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CHEM 210 BIOCHEMISTRY EXAM WITH VERIFIED
ANSWERS DETAILED RATIONALES GRADED A+
CHEM 210 Biochemistry — Module 1 to 8 Exams
SECTION 1: WATER, pH & BUFFERS (Questions 1–30)
1. Which property of water allows it to dissolve ionic compounds?
A. Low dielectric constant
B. High dielectric constant and ability to form hydrogen bonds
C. Low specific heat
D. Nonpolar nature
Rationale: Water has a high dielectric constant, which reduces the electrostatic attraction
between ions, and it forms hydrogen bonds with ions, stabilizing them in solution. This makes
water an excellent solvent for ionic compounds.
2. The pH of a solution with [H⁺] = 1 × 10⁻⁴ M is:
A. 4
B. 10
C. 1
D. 14
Rationale: pH = −log[H⁺] = −log(1 × 10⁻⁴) = 4. The pH scale is logarithmic and inversely related to
hydrogen ion concentration.
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3. What is the pH of a 0.01 M solution of HCl?
A. 1
B. 2
C. 12
D. 0.01
Rationale: HCl is a strong acid that completely dissociates. [H⁺] = 0.01 M = 1 × 10⁻² M. pH =
−log(10⁻²) = 2.
4. The Henderson-Hasselbalch equation is:
A. pH = pKa + log([A⁻]/[HA])
B. pH = pKa − log([A⁻]/[HA])
C. pH = pKa + log([HA]/[A⁻])
D. pH = pKa × log([A⁻]/[HA])
Rationale: The Henderson-Hasselbalch equation is pH = pKa + log([A⁻]/[HA]), where [A⁻] is the
concentration of the conjugate base and [HA] is the concentration of the weak acid.
5. At a pH equal to the pKa of a weak acid:
A. The acid is completely protonated
B. The acid is completely deprotonated
C. [HA] = [A⁻]
D. pH = 7
Rationale: When pH = pKa, the concentrations of the weak acid (HA) and its conjugate base (A⁻)
are equal. This is the point of maximum buffering capacity.
6. Which of the following is a biological buffer system?
A. HCl/NaOH
B. H₂CO₃/HCO₃⁻
C. NaCl/H₂O
D. Glucose/fructose
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Rationale: The carbonic acid-bicarbonate buffer system (H₂CO₃/HCO₃⁻) is a major biological
buffer that helps maintain blood pH within a narrow range.
7. What is the pH of pure water at 25°C?
A. 0
B. 7
C. 14
D. 1
Rationale: Pure water has a pH of 7 at 25°C, which is considered neutral because [H⁺] = [OH⁻] =
1 × 10⁻⁷ M.
8. The pKa of acetic acid is 4.76. What is the pH of a buffer containing 0.1 M acetic acid and
0.1 M sodium acetate?
A. 4.76
B. 7.00
C. 5.76
D. 3.76
Rationale: Using the Henderson-Hasselbalch equation: pH = pKa + log([A⁻]/[HA]) = 4.76 +
log(0.1/0.1) = 4.76 + 0 = 4.76.
9. Which of the following statements about water is TRUE?
A. Water is a nonpolar molecule
B. Water has a low boiling point compared to other molecules of similar size
C. Water has a high specific heat capacity
D. Water cannot form hydrogen bonds
Rationale: Water has a high specific heat capacity (4.18 J/g·°C), which allows it to absorb
significant heat with minimal temperature change, helping to regulate body temperature.
10. A buffer is most effective when:
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A. pH is far from pKa
B. pH = pKa
C. pH is 2 units above pKa
D. pH is 2 units below pKa
Rationale: A buffer is most effective when the pH is within ±1 pH unit of the pKa, with maximum
buffering capacity at pH = pKa.
11. What is the conjugate base of H₂PO₄⁻?
A. H₃PO₄
B. HPO₄²⁻
C. PO₄³⁻
D. H₂O
Rationale: The conjugate base is formed by removing a proton (H⁺) from the acid. H₂PO₄⁻ →
HPO₄²⁻ + H⁺, so HPO₄²⁻ is the conjugate base.
12. The pH of a solution with [OH⁻] = 1 × 10⁻⁵ M is:
A. 5
B. 9
C. 14
D. 1
Rationale: pOH = −log(10⁻⁵) = 5. pH = 14 − pOH = 14 − 5 = 9.
13. Which of the following is NOT a property of water?
A. High surface tension
B. High dielectric constant
C. Low heat of vaporization
D. High specific heat
Rationale: Water has a high heat of vaporization (40.7 kJ/mol), not a low one, which is
important for sweating and evaporative cooling.
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CHEM 210 BIOCHEMISTRY EXAM WITH VERIFIED
ANSWERS DETAILED RATIONALES GRADED A+
CHEM 210 Biochemistry — Module 1 to 8 Exams
SECTION 1: WATER, pH & BUFFERS (Questions 1–30)
1. Which property of water allows it to dissolve ionic compounds?
A. Low dielectric constant
B. High dielectric constant and ability to form hydrogen bonds
C. Low specific heat
D. Nonpolar nature
Rationale: Water has a high dielectric constant, which reduces the electrostatic attraction
between ions, and it forms hydrogen bonds with ions, stabilizing them in solution. This makes
water an excellent solvent for ionic compounds.
2. The pH of a solution with [H⁺] = 1 × 10⁻⁴ M is:
A. 4
B. 10
C. 1
D. 14
Rationale: pH = −log[H⁺] = −log(1 × 10⁻⁴) = 4. The pH scale is logarithmic and inversely related to
hydrogen ion concentration.
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3. What is the pH of a 0.01 M solution of HCl?
A. 1
B. 2
C. 12
D. 0.01
Rationale: HCl is a strong acid that completely dissociates. [H⁺] = 0.01 M = 1 × 10⁻² M. pH =
−log(10⁻²) = 2.
4. The Henderson-Hasselbalch equation is:
A. pH = pKa + log([A⁻]/[HA])
B. pH = pKa − log([A⁻]/[HA])
C. pH = pKa + log([HA]/[A⁻])
D. pH = pKa × log([A⁻]/[HA])
Rationale: The Henderson-Hasselbalch equation is pH = pKa + log([A⁻]/[HA]), where [A⁻] is the
concentration of the conjugate base and [HA] is the concentration of the weak acid.
5. At a pH equal to the pKa of a weak acid:
A. The acid is completely protonated
B. The acid is completely deprotonated
C. [HA] = [A⁻]
D. pH = 7
Rationale: When pH = pKa, the concentrations of the weak acid (HA) and its conjugate base (A⁻)
are equal. This is the point of maximum buffering capacity.
6. Which of the following is a biological buffer system?
A. HCl/NaOH
B. H₂CO₃/HCO₃⁻
C. NaCl/H₂O
D. Glucose/fructose
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Rationale: The carbonic acid-bicarbonate buffer system (H₂CO₃/HCO₃⁻) is a major biological
buffer that helps maintain blood pH within a narrow range.
7. What is the pH of pure water at 25°C?
A. 0
B. 7
C. 14
D. 1
Rationale: Pure water has a pH of 7 at 25°C, which is considered neutral because [H⁺] = [OH⁻] =
1 × 10⁻⁷ M.
8. The pKa of acetic acid is 4.76. What is the pH of a buffer containing 0.1 M acetic acid and
0.1 M sodium acetate?
A. 4.76
B. 7.00
C. 5.76
D. 3.76
Rationale: Using the Henderson-Hasselbalch equation: pH = pKa + log([A⁻]/[HA]) = 4.76 +
log(0.1/0.1) = 4.76 + 0 = 4.76.
9. Which of the following statements about water is TRUE?
A. Water is a nonpolar molecule
B. Water has a low boiling point compared to other molecules of similar size
C. Water has a high specific heat capacity
D. Water cannot form hydrogen bonds
Rationale: Water has a high specific heat capacity (4.18 J/g·°C), which allows it to absorb
significant heat with minimal temperature change, helping to regulate body temperature.
10. A buffer is most effective when:
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A. pH is far from pKa
B. pH = pKa
C. pH is 2 units above pKa
D. pH is 2 units below pKa
Rationale: A buffer is most effective when the pH is within ±1 pH unit of the pKa, with maximum
buffering capacity at pH = pKa.
11. What is the conjugate base of H₂PO₄⁻?
A. H₃PO₄
B. HPO₄²⁻
C. PO₄³⁻
D. H₂O
Rationale: The conjugate base is formed by removing a proton (H⁺) from the acid. H₂PO₄⁻ →
HPO₄²⁻ + H⁺, so HPO₄²⁻ is the conjugate base.
12. The pH of a solution with [OH⁻] = 1 × 10⁻⁵ M is:
A. 5
B. 9
C. 14
D. 1
Rationale: pOH = −log(10⁻⁵) = 5. pH = 14 − pOH = 14 − 5 = 9.
13. Which of the following is NOT a property of water?
A. High surface tension
B. High dielectric constant
C. Low heat of vaporization
D. High specific heat
Rationale: Water has a high heat of vaporization (40.7 kJ/mol), not a low one, which is
important for sweating and evaporative cooling.
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