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AP Chemistry Practice Quiz: Buffer Capacity

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

Test your understanding with short quizzes. This quiz has 9 questions to check your progress.

Question 1 of 9

A chemist prepares a buffer solution. If the concentrations of both the conjugate acid and conjugate base components are doubled while their ratio is kept constant, which of the following statements is true?

All Questions (9)

A chemist prepares a buffer solution. If the concentrations of both the conjugate acid and conjugate base components are doubled while their ratio is kept constant, which of the following statements is true?

A) The pH remains the same, but the buffer capacity increases.

B) The pH increases, and the buffer capacity increases.

C) The pH remains the same, but the buffer capacity decreases.

D) The pH decreases, and the buffer capacity remains the same.

Correct Answer: A

According to the provided content, increasing the concentration of buffer components while maintaining their ratio increases the buffer's capacity but does not change its pH. The pH is determined by the ratio of the components, which remains unchanged.

Consider two buffer solutions. Solution X contains 0.1 M HA and 0.1 M A⁻. Solution Y contains 0.5 M HA and 0.5 M A⁻. Which statement correctly compares the two solutions?

A) Solution Y has a higher pH than Solution X.

B) Solution X has a greater buffer capacity than Solution Y.

C) Both solutions have the same pH, but Solution Y has a greater buffer capacity.

D) Both solutions have the same buffer capacity, but Solution X has a lower pH.

Correct Answer: C

The pH of a buffer depends on the ratio of the conjugate acid to the conjugate base. Since the ratio is 1:1 in both solutions, their pH values are the same. However, buffer capacity is determined by the absolute concentrations of the components. Solution Y has higher concentrations, so it has a greater capacity to neutralize added acid or base.

A buffer solution is prepared with a higher concentration of the conjugate base than the conjugate acid. This buffer will have a greater capacity to neutralize which of the following?

A) Added acid

B) Added base

C) Both added acid and added base equally

D) Neither added acid nor added base

Correct Answer: A

As stated in the content, a buffer with more conjugate base than acid has a greater capacity for added acid. The excess conjugate base (A⁻) is available to react with and neutralize incoming H⁺ ions from the added acid.

Which of the following buffer solutions has the greatest capacity to neutralize an added strong base?

A) 0.1 M HA and 0.5 M A⁻

B) 0.5 M HA and 0.1 M A⁻

C) 0.2 M HA and 0.2 M A⁻

D) 0.1 M HA and 0.1 M A⁻

Correct Answer: B

The capacity to neutralize an added base depends on the amount of the conjugate acid (HA) present in the buffer. Comparing the options, Option B has the highest concentration of the conjugate acid (0.5 M HA). Therefore, it has the greatest capacity for neutralizing an added base.

A buffer is designed to have a greater capacity for added base than for added acid. How must the concentrations of the buffer components relate to each other?

A) The concentration of the conjugate acid must be greater than the concentration of the conjugate base.

B) The concentration of the conjugate base must be greater than the concentration of the conjugate acid.

C) The concentrations of the conjugate acid and conjugate base must be equal.

D) The total concentration of both components must be less than 1.0 M.

Correct Answer: A

The provided content explicitly states: 'A buffer with more conjugate acid than base has a greater capacity for added base.' The conjugate acid component is responsible for neutralizing added base.

A chemist has a buffer solution containing 0.2 M of a weak acid (HA) and 0.2 M of its conjugate base (A⁻). To modify the buffer so it has a greater capacity for added acid, what change should be made?

A) Increase the concentration of HA only.

B) Increase the concentration of A⁻ only.

C) Decrease the concentration of both components equally.

D) Add water to dilute the solution.

Correct Answer: B

To increase the capacity for added acid, the concentration of the component that neutralizes acid must be increased. The conjugate base (A⁻) reacts with added acid (H⁺). Therefore, increasing the concentration of A⁻ will increase the buffer's capacity for added acid.

Which statement accurately describes the relationship between component concentrations and buffer capacity?

A) Buffer capacity is solely determined by the ratio of the conjugate acid to the conjugate base.

B) Increasing the absolute concentrations of the buffer components, while keeping the ratio constant, increases the buffer capacity.

C) A buffer's capacity is greatest when the concentration of one component is significantly higher than the other.

D) Diluting a buffer solution increases its capacity to resist pH changes.

Correct Answer: B

This question directly tests the principle that increasing the concentration of buffer components increases the buffer's capacity. Higher concentrations mean more moles are available to react with added acid or base, thus increasing the buffer's overall capacity.

A chemical process is expected to release a significant amount of a strong acid. Which of the following buffer solutions would be the LEAST effective at maintaining a stable pH?

A) A solution with 0.5 M conjugate acid and 0.5 M conjugate base.

B) A solution with 0.1 M conjugate acid and 0.5 M conjugate base.

C) A solution with 0.5 M conjugate acid and 0.1 M conjugate base.

D) A solution with 1.0 M conjugate acid and 1.0 M conjugate base.

Correct Answer: C

To neutralize a strong acid, the buffer needs a sufficient amount of its conjugate base component. According to the content, a buffer with more conjugate base has a greater capacity for added acid. Therefore, the solution with the lowest concentration of conjugate base (Option C, 0.1 M) would be the least effective at neutralizing the added strong acid.

A student claims that two buffer solutions, one made with 0.1 M HA / 0.5 M A⁻ and another with 0.2 M HA / 1.0 M A⁻, have the same pH but different buffer capacities. Is this claim correct?

A) No, the pH values are different, but the capacities are the same.

B) No, both the pH values and the buffer capacities are different.

C) Yes, the pH is the same because the ratio of base to acid is 5:1 in both, but the second solution has a higher capacity due to higher concentrations.

D) Yes, the pH is the same, but the first solution has a higher capacity because the concentrations are lower.

Correct Answer: C

The pH of a buffer is determined by the ratio of [A⁻]/[HA]. In the first solution, the ratio is 0.5/0.1 = 5. In the second, it is 1.0/0.2 = 5. Since the ratios are identical, the pH is the same. However, the second solution has higher absolute concentrations of both components, meaning it has a greater buffer capacity to neutralize added acid or base.