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AP Chemistry Practice Quiz: Introduction to Acid-Base Reactions

Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026

Test your understanding with short quizzes. This quiz has 10 questions to check your progress.

Question 1 of 10

According to the Brønsted-Lowry definition, a species that acts as a proton donor in a reaction is best described as which of the following?

All Questions (10)

According to the Brønsted-Lowry definition, a species that acts as a proton donor in a reaction is best described as which of the following?

A) A Brønsted-Lowry base

B) A Brønsted-Lowry acid

C) A conjugate acid

D) A conjugate base

Correct Answer: B

The provided content defines a Brønsted-Lowry acid as a proton donor.

In an acid-base reaction, what is formed when a Brønsted-Lowry base accepts a proton?

A) Its conjugate acid

B) Its conjugate base

C) A salt

D) Water

Correct Answer: A

By definition, a Brønsted-Lowry base accepts a proton. The species formed after accepting the proton is its conjugate acid. For example, when the base NH₃ accepts a proton, it forms its conjugate acid, NH₄⁺.

Consider the following reversible reaction: HF(aq) + H₂O(l) ⇌ F⁻(aq) + H₃O⁺(aq). Which species acts as the Brønsted-Lowry base in the forward reaction?

A) HF

B) H₂O

C) F⁻

D) H₃O⁺

Correct Answer: B

In the forward reaction, the HF molecule donates a proton to the H₂O molecule. Since a Brønsted-Lowry base is a proton acceptor, H₂O is the base.

What is the conjugate base of the Brønsted-Lowry acid HSO₄⁻?

A) H₂SO₄

B) SO₄²⁻

C) H₃O⁺

D) OH⁻

Correct Answer: B

A conjugate base is formed when a Brønsted-Lowry acid donates a proton (H⁺). When HSO₄⁻ donates a proton, it forms the sulfate ion, SO₄²⁻.

What is the conjugate acid of the Brønsted-Lowry base HPO₄²⁻?

A) PO₄³⁻

B) H₂PO₄⁻

C) H₃PO₄

D) H₃O⁺

Correct Answer: B

A conjugate acid is formed when a Brønsted-Lowry base accepts a proton (H⁺). When HPO₄²⁻ accepts a proton, it forms the dihydrogen phosphate ion, H₂PO₄⁻.

In the reaction NH₃(aq) + H₂O(l) ⇌ NH₄⁺(aq) + OH⁻(aq), which of the following represents a conjugate acid-base pair?

A) NH₃ and H₂O

B) NH₄⁺ and OH⁻

C) H₂O and NH₄⁺

D) NH₃ and NH₄⁺

Correct Answer: D

A conjugate acid-base pair consists of two species that differ by a single proton (H⁺). NH₃ acts as a base and accepts a proton to become its conjugate acid, NH₄⁺. Therefore, NH₃ and NH₄⁺ form a conjugate acid-base pair.

When an acid such as HCl ionizes in water, the water molecule plays a specific role. Based on the Brønsted-Lowry theory, how does water function in this aqueous solution?

A) As an acid, by donating a proton.

B) As a base, by accepting a proton.

C) As a spectator ion, remaining unchanged.

D) As a conjugate base, by losing an electron.

Correct Answer: B

The provided content states that water's molecular structure allows it to accept protons from dissolved species. When an acid like HCl is in water, the water molecule accepts a proton (H⁺) from the acid to form H₃O⁺, thus acting as a Brønsted-Lowry base.

For the equilibrium reaction HCO₃⁻(aq) + H₂O(l) ⇌ H₂CO₃(aq) + OH⁻(aq), which statement correctly identifies a Brønsted-Lowry acid and its conjugate base?

A) Acid: HCO₃⁻, Conjugate Base: OH⁻

B) Acid: H₂O, Conjugate Base: OH⁻

C) Acid: H₂CO₃, Conjugate Base: H₂O

D) Acid: HCO₃⁻, Conjugate Base: H₂CO₃

Correct Answer: B

In the forward reaction, H₂O donates a proton to HCO₃⁻, thus H₂O acts as the Brønsted-Lowry acid. After donating the proton, it becomes OH⁻, which is its conjugate base. Therefore, H₂O and OH⁻ form an acid-conjugate base pair.

In the reversible reaction H₂S(aq) + CN⁻(aq) ⇌ HS⁻(aq) + HCN(aq), which two species are acting as Brønsted-Lowry bases?

A) H₂S and HCN

B) CN⁻ and HS⁻

C) H₂S and HS⁻

D) CN⁻ and HCN

Correct Answer: B

A Brønsted-Lowry base is a proton acceptor. In the forward reaction, CN⁻ accepts a proton from H₂S to form HCN. In the reverse reaction, HS⁻ accepts a proton from HCN to form H₂S. Therefore, CN⁻ and HS⁻ are the two species acting as bases in this equilibrium.

Identify the two conjugate acid-base pairs in the reaction: H₂PO₄⁻(aq) + NH₃(aq) ⇌ HPO₄²⁻(aq) + NH₄⁺(aq)

A) (H₂PO₄⁻ / HPO₄²⁻) and (NH₃ / NH₄⁺)

B) (H₂PO₄⁻ / NH₄⁺) and (NH₃ / HPO₄²⁻)

C) (H₂PO₄⁻ / NH₃) and (HPO₄²⁻ / NH₄⁺)

D) (H₂PO₄⁻ / H₃PO₄) and (NH₃ / NH₂⁻)

Correct Answer: A

A conjugate acid-base pair differs by one proton. In the forward reaction, the acid H₂PO₄⁻ donates a proton to become its conjugate base, HPO₄²⁻. The base NH₃ accepts that proton to become its conjugate acid, NH₄⁺. Therefore, the two pairs are (H₂PO₄⁻ / HPO₄²⁻) and (NH₃ / NH₄⁺).