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CHEM 210 BIOCHEMISTRY MODULE 1 EXAM ACTUAL
2026/2027 | Water, pH, Buffers, Amino Acids & Protein
Structure | Portage Learning | Complete Questions &
Verified Answers | Pass Guaranteed - A+ Graded
Section 1: Water, pH & Buffers (Q1-15)
Q1. Which property of water is primarily responsible for the ability of plants to
transport water from roots to leaves through xylem vessels?
A. High specific heat B. Cohesion and adhesion C. High heat of vaporization D. Low
density as a solid
B. Cohesion and adhesion [CORRECT]
Rationale: Cohesion (hydrogen bonding between water molecules) and adhesion
(hydrogen bonding between water and xylem walls) together enable capillary action
and transpiration pull; high specific heat (A) stabilizes temperature, high heat of
vaporization (C) drives cooling, and low density as ice (D) insulates aquatic life but
does not drive xylem transport.
"Correct Answer: B"
Q2. At 25°C, if the hydroxide ion concentration [OH⁻] in a solution is 1 × 10⁻⁹ M, what
is the hydrogen ion concentration [H⁺]?
A. 1 × 10⁻⁵ M B. 1 × 10⁻⁹ M C. 1 × 10⁻¹⁴ M D. 1 × 10⁻²³ M
A. 1 × 10⁻⁵ M [CORRECT]
Rationale: Using Kw = [H⁺][OH⁻] = 1 × 10⁻¹⁴ at 25°C, [H⁺] = (1 × 10⁻¹⁴)/(1 × 10⁻⁹) = 1
× 10⁻⁵ M; option B confuses [H⁺] with [OH⁻], C states Kw itself, and D incorrectly adds
exponents.
"Correct Answer: A"
Q3. A patient has a blood pH of 7.20. What is the approximate hydrogen ion
concentration?
A. 6.3 × 10⁻⁷ M B. 6.3 × 10⁻⁸ M C. 1.6 × 10⁻⁷ M D. 1.6 × 10⁻⁸ M
B. 6.3 × 10⁻⁸ M [CORRECT]
,2
Rationale: [H⁺] = 10⁻ᵖᴴ = 10⁻⁷·²⁰ ≈ 6.31 × 10⁻⁸ M; because pH 7.20 is more acidic than
7.40, [H⁺] must be higher than 4.0 × 10⁻⁸ M, and option A incorrectly calculates 10⁻⁷·²
as 6.3 × 10⁻⁷.
"Correct Answer: B"
Q4. In a biochemistry experiment, Solution X completely dissociates in water and has
a pH of 2.0, while Solution Y partially dissociates and has a pH of 2.0. Which
statement accurately compares the two solutions?
A. Solution X has a higher concentration of undissociated acid than Solution Y. B.
Solution Y has a higher total acid concentration than Solution X. C. Solution X is a
strong acid, while Solution Y is a weak acid. D. Both solutions have identical buffer
capacities because their pH values are equal.
C. Solution X is a strong acid, while Solution Y is a weak acid [CORRECT]
Rationale: Complete dissociation characterizes a strong acid (X), whereas partial
dissociation characterizes a weak acid (Y); at identical pH, the weak acid must be
present at higher total concentration, making A and B reversed, and D is incorrect
because neither is necessarily a buffer.
"Correct Answer: C"
Q5. The pKa of a weak acid is defined biochemically as:
A. The pH at which the acid is fully ionized B. The pH at which [HA] = [A⁻] C. The pH
at which buffer capacity is zero D. The pH equal to the acid's molecular weight
B. The pH at which [HA] = [A⁻] [CORRECT]
Rationale: pKa is the pH where the protonated form [HA] equals the deprotonated
form [A⁻]; A describes complete titration, C is false because buffer capacity is maximal
(not zero) at pKa, and D confuses pKa with an unrelated physical property.
"Correct Answer: B"
Q6. A buffer contains 0.10 M acetic acid (pKa = 4.76) and 0.20 M sodium acetate.
What is the pH of this buffer?
A. 4.46 B. 4.76 C. 5.06 D. 5.26
C. 5.06 [CORRECT]
, 3
Rationale: Using the Henderson-Hasselbalch equation: pH = 4.76 + log(0.20/0.10) =
4.76 + log(2) = 4.76 + 0.30 = 5.06; A incorrectly subtracts log(2), B ignores the ratio,
and D uses an incorrect logarithm value.
"Correct Answer: C"
Q7. You need to prepare a phosphate buffer at pH 7.20 using H₂PO₄⁻/HPO₄²⁻ (pKa₂ =
7.20). What ratio of [HPO₄²⁻] to [H₂PO₄⁻] is required?
A. 1:10 B. 1:1 C. 10:1 D. 100:1
B. 1:1 [CORRECT]
Rationale: When pH = pKa, the Henderson-Hasselbalch equation yields log([A⁻]/[HA])
= 0, so [A⁻]/[HA] = 1; A and C represent pH values one unit below or above the pKa,
and D represents a two-unit difference.
"Correct Answer: B"
Q8. A buffer originally at pH 6.0 contains equal concentrations of HA and A⁻ (pKa =
6.0). After adding a small amount of HCl, the concentration of HA becomes 0.30 M
and A⁻ becomes 0.10 M. What is the new pH?
A. 5.22 B. 5.52 C. 6.48 D. 6.78
B. 5.52 [CORRECT]
Rationale: pH = 6.0 + log(0.10/0.30) = 6.0 + log(0.333) = 6.0 − 0.48 = 5.52; A
miscalculates the log value, C adds instead of subtracting, and D incorrectly inverts
the ratio and adds.
"Correct Answer: B"
Q9. What is the pH of a buffer prepared by mixing 0.30 M acetic acid and 0.10 M
sodium acetate? (pKa of acetic acid = 4.76)
A. 4.28 B. 4.76 C. 5.24 D. 5.76
A. 4.28 [CORRECT]
Rationale: pH = 4.76 + log(0.10/0.30) = 4.76 + log(0.333) = 4.76 − 0.48 = 4.28; B
ignores the ratio, C adds 0.48 instead of subtracting, and D uses an incorrect log
value.
"Correct Answer: A"
CHEM 210 BIOCHEMISTRY MODULE 1 EXAM ACTUAL
2026/2027 | Water, pH, Buffers, Amino Acids & Protein
Structure | Portage Learning | Complete Questions &
Verified Answers | Pass Guaranteed - A+ Graded
Section 1: Water, pH & Buffers (Q1-15)
Q1. Which property of water is primarily responsible for the ability of plants to
transport water from roots to leaves through xylem vessels?
A. High specific heat B. Cohesion and adhesion C. High heat of vaporization D. Low
density as a solid
B. Cohesion and adhesion [CORRECT]
Rationale: Cohesion (hydrogen bonding between water molecules) and adhesion
(hydrogen bonding between water and xylem walls) together enable capillary action
and transpiration pull; high specific heat (A) stabilizes temperature, high heat of
vaporization (C) drives cooling, and low density as ice (D) insulates aquatic life but
does not drive xylem transport.
"Correct Answer: B"
Q2. At 25°C, if the hydroxide ion concentration [OH⁻] in a solution is 1 × 10⁻⁹ M, what
is the hydrogen ion concentration [H⁺]?
A. 1 × 10⁻⁵ M B. 1 × 10⁻⁹ M C. 1 × 10⁻¹⁴ M D. 1 × 10⁻²³ M
A. 1 × 10⁻⁵ M [CORRECT]
Rationale: Using Kw = [H⁺][OH⁻] = 1 × 10⁻¹⁴ at 25°C, [H⁺] = (1 × 10⁻¹⁴)/(1 × 10⁻⁹) = 1
× 10⁻⁵ M; option B confuses [H⁺] with [OH⁻], C states Kw itself, and D incorrectly adds
exponents.
"Correct Answer: A"
Q3. A patient has a blood pH of 7.20. What is the approximate hydrogen ion
concentration?
A. 6.3 × 10⁻⁷ M B. 6.3 × 10⁻⁸ M C. 1.6 × 10⁻⁷ M D. 1.6 × 10⁻⁸ M
B. 6.3 × 10⁻⁸ M [CORRECT]
,2
Rationale: [H⁺] = 10⁻ᵖᴴ = 10⁻⁷·²⁰ ≈ 6.31 × 10⁻⁸ M; because pH 7.20 is more acidic than
7.40, [H⁺] must be higher than 4.0 × 10⁻⁸ M, and option A incorrectly calculates 10⁻⁷·²
as 6.3 × 10⁻⁷.
"Correct Answer: B"
Q4. In a biochemistry experiment, Solution X completely dissociates in water and has
a pH of 2.0, while Solution Y partially dissociates and has a pH of 2.0. Which
statement accurately compares the two solutions?
A. Solution X has a higher concentration of undissociated acid than Solution Y. B.
Solution Y has a higher total acid concentration than Solution X. C. Solution X is a
strong acid, while Solution Y is a weak acid. D. Both solutions have identical buffer
capacities because their pH values are equal.
C. Solution X is a strong acid, while Solution Y is a weak acid [CORRECT]
Rationale: Complete dissociation characterizes a strong acid (X), whereas partial
dissociation characterizes a weak acid (Y); at identical pH, the weak acid must be
present at higher total concentration, making A and B reversed, and D is incorrect
because neither is necessarily a buffer.
"Correct Answer: C"
Q5. The pKa of a weak acid is defined biochemically as:
A. The pH at which the acid is fully ionized B. The pH at which [HA] = [A⁻] C. The pH
at which buffer capacity is zero D. The pH equal to the acid's molecular weight
B. The pH at which [HA] = [A⁻] [CORRECT]
Rationale: pKa is the pH where the protonated form [HA] equals the deprotonated
form [A⁻]; A describes complete titration, C is false because buffer capacity is maximal
(not zero) at pKa, and D confuses pKa with an unrelated physical property.
"Correct Answer: B"
Q6. A buffer contains 0.10 M acetic acid (pKa = 4.76) and 0.20 M sodium acetate.
What is the pH of this buffer?
A. 4.46 B. 4.76 C. 5.06 D. 5.26
C. 5.06 [CORRECT]
, 3
Rationale: Using the Henderson-Hasselbalch equation: pH = 4.76 + log(0.20/0.10) =
4.76 + log(2) = 4.76 + 0.30 = 5.06; A incorrectly subtracts log(2), B ignores the ratio,
and D uses an incorrect logarithm value.
"Correct Answer: C"
Q7. You need to prepare a phosphate buffer at pH 7.20 using H₂PO₄⁻/HPO₄²⁻ (pKa₂ =
7.20). What ratio of [HPO₄²⁻] to [H₂PO₄⁻] is required?
A. 1:10 B. 1:1 C. 10:1 D. 100:1
B. 1:1 [CORRECT]
Rationale: When pH = pKa, the Henderson-Hasselbalch equation yields log([A⁻]/[HA])
= 0, so [A⁻]/[HA] = 1; A and C represent pH values one unit below or above the pKa,
and D represents a two-unit difference.
"Correct Answer: B"
Q8. A buffer originally at pH 6.0 contains equal concentrations of HA and A⁻ (pKa =
6.0). After adding a small amount of HCl, the concentration of HA becomes 0.30 M
and A⁻ becomes 0.10 M. What is the new pH?
A. 5.22 B. 5.52 C. 6.48 D. 6.78
B. 5.52 [CORRECT]
Rationale: pH = 6.0 + log(0.10/0.30) = 6.0 + log(0.333) = 6.0 − 0.48 = 5.52; A
miscalculates the log value, C adds instead of subtracting, and D incorrectly inverts
the ratio and adds.
"Correct Answer: B"
Q9. What is the pH of a buffer prepared by mixing 0.30 M acetic acid and 0.10 M
sodium acetate? (pKa of acetic acid = 4.76)
A. 4.28 B. 4.76 C. 5.24 D. 5.76
A. 4.28 [CORRECT]
Rationale: pH = 4.76 + log(0.10/0.30) = 4.76 + log(0.333) = 4.76 − 0.48 = 4.28; B
ignores the ratio, C adds 0.48 instead of subtracting, and D uses an incorrect log
value.
"Correct Answer: A"
