CHEM 104 Module 4 Exam: Acid-Base Equilibria, Buffers, Titrations,
and Ksp 2026/2027 UPDATE
1. Which of the following is the definition of a Bronsted-Lowry base?
A. A substance that accepts a proton (H+)
B. A substance that produces hydrogen ions in water
C. A substance that donates a pair of electrons
D. A substance that donates a proton (H+)
Answer: A
Rationale: In the Bronsted-Lowry theory, an acid is a proton donor and a base is a proton
acceptor.
2. Identify the conjugate base of HSO4- in a reaction.
A. H2SO4
B. H3O+
C. OH-
D. SO4^2-
Answer: D
Rationale: The conjugate base is formed when an acid loses a proton. Removing H+ from
HSO4- results in SO4^2-.
,3. Which of the following describes a solution with a pH of 4.5?
A. Strongly basic
B. Neutral
C. Weakly basic
D. Acidic
Answer: D
Rationale: Any solution with a pH less than 7.0 at 25 degrees Celsius is considered acidic.
4. What is the hydroxide ion concentration [OH-] of a solution with a pOH of
3.20?
A. 1.58 x 10^-11 M
B. 6.31 x 10^-4 M
C. 3.20 x 10^-3 M
D. 1.00 x 10^-7 M
Answer: B
Rationale: The concentration of OH- is calculated as 10 to the power of negative pOH: 10^-
3.20 = 6.31 x 10^-4 M.
5. In a 0.10 M solution of a weak acid HA, the [H+] is found to be 0.0025 M.
What is the Ka for this acid?
A. 2.5 x 10^-2
B. 6.25 x 10^-5
C. 6.25 x 10^-4
D. 2.5 x 10^-5
Answer: B
Rationale: Ka = [H+][A-] / [HA]. Assuming [H+] = [A-], Ka = (0.0025)^.10 = 6.25 x 10^-
5.
, 6. Which relationship between Ka and Kb for a conjugate acid-base pair is
correct at 25 degrees Celsius?
A. Ka * Kb = 1.0 x 10^-14
B. Ka / Kb = Kw
C. Ka + Kb = 14
D. Ka * Kb = 1.0 x 10^-7
Answer: A
Rationale: The product of the acid dissociation constant (Ka) and its conjugate base
dissociation constant (Kb) equals the autoionization constant of water (Kw), which is 1.0 x
10^-14 at 25C.
7. A solution has a [H3O+] = 2.0 x 10^-9 M. What is the pH of this solution?
A. 9.00
B. 5.30
C. 8.70
D. 2.00
Answer: C
Rationale: pH = -log[H3O+]. -log(2.0 x 10^-9) = 8.698, which rounds to 8.70.
8. Which of the following is a strong base?
A. NH3
B. CH3NH2
C. Al(OH)3
D. KOH
Answer: D
Rationale: KOH is an alkali metal hydroxide, which are all strong bases that dissociate
completely in water.
and Ksp 2026/2027 UPDATE
1. Which of the following is the definition of a Bronsted-Lowry base?
A. A substance that accepts a proton (H+)
B. A substance that produces hydrogen ions in water
C. A substance that donates a pair of electrons
D. A substance that donates a proton (H+)
Answer: A
Rationale: In the Bronsted-Lowry theory, an acid is a proton donor and a base is a proton
acceptor.
2. Identify the conjugate base of HSO4- in a reaction.
A. H2SO4
B. H3O+
C. OH-
D. SO4^2-
Answer: D
Rationale: The conjugate base is formed when an acid loses a proton. Removing H+ from
HSO4- results in SO4^2-.
,3. Which of the following describes a solution with a pH of 4.5?
A. Strongly basic
B. Neutral
C. Weakly basic
D. Acidic
Answer: D
Rationale: Any solution with a pH less than 7.0 at 25 degrees Celsius is considered acidic.
4. What is the hydroxide ion concentration [OH-] of a solution with a pOH of
3.20?
A. 1.58 x 10^-11 M
B. 6.31 x 10^-4 M
C. 3.20 x 10^-3 M
D. 1.00 x 10^-7 M
Answer: B
Rationale: The concentration of OH- is calculated as 10 to the power of negative pOH: 10^-
3.20 = 6.31 x 10^-4 M.
5. In a 0.10 M solution of a weak acid HA, the [H+] is found to be 0.0025 M.
What is the Ka for this acid?
A. 2.5 x 10^-2
B. 6.25 x 10^-5
C. 6.25 x 10^-4
D. 2.5 x 10^-5
Answer: B
Rationale: Ka = [H+][A-] / [HA]. Assuming [H+] = [A-], Ka = (0.0025)^.10 = 6.25 x 10^-
5.
, 6. Which relationship between Ka and Kb for a conjugate acid-base pair is
correct at 25 degrees Celsius?
A. Ka * Kb = 1.0 x 10^-14
B. Ka / Kb = Kw
C. Ka + Kb = 14
D. Ka * Kb = 1.0 x 10^-7
Answer: A
Rationale: The product of the acid dissociation constant (Ka) and its conjugate base
dissociation constant (Kb) equals the autoionization constant of water (Kw), which is 1.0 x
10^-14 at 25C.
7. A solution has a [H3O+] = 2.0 x 10^-9 M. What is the pH of this solution?
A. 9.00
B. 5.30
C. 8.70
D. 2.00
Answer: C
Rationale: pH = -log[H3O+]. -log(2.0 x 10^-9) = 8.698, which rounds to 8.70.
8. Which of the following is a strong base?
A. NH3
B. CH3NH2
C. Al(OH)3
D. KOH
Answer: D
Rationale: KOH is an alkali metal hydroxide, which are all strong bases that dissociate
completely in water.
