CHEM 210 BIOCHEMISTRY MODULE 2
EXAM MASTERY: VERIFIED QUESTIONS
& DETAILED RATIONALES COVERING
ACID-BASE CHEMISTRY, WATER
PROPERTIES, NON-COVALENT FORCES,
BUFFERS, THERMODYNAMICS, AND
PROTEIN STRUCTURE – PORTAGE
LEARNING
Acid-Base Chemistry and pH Calculations
1. The pH of a solution of 0.0010 M NaOH is:
A. 3.0
B. 8.0
C. 11.0
D. 14.0
E. 1.0 x 10⁻¹¹
Answer: C. 11.0
Rationale: For strong bases like NaOH, [OH⁻] = 0.0010 M. Using Kw =
[H⁺][OH⁻] = 1.0 x 10⁻¹⁴, [H⁺] = 1.0 x 10⁻¹¹, so pH = -log(1.0 x 10⁻¹¹) = 11.0 .
,2. The H⁺ concentration of a solution is 1.2 x 10⁻³ M. What is the pH?
A. 1.20
B. -1.20
C. 2.92
D. -2.92
E. 3.12
Answer: C. 2.92
Rationale: pH = -log[H⁺] = -log(1.2 x 10⁻³) = 2.92 .
3. If the Ka of an acid is 5.63 x 10⁻³, what is the pKa?
A. 6.86
B. 2.25
C. 5.63
D. 10.12
E. 1.38
Answer: B. 2.25
Rationale: pKa = -log(Ka) = -log(5.63 x 10⁻³) = 2.25 .
4. List the acids in DECREASING order of strength (strongest to
weakest):
Nitrous acid (Ka = 4.0 x 10⁻⁴)
Acetic acid (Ka = 1.7 x 10⁻⁵)
Phosphoric acid (Ka = 7.3 x 10⁻³)
,A. Nitrous acid, acetic acid, phosphoric acid
B. Acetic acid, nitrous acid, phosphoric acid
C. Phosphoric acid, nitrous acid, acetic acid
D. Acetic acid, phosphoric acid, nitrous acid
Answer: C. Phosphoric acid, nitrous acid, acetic acid
Rationale: A larger Ka value indicates a stronger acid. Ka values:
phosphoric acid (7.3 x 10⁻³) > nitrous acid (4.0 x 10⁻⁴) > acetic acid (1.7 x
10⁻⁵). Therefore, decreasing strength: phosphoric acid > nitrous acid >
acetic acid .
5. List the acids in INCREASING order of strength (weakest to
strongest):
A. Nitrous acid, acetic acid, phosphoric acid
B. Acetic acid, nitrous acid, phosphoric acid
C. Phosphoric acid, nitrous acid, acetic acid
D. Acetic acid, phosphoric acid, nitrous acid
Answer: B. Acetic acid, nitrous acid, phosphoric acid
Rationale: Smaller Ka means weaker acid. Acetic acid (1.7 x 10⁻⁵) < nitrous
acid (4.0 x 10⁻⁴) < phosphoric acid (7.3 x 10⁻³) .
6. The concentration of a solution with a pH of 5.65 is:
A. 5.65 M
B. 2.24 x 10⁻⁶ M
, C. 1.0 x 10⁻⁵ M
D. 5.6 x 10⁻⁵ M
Answer: B. 2.24 x 10⁻⁶ M
Rationale: [H⁺] = 10⁻pH = 10⁻⁵·⁶⁵ = 2.24 x 10⁻⁶ M .
7. What is the pKa of an acid with a Ka of 2.67 x 10⁻⁵?
A. 5.67
B. 2.67
C. 4.57
D. 3.45
Answer: C. 4.57
Rationale: pKa = -log(2.67 x 10⁻⁵) = 4.57 .
8. Nitrous acid (Ka = 4.0 x 10⁻⁴) compared to acetic acid (Ka = 1.7 x
10⁻⁵). Which is stronger?
A. Acetic acid
B. Nitrous acid
C. They are equal
D. Cannot be determined
Answer: B. Nitrous acid
Rationale: Nitrous acid has a larger Ka (4.0 x 10⁻⁴ > 1.7 x 10⁻⁵), meaning it
dissociates more and is the stronger acid .
EXAM MASTERY: VERIFIED QUESTIONS
& DETAILED RATIONALES COVERING
ACID-BASE CHEMISTRY, WATER
PROPERTIES, NON-COVALENT FORCES,
BUFFERS, THERMODYNAMICS, AND
PROTEIN STRUCTURE – PORTAGE
LEARNING
Acid-Base Chemistry and pH Calculations
1. The pH of a solution of 0.0010 M NaOH is:
A. 3.0
B. 8.0
C. 11.0
D. 14.0
E. 1.0 x 10⁻¹¹
Answer: C. 11.0
Rationale: For strong bases like NaOH, [OH⁻] = 0.0010 M. Using Kw =
[H⁺][OH⁻] = 1.0 x 10⁻¹⁴, [H⁺] = 1.0 x 10⁻¹¹, so pH = -log(1.0 x 10⁻¹¹) = 11.0 .
,2. The H⁺ concentration of a solution is 1.2 x 10⁻³ M. What is the pH?
A. 1.20
B. -1.20
C. 2.92
D. -2.92
E. 3.12
Answer: C. 2.92
Rationale: pH = -log[H⁺] = -log(1.2 x 10⁻³) = 2.92 .
3. If the Ka of an acid is 5.63 x 10⁻³, what is the pKa?
A. 6.86
B. 2.25
C. 5.63
D. 10.12
E. 1.38
Answer: B. 2.25
Rationale: pKa = -log(Ka) = -log(5.63 x 10⁻³) = 2.25 .
4. List the acids in DECREASING order of strength (strongest to
weakest):
Nitrous acid (Ka = 4.0 x 10⁻⁴)
Acetic acid (Ka = 1.7 x 10⁻⁵)
Phosphoric acid (Ka = 7.3 x 10⁻³)
,A. Nitrous acid, acetic acid, phosphoric acid
B. Acetic acid, nitrous acid, phosphoric acid
C. Phosphoric acid, nitrous acid, acetic acid
D. Acetic acid, phosphoric acid, nitrous acid
Answer: C. Phosphoric acid, nitrous acid, acetic acid
Rationale: A larger Ka value indicates a stronger acid. Ka values:
phosphoric acid (7.3 x 10⁻³) > nitrous acid (4.0 x 10⁻⁴) > acetic acid (1.7 x
10⁻⁵). Therefore, decreasing strength: phosphoric acid > nitrous acid >
acetic acid .
5. List the acids in INCREASING order of strength (weakest to
strongest):
A. Nitrous acid, acetic acid, phosphoric acid
B. Acetic acid, nitrous acid, phosphoric acid
C. Phosphoric acid, nitrous acid, acetic acid
D. Acetic acid, phosphoric acid, nitrous acid
Answer: B. Acetic acid, nitrous acid, phosphoric acid
Rationale: Smaller Ka means weaker acid. Acetic acid (1.7 x 10⁻⁵) < nitrous
acid (4.0 x 10⁻⁴) < phosphoric acid (7.3 x 10⁻³) .
6. The concentration of a solution with a pH of 5.65 is:
A. 5.65 M
B. 2.24 x 10⁻⁶ M
, C. 1.0 x 10⁻⁵ M
D. 5.6 x 10⁻⁵ M
Answer: B. 2.24 x 10⁻⁶ M
Rationale: [H⁺] = 10⁻pH = 10⁻⁵·⁶⁵ = 2.24 x 10⁻⁶ M .
7. What is the pKa of an acid with a Ka of 2.67 x 10⁻⁵?
A. 5.67
B. 2.67
C. 4.57
D. 3.45
Answer: C. 4.57
Rationale: pKa = -log(2.67 x 10⁻⁵) = 4.57 .
8. Nitrous acid (Ka = 4.0 x 10⁻⁴) compared to acetic acid (Ka = 1.7 x
10⁻⁵). Which is stronger?
A. Acetic acid
B. Nitrous acid
C. They are equal
D. Cannot be determined
Answer: B. Nitrous acid
Rationale: Nitrous acid has a larger Ka (4.0 x 10⁻⁴ > 1.7 x 10⁻⁵), meaning it
dissociates more and is the stronger acid .
