.5 A
2 A
6 A
72 A
Correct: B

Question: A compound has a molecular ion peak at m/z 88 and a strong broad IR absorption from 2500–3300 cm⁻¹. Which functional group is most strongly suggested?
Explanation: Correct: B. A very broad 2500–3300 cm⁻¹ band is characteristic of the O–H stretch of a carboxylic acid.
Difficulty: Medium
Other fields (not shown on cards):
Choices: Alcohol
Carboxylic acid
Alkyne
Ketone only
Correct: B

Question: A buffer is made from 0.20 M NH3 and 0.10 M NH4Cl. If pKa(NH4+) = 9.25, what is the approximate pH?
Explanation: Correct: C. pH = pKa + log(base/acid) = 9.25 + log(2) ≈ 9.55.
Difficulty: Medium
Other fields (not shown on cards):
Choices: 8.95
9.25
9.55
10.25
Correct: C

Question: A student doubles the absolute temperature of an ideal gas while holding volume and moles constant. What happens to pressure?
Explanation: Correct: C. From PV = nRT, at constant n and V, pressure is directly proportional to absolute temperature.
Difficulty: Easy
Other fields (not shown on cards):
Choices: It halves
It stays constant
It doubles
It quadruples
Correct: C

Question: A lens forms a real, inverted image when an object is placed outside its focal length. Which type of lens is most consistent with this observation?
Explanation: Correct: B. A converging lens can form real inverted images when the object is beyond the focal point.
Difficulty: Easy
Other fields (not shown on cards):
Choices: Diverging lens
Converging lens
Plane glass only
Opaque aperture
Correct: B

Question: In the refraction diagram, the ray bends toward the normal when entering the lower medium. Which conclusion follows?
Explanation: Correct: B. Light bends toward the normal when it enters a medium in which it travels more slowly, corresponding to a higher refractive index.
Difficulty: Medium
Other fields (not shown on cards):
Choices: The lower medium has a smaller refractive index
The lower medium has a larger refractive index
The frequency of light becomes zero
The speed of light increases in the lower medium
Correct: B

Question: A 2 kg object accelerates at 3 m/s² on a frictionless surface. What is the net force?
Explanation: Correct: C. Newton's second law gives F = ma = 2 × 3 = 6 N.
Difficulty: Easy
Other fields (not shown on cards):
Choices: 1.5 N
5 N
6 N
9 N
Correct: C

Question: A reaction has ΔG < 0 but proceeds very slowly at room temperature. Which statement best explains this?
Explanation: Correct: B. A negative ΔG indicates thermodynamic favorability, but rate depends on activation energy.
Difficulty: Medium
Other fields (not shown on cards):
Choices: The reaction is thermodynamically unfavorable
The activation energy may be high
The equilibrium constant must be zero
Entropy must be negative
Correct: B

Question: Which substitution would most increase the acidity of acetic acid?
Explanation: Correct: A. An electron-withdrawing fluorine stabilizes the conjugate base by induction, increasing acidity.
Difficulty: Medium
Other fields (not shown on cards):
Choices: Replacing a methyl hydrogen with fluorine
Replacing the carbonyl oxygen with sulfur
Adding a second methyl group
Converting it to an ester
Correct: A

Question: A radioactive tracer has a half-life of 6 hours. What fraction remains after 18 hours?
Explanation: Correct: D. Eighteen hours is three half-lives, so the remaining fraction is (1/2)^3 = 1/8.
Difficulty: Easy
Other fields (not shown on cards):
Choices: 1/2
1/3
1/6
1/8
Correct: D

Question: A gas expands adiabatically and does work on the surroundings. Which change is expected for the gas?
Explanation: Correct: B. In adiabatic expansion, q = 0. Work done by the gas lowers internal energy and often temperature.
Difficulty: Hard
Other fields (not shown on cards):
Choices: Temperature increases because heat enters
Temperature decreases because internal energy is used for work
Temperature is fixed by definition
Pressure must become infinite
Correct: B

Question: Which molecule would be expected to have the highest boiling point?
Explanation: Correct: C. Ethanol can donate and accept hydrogen bonds, giving stronger intermolecular forces than the other options.
Difficulty: Easy
Other fields (not shown on cards):
Choices: Ethane
Dimethyl ether
Ethanol
Propane
Correct: C

Question: A peptide is run through an ion-exchange column containing negatively charged beads at pH 7. Which peptide will bind most strongly?
Explanation: Correct: D. Negatively charged resin binds positively charged peptides; stronger positive charge generally increases binding.
Difficulty: Medium
Other fields (not shown on cards):
Choices: Net charge −2
Net charge 0
Net charge +1
Net charge +4
Correct: D

Question: In a mass spectrometer, two singly charged ions have the same kinetic energy. Ion X has twice the mass of ion Y. How does X's speed compare to Y's?
Explanation: Correct: C. K = 1/2 mv². At equal kinetic energy, v is inversely proportional to √m.
Difficulty: Hard
Other fields (not shown on cards):
Choices: X is twice as fast
X is the same speed
X is 1/√2 as fast
X is half as fast
Correct: C

Question: A solution of a pure enantiomer is diluted with solvent that has no optical activity. What happens to observed rotation in the same tube length?
Explanation: Correct: B. Observed rotation is proportional to concentration and path length.
Difficulty: Medium
Other fields (not shown on cards):
Choices: It increases
It decreases in magnitude
It changes sign
It becomes independent of concentration
Correct: B

Question: Which event directly increases the frequency of a sound wave heard by a stationary observer?
Explanation: Correct: A. The Doppler effect increases observed frequency when source and observer approach each other.
Difficulty: Easy
Other fields (not shown on cards):
Choices: Source moving toward the observer
Source moving away from the observer
Lowering the wave amplitude
Moving the sound into vacuum
Correct: A

Question: A current-carrying wire is placed in a magnetic field parallel to the wire. What is the magnetic force on the wire?
Explanation: Correct: B. Magnetic force on a current-carrying wire is F = ILB sinθ; θ = 0° gives zero force.
Difficulty: Medium
Other fields (not shown on cards):
Choices: Maximum
Zero
Equal to qE
Always downward
Correct: B

Question: A researcher wants to separate two proteins with similar mass but different isoelectric points. Which technique is most directly suited?
Explanation: Correct: A. Isoelectric focusing separates proteins based on pI in a pH gradient.
Difficulty: Medium
Other fields (not shown on cards):
Choices: Isoelectric focusing
Size-exclusion chromatography only
Simple distillation
Gas chromatography
Correct: A

Question: A reaction rate doubles when enzyme concentration doubles, while substrate is saturating. Which inference is best?
Explanation: Correct: B. At saturating substrate, rate approaches Vmax, and Vmax is proportional to active enzyme concentration.
Difficulty: Medium
Other fields (not shown on cards):
Choices: The enzyme is denatured
Vmax increased
Km doubled
The reaction became nonenzymatic
Correct: B