BioChem 210 Final Exam – Portage
Learning QUESTIONS AND ANSWERS
WITH RATIONALES/ GRADED
A+/2026\2027 UPDATE /100%CORRECT
.
Section 1: Water, pH, and Buffers (Questions 1–15)
1. The pH of a solution is 4.5. What is the [H⁺]?
A) 4.5 M
B) 3.16 × 10⁻⁵ M
C) 2.0 × 10⁻⁴ M
D) 5.0 × 10⁻⁴ M
2. Which buffer system is most important in human blood?
A) Phosphate buffer
B) Bicarbonate buffer
C) Tris buffer
D) Acetate buffer
3. True/False: A solution with a pOH of 8 is acidic.
4. The pKa of acetic acid is 4.76. At pH 5.76, the ratio of [A⁻]/[HA] is:
A) 0.1
B) 1
C) 10
D) 100
5. Which statement about water is false?
A) Water has a high specific heat.
B) Water has a low dielectric constant.
C) Water molecules form hydrogen bonds.
D) Water is a good solvent for polar molecules.
6–10: Matching – Match the term to its definition.
6. Amphipathic
, 7. Hydrophobic effect
8. pKa
9. Henderson-Hasselbalch equation
10. Ion product of water (Kw)
Definitions:
A) pH = pKa + log([A⁻]/[HA])
B) 1 × 10⁻¹⁴ at 25°C
C) Molecules with both polar and nonpolar regions
D) Nonpolar molecules clustering together in water
E) pH at which a weak acid is 50% ionized
11. At pH 7.4, the bicarbonate buffer system (pKa = 6.1) is:
A) Maximally effective
B) More effective for acids than bases
C) More effective for bases than acids
D) Equally effective for acids and bases
12–15: Fill in the blank.
12. A solution that resists pH change upon addition of small amounts of acid or base is a __________.
13. The Kw at 37°C is about 2.5 × 10⁻¹⁴, so pKw = __________ (calculate).
14. Adding 0.01 mol of NaOH to 1 L of pure water changes the pH from 7 to __________.
15. The conjugate base of H₂PO₄⁻ is __________.
Section 1 Answers & Rationales
1. B – [H⁺] = 10⁻⁴·⁵ = 3.16 × 10⁻⁵ M.
2. B – Bicarbonate (H₂CO₃/HCO₃⁻) is the main blood buffer.
3. False – pOH 8 → pH 6 (acidic? Wait: pH + pOH = 14 → pH = 6, acidic, so statement “pOH 8 is
acidic” is false because pOH refers to basicity. Actually pH 6 is acidic, but the statement says
“pOH of 8 is acidic” – that’s false; pOH 8 means pH 6, acidic, so the statement is true? Let’s
check: If pOH=8, pH=6 → acidic. The statement “pOH of 8 is acidic” is ambiguous but generally
means “a solution with pOH 8 is acidic” – true. But careful: Many students get confused. Correct
answer: True (because pH 6 is acidic). I’ll clarify in rationale. Rationale: pOH 8 → pH 6 (<7) →
acidic.
4. C – log([A⁻]/[HA]) = pH – pKa = 1 → ratio = 10.
5. B – Water has a high dielectric constant (~80), not low.
6–10: 6-C, 7-D, 8-E, 9-A, 10-B.
6. C – Since pH > pKa, the buffer is better for bases (more A⁻ available to neutralize H⁺ from added
base? Wait: pH > pKa means more A⁻; A⁻ neutralizes added acid, not base. Actually: For bases,
HA neutralizes OH⁻. If pH > pKa, [A⁻] > [HA], so weak in HA → less ability to neutralize base. So
it’s better for acids. Let’s correct: At pH 7.4 > 6.1, [HCO₃⁻] > [H₂CO₃]. HCO₃⁻ neutralizes added
Learning QUESTIONS AND ANSWERS
WITH RATIONALES/ GRADED
A+/2026\2027 UPDATE /100%CORRECT
.
Section 1: Water, pH, and Buffers (Questions 1–15)
1. The pH of a solution is 4.5. What is the [H⁺]?
A) 4.5 M
B) 3.16 × 10⁻⁵ M
C) 2.0 × 10⁻⁴ M
D) 5.0 × 10⁻⁴ M
2. Which buffer system is most important in human blood?
A) Phosphate buffer
B) Bicarbonate buffer
C) Tris buffer
D) Acetate buffer
3. True/False: A solution with a pOH of 8 is acidic.
4. The pKa of acetic acid is 4.76. At pH 5.76, the ratio of [A⁻]/[HA] is:
A) 0.1
B) 1
C) 10
D) 100
5. Which statement about water is false?
A) Water has a high specific heat.
B) Water has a low dielectric constant.
C) Water molecules form hydrogen bonds.
D) Water is a good solvent for polar molecules.
6–10: Matching – Match the term to its definition.
6. Amphipathic
, 7. Hydrophobic effect
8. pKa
9. Henderson-Hasselbalch equation
10. Ion product of water (Kw)
Definitions:
A) pH = pKa + log([A⁻]/[HA])
B) 1 × 10⁻¹⁴ at 25°C
C) Molecules with both polar and nonpolar regions
D) Nonpolar molecules clustering together in water
E) pH at which a weak acid is 50% ionized
11. At pH 7.4, the bicarbonate buffer system (pKa = 6.1) is:
A) Maximally effective
B) More effective for acids than bases
C) More effective for bases than acids
D) Equally effective for acids and bases
12–15: Fill in the blank.
12. A solution that resists pH change upon addition of small amounts of acid or base is a __________.
13. The Kw at 37°C is about 2.5 × 10⁻¹⁴, so pKw = __________ (calculate).
14. Adding 0.01 mol of NaOH to 1 L of pure water changes the pH from 7 to __________.
15. The conjugate base of H₂PO₄⁻ is __________.
Section 1 Answers & Rationales
1. B – [H⁺] = 10⁻⁴·⁵ = 3.16 × 10⁻⁵ M.
2. B – Bicarbonate (H₂CO₃/HCO₃⁻) is the main blood buffer.
3. False – pOH 8 → pH 6 (acidic? Wait: pH + pOH = 14 → pH = 6, acidic, so statement “pOH 8 is
acidic” is false because pOH refers to basicity. Actually pH 6 is acidic, but the statement says
“pOH of 8 is acidic” – that’s false; pOH 8 means pH 6, acidic, so the statement is true? Let’s
check: If pOH=8, pH=6 → acidic. The statement “pOH of 8 is acidic” is ambiguous but generally
means “a solution with pOH 8 is acidic” – true. But careful: Many students get confused. Correct
answer: True (because pH 6 is acidic). I’ll clarify in rationale. Rationale: pOH 8 → pH 6 (<7) →
acidic.
4. C – log([A⁻]/[HA]) = pH – pKa = 1 → ratio = 10.
5. B – Water has a high dielectric constant (~80), not low.
6–10: 6-C, 7-D, 8-E, 9-A, 10-B.
6. C – Since pH > pKa, the buffer is better for bases (more A⁻ available to neutralize H⁺ from added
base? Wait: pH > pKa means more A⁻; A⁻ neutralizes added acid, not base. Actually: For bases,
HA neutralizes OH⁻. If pH > pKa, [A⁻] > [HA], so weak in HA → less ability to neutralize base. So
it’s better for acids. Let’s correct: At pH 7.4 > 6.1, [HCO₃⁻] > [H₂CO₃]. HCO₃⁻ neutralizes added
