CHEM134 Practice Exam 9 Acids and
Bases Practice Exam Questions And
Correct Answers (Verified Answers)
Plus Rationales 2026 Q&A | Instant
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1. Which statement best describes an Arrhenius acid?
A. A substance that produces OH− ions when dissolved in water
B. A substance that accepts a proton
C. A substance that donates an electron pair
D. A substance that produces H+ ions in aqueous solution
Answer: D
Rationale: An Arrhenius acid is defined as a substance that increases
the concentration of H+ in aqueous solution. In modern aqueous
chemistry, the H+ is actually associated with water as H3O+, but the
simplified H+ notation is commonly used. An Arrhenius base, in
contrast, increases OH− concentration. This definition is limited
primarily to aqueous solutions, whereas Brønsted–Lowry and Lewis
definitions are broader.
2. According to the Brønsted–Lowry definition, an acid is a substance
that:
A. Donates a proton
B. Accepts an electron pair
C. Produces hydroxide ions
D. Releases electrons
,Answer: A
Rationale: Brønsted–Lowry acid–base theory defines an acid as a
proton donor and a base as a proton acceptor. This definition is
broader than the Arrhenius definition because it does not require the
substance to produce H+ directly in water. For example, NH4+ can
donate a proton to water, making NH4+ a Brønsted–Lowry acid.
3. Which species acts as a Brønsted–Lowry base?
A. HCl
B. H3O+
C. NH3
D. HNO3
Answer: C
Rationale: NH3 acts as a Brønsted–Lowry base because it can accept a
proton. When ammonia reacts with water, NH3 accepts H+ from H2O
to form NH4+. HCl, HNO3, and H3O+ are proton donors under
appropriate conditions and therefore act as acids rather than bases in
this context.
4. Which species is amphiprotic?
A. HCl
B. HCO3−
C. Na+
D. Cl−
Answer: B
Rationale: An amphiprotic species can both donate and accept a
proton. Bicarbonate, HCO3−, can donate H+ to form CO3^2− and
can accept H+ to form H2CO3. Water is another important
,amphiprotic substance because it can form either H3O+ or OH−
depending on the reaction partner.
5. What is the conjugate base of H2CO3?
A. H3CO3+
B. CO3^2−
C. OH−
D. HCO3−
Answer: D
Rationale: A conjugate base forms when an acid loses one proton.
H2CO3 loses one H+ to produce HCO3−. The acid and conjugate base
differ by exactly one proton. Therefore, H2CO3/HCO3− is a conjugate
acid–base pair.
6. What is the conjugate acid of NH3?
A. NH4+
B. NH2−
C. N2H4
D. HNO3
Answer: A
Rationale: The conjugate acid of a base is formed when the base
accepts one proton. NH3 accepts H+ to become NH4+. Thus, NH3 and
NH4+ form a conjugate acid–base pair. The charge increases by one
unit when the neutral ammonia molecule accepts a positively charged
proton.
7. Which equation represents the ionization of a strong acid HA in
water?
, A. HA + OH− ⇌ A− + H2O
B. HA ⇌ H+ + A−
C. HA + H2O → H3O+ + A−
D. HA + H2O ⇌ HA2+ + OH−
Answer: C
Rationale: In water, an acid transfers its proton to a water molecule,
producing hydronium and the conjugate base. A strong acid ionizes
essentially completely, so a one-way arrow is appropriate for an
introductory representation. The equation HA + H2O → H3O+ + A−
demonstrates both proton transfer and the role of water as a base.
8. Which acid is classified as a strong acid?
A. HF
B. CH3COOH
C. H2CO3
D. HCl
Answer: D
Rationale: Hydrochloric acid, HCl, is one of the commonly recognized
strong acids. Strong acids ionize essentially completely in water. HF,
acetic acid, and carbonic acid are weak acids because they establish
equilibria between their molecular and ionized forms. Strong-acid
classification refers to extent of ionization, not simply concentration.
9. Which of the following is a weak acid?
A. CH3COOH
B. HCl
C. HNO3
D. HClO4
Answer: A
Bases Practice Exam Questions And
Correct Answers (Verified Answers)
Plus Rationales 2026 Q&A | Instant
Download Pdf
1. Which statement best describes an Arrhenius acid?
A. A substance that produces OH− ions when dissolved in water
B. A substance that accepts a proton
C. A substance that donates an electron pair
D. A substance that produces H+ ions in aqueous solution
Answer: D
Rationale: An Arrhenius acid is defined as a substance that increases
the concentration of H+ in aqueous solution. In modern aqueous
chemistry, the H+ is actually associated with water as H3O+, but the
simplified H+ notation is commonly used. An Arrhenius base, in
contrast, increases OH− concentration. This definition is limited
primarily to aqueous solutions, whereas Brønsted–Lowry and Lewis
definitions are broader.
2. According to the Brønsted–Lowry definition, an acid is a substance
that:
A. Donates a proton
B. Accepts an electron pair
C. Produces hydroxide ions
D. Releases electrons
,Answer: A
Rationale: Brønsted–Lowry acid–base theory defines an acid as a
proton donor and a base as a proton acceptor. This definition is
broader than the Arrhenius definition because it does not require the
substance to produce H+ directly in water. For example, NH4+ can
donate a proton to water, making NH4+ a Brønsted–Lowry acid.
3. Which species acts as a Brønsted–Lowry base?
A. HCl
B. H3O+
C. NH3
D. HNO3
Answer: C
Rationale: NH3 acts as a Brønsted–Lowry base because it can accept a
proton. When ammonia reacts with water, NH3 accepts H+ from H2O
to form NH4+. HCl, HNO3, and H3O+ are proton donors under
appropriate conditions and therefore act as acids rather than bases in
this context.
4. Which species is amphiprotic?
A. HCl
B. HCO3−
C. Na+
D. Cl−
Answer: B
Rationale: An amphiprotic species can both donate and accept a
proton. Bicarbonate, HCO3−, can donate H+ to form CO3^2− and
can accept H+ to form H2CO3. Water is another important
,amphiprotic substance because it can form either H3O+ or OH−
depending on the reaction partner.
5. What is the conjugate base of H2CO3?
A. H3CO3+
B. CO3^2−
C. OH−
D. HCO3−
Answer: D
Rationale: A conjugate base forms when an acid loses one proton.
H2CO3 loses one H+ to produce HCO3−. The acid and conjugate base
differ by exactly one proton. Therefore, H2CO3/HCO3− is a conjugate
acid–base pair.
6. What is the conjugate acid of NH3?
A. NH4+
B. NH2−
C. N2H4
D. HNO3
Answer: A
Rationale: The conjugate acid of a base is formed when the base
accepts one proton. NH3 accepts H+ to become NH4+. Thus, NH3 and
NH4+ form a conjugate acid–base pair. The charge increases by one
unit when the neutral ammonia molecule accepts a positively charged
proton.
7. Which equation represents the ionization of a strong acid HA in
water?
, A. HA + OH− ⇌ A− + H2O
B. HA ⇌ H+ + A−
C. HA + H2O → H3O+ + A−
D. HA + H2O ⇌ HA2+ + OH−
Answer: C
Rationale: In water, an acid transfers its proton to a water molecule,
producing hydronium and the conjugate base. A strong acid ionizes
essentially completely, so a one-way arrow is appropriate for an
introductory representation. The equation HA + H2O → H3O+ + A−
demonstrates both proton transfer and the role of water as a base.
8. Which acid is classified as a strong acid?
A. HF
B. CH3COOH
C. H2CO3
D. HCl
Answer: D
Rationale: Hydrochloric acid, HCl, is one of the commonly recognized
strong acids. Strong acids ionize essentially completely in water. HF,
acetic acid, and carbonic acid are weak acids because they establish
equilibria between their molecular and ionized forms. Strong-acid
classification refers to extent of ionization, not simply concentration.
9. Which of the following is a weak acid?
A. CH3COOH
B. HCl
C. HNO3
D. HClO4
Answer: A
