Page 1 of 79
LEHNINGER PRINCIPLES OF BIOCHEMISTRY EXAM PREP 2026
QUESTIONS WITH VERIFIED ANSWERS DETAILED RATIONALES GRADED
A+
Part I: Water, pH, and Buffers (Questions 1–30)
1. Which property of water is most directly responsible for its high boiling point
and high surface tension?
A. Its low molecular weight
B. Extensive hydrogen bonding between water molecules
C. Its nonpolar covalent bonds
D. Its ability to act as a buffer
Rationale: Water’s extensive hydrogen bonding network requires significant
energy to disrupt, producing unusually high boiling point, surface tension, and
heat of vaporization.
2. The ion product of water (Kw) at 25°C is which of the following?
A. 1 × 10⁻⁷
B. 1 × 10⁻¹⁴
C. 1 × 10⁻¹
D. 1 × 10⁰
Rationale: Kw = [H⁺][OH⁻] = 1 × 10⁻¹⁴ at 25°C, forming the basis of the pH scale.
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3. A solution with a pH of 3 has a hydrogen ion concentration of which of the
following?
A. 3 M
B. 1 × 10⁻³ M
C. 1 × 10³ M
D. 3 × 10⁻³ M
Rationale: pH = −log[H⁺], so pH 3 corresponds to [H⁺] = 10⁻³ M.
4. The Henderson–Hasselbalch equation is used to do which of the following?
A. Calculate the molecular weight of a protein
B. Relate pH, pKa, and the ratio of conjugate base to acid
C. Determine enzyme velocity
D. Measure membrane fluidity
Rationale: pH = pKa + log([A⁻]/[HA]) relates pH to the ionization state of a weak
acid, essential for buffer calculations.
5. A buffer is most effective when the pH is within which range relative to its pKa?
A. More than 3 units above the pKa
B. Within approximately ±1 pH unit of the pKa
C. Exactly at pH 7.0 regardless of pKa
D. More than 3 units below the pKa
Rationale: Buffering capacity is maximal near the pKa and remains effective within
roughly ±1 pH unit.
6. Which of the following is the primary physiological buffer system in blood?
A. Phosphate buffer
B. Bicarbonate buffer system
C. Acetate buffer
D. Tris buffer
Rationale: The carbonic acid–bicarbonate system is the major extracellular buffer,
linked to respiratory and renal regulation.
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7. The pKa of acetic acid is 4.76. At pH 5.76, the ratio of acetate to acetic acid is
which of the following?
A. 1:1
B. 10:1
C. 1:10
D. 100:1
Rationale: pH − pKa = 1, so log([A⁻]/[HA]) = 1, meaning the ratio is 10:1.
8. Which of the following best describes the hydrophobic effect?
A. The tendency of nonpolar molecules to aggregate in water, driven by entropy
B. The repulsion of water by nonpolar molecules
C. The attraction of nonpolar molecules to water
D. The formation of hydrogen bonds between nonpolar groups
Rationale: The hydrophobic effect arises because nonpolar surfaces disrupt
water’s hydrogen-bond network; aggregation minimizes this disruption, increasing
entropy.
9. Osmotic pressure is best described as which of the following?
A. The pressure required to prevent net water movement across a
semipermeable membrane
B. The pressure exerted by a gas
C. The pressure of a solid on a surface
D. The pressure of a solution on its container
Rationale: Osmotic pressure opposes water movement driven by solute
concentration differences across a semipermeable membrane.
10. Which of the following is a weak interaction that stabilizes protein structure?
A. Hydrogen bonds
B. Covalent peptide bonds only
C. Disulfide bonds only
D. Ionic bonds only
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Rationale: Hydrogen bonds, hydrophobic interactions, van der Waals forces, and
ionic interactions are weak interactions that collectively stabilize protein structure.
11. The pH of a 0.01 M solution of a strong acid is which of the following?
A. 1
B. 2
C. 7
D. 12
Rationale: A strong acid fully dissociates, so [H⁺] = 0.01 M = 10⁻² M, giving pH 2.
12. Which of the following statements about water is true?
A. Water is a nonpolar solvent.
B. Water is an excellent solvent for ionic and polar substances.
C. Water has a low dielectric constant.
D. Water cannot form hydrogen bonds.
Rationale: Water’s high polarity and dielectric constant make it an excellent
solvent for charged and polar solutes.
13. The pKa of a weak acid is 6.0. At pH 6.0, which of the following is true?
A. The acid is fully protonated.
B. The concentrations of acid and conjugate base are equal.
C. The acid is fully deprotonated.
D. The solution is not buffered.
Rationale: At pH = pKa, [HA] = [A⁻], and the buffer is at its maximum capacity.
14. Which of the following contributes most to the high heat capacity of water?
A. Its low density
B. Hydrogen bonding
C. Its nonpolar bonds
D. Its low viscosity
Rationale: Breaking hydrogen bonds requires significant energy, giving water a
high heat capacity that stabilizes temperature.
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LEHNINGER PRINCIPLES OF BIOCHEMISTRY EXAM PREP 2026
QUESTIONS WITH VERIFIED ANSWERS DETAILED RATIONALES GRADED
A+
Part I: Water, pH, and Buffers (Questions 1–30)
1. Which property of water is most directly responsible for its high boiling point
and high surface tension?
A. Its low molecular weight
B. Extensive hydrogen bonding between water molecules
C. Its nonpolar covalent bonds
D. Its ability to act as a buffer
Rationale: Water’s extensive hydrogen bonding network requires significant
energy to disrupt, producing unusually high boiling point, surface tension, and
heat of vaporization.
2. The ion product of water (Kw) at 25°C is which of the following?
A. 1 × 10⁻⁷
B. 1 × 10⁻¹⁴
C. 1 × 10⁻¹
D. 1 × 10⁰
Rationale: Kw = [H⁺][OH⁻] = 1 × 10⁻¹⁴ at 25°C, forming the basis of the pH scale.
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3. A solution with a pH of 3 has a hydrogen ion concentration of which of the
following?
A. 3 M
B. 1 × 10⁻³ M
C. 1 × 10³ M
D. 3 × 10⁻³ M
Rationale: pH = −log[H⁺], so pH 3 corresponds to [H⁺] = 10⁻³ M.
4. The Henderson–Hasselbalch equation is used to do which of the following?
A. Calculate the molecular weight of a protein
B. Relate pH, pKa, and the ratio of conjugate base to acid
C. Determine enzyme velocity
D. Measure membrane fluidity
Rationale: pH = pKa + log([A⁻]/[HA]) relates pH to the ionization state of a weak
acid, essential for buffer calculations.
5. A buffer is most effective when the pH is within which range relative to its pKa?
A. More than 3 units above the pKa
B. Within approximately ±1 pH unit of the pKa
C. Exactly at pH 7.0 regardless of pKa
D. More than 3 units below the pKa
Rationale: Buffering capacity is maximal near the pKa and remains effective within
roughly ±1 pH unit.
6. Which of the following is the primary physiological buffer system in blood?
A. Phosphate buffer
B. Bicarbonate buffer system
C. Acetate buffer
D. Tris buffer
Rationale: The carbonic acid–bicarbonate system is the major extracellular buffer,
linked to respiratory and renal regulation.
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,Page 3 of 79
7. The pKa of acetic acid is 4.76. At pH 5.76, the ratio of acetate to acetic acid is
which of the following?
A. 1:1
B. 10:1
C. 1:10
D. 100:1
Rationale: pH − pKa = 1, so log([A⁻]/[HA]) = 1, meaning the ratio is 10:1.
8. Which of the following best describes the hydrophobic effect?
A. The tendency of nonpolar molecules to aggregate in water, driven by entropy
B. The repulsion of water by nonpolar molecules
C. The attraction of nonpolar molecules to water
D. The formation of hydrogen bonds between nonpolar groups
Rationale: The hydrophobic effect arises because nonpolar surfaces disrupt
water’s hydrogen-bond network; aggregation minimizes this disruption, increasing
entropy.
9. Osmotic pressure is best described as which of the following?
A. The pressure required to prevent net water movement across a
semipermeable membrane
B. The pressure exerted by a gas
C. The pressure of a solid on a surface
D. The pressure of a solution on its container
Rationale: Osmotic pressure opposes water movement driven by solute
concentration differences across a semipermeable membrane.
10. Which of the following is a weak interaction that stabilizes protein structure?
A. Hydrogen bonds
B. Covalent peptide bonds only
C. Disulfide bonds only
D. Ionic bonds only
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Rationale: Hydrogen bonds, hydrophobic interactions, van der Waals forces, and
ionic interactions are weak interactions that collectively stabilize protein structure.
11. The pH of a 0.01 M solution of a strong acid is which of the following?
A. 1
B. 2
C. 7
D. 12
Rationale: A strong acid fully dissociates, so [H⁺] = 0.01 M = 10⁻² M, giving pH 2.
12. Which of the following statements about water is true?
A. Water is a nonpolar solvent.
B. Water is an excellent solvent for ionic and polar substances.
C. Water has a low dielectric constant.
D. Water cannot form hydrogen bonds.
Rationale: Water’s high polarity and dielectric constant make it an excellent
solvent for charged and polar solutes.
13. The pKa of a weak acid is 6.0. At pH 6.0, which of the following is true?
A. The acid is fully protonated.
B. The concentrations of acid and conjugate base are equal.
C. The acid is fully deprotonated.
D. The solution is not buffered.
Rationale: At pH = pKa, [HA] = [A⁻], and the buffer is at its maximum capacity.
14. Which of the following contributes most to the high heat capacity of water?
A. Its low density
B. Hydrogen bonding
C. Its nonpolar bonds
D. Its low viscosity
Rationale: Breaking hydrogen bonds requires significant energy, giving water a
high heat capacity that stabilizes temperature.
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