AP Chemistry Quiz: Buffer Capacity

What this quiz covers

This quiz focuses on Buffer Capacity, giving you a quick way to practice the rules, question types, and explanations that matter most for AP Chemistry.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

Question 1

1. Buffer B, because it contains more conjugate base
2. Buffer A, because it contains more weak acid to neutralize added base (correct answer)
3. They will change equally because the total concentration of buffer components is the same
4. Buffer B, because buffers are most effective when one component is in large excess
5. They will change equally because both use the same conjugate pair

Explanation: This question tests your understanding of buffer capacity. Buffer capacity indicates resistance to added base, relying on the total concentrations of weak acid and conjugate base to neutralize OH⁻. Higher weak acid concentrations better handle base additions. Capacity depends on these levels and the ratio's proximity to 1:1. A tempting distractor is that they will change equally because the total concentration of buffer components is the same, but Buffer A's balanced ratio and higher acid give better capacity. A transferable strategy is, for base additions, to seek higher weak acid concentration and balanced ratio; this means greater capacity to absorb added OH⁻.

Question 2

1. Buffer A, because sulfite-based buffers are inherently stronger than phosphate-based buffers
2. Buffer B, because it contains a greater amount of both buffer components (correct answer)
3. They have equal capacity because both are prepared with equal conjugate pair concentrations
4. They have equal capacity because the same amount of strong acid is added
5. Buffer A, because lower concentration buffers change pH less

Explanation: This question tests your understanding of buffer capacity. Buffer capacity measures a buffer's ability to resist acid additions, relying on total concentrations of the buffer pair to neutralize H⁺. Higher concentrations mean more effective neutralization with less pH change. Capacity depends on these levels, independent of the specific pair for similar conditions. A tempting distractor is that they have equal capacity because both are prepared with equal conjugate pair concentrations, but this misses Buffer B's doubled concentrations providing greater capacity. A transferable strategy is to evaluate total buffer concentrations across different pairs; higher total concentration means greater capacity to absorb added acid or base.

Question 3

1. Buffer B, because it contains more moles of both HA and $A^{-}$ per liter (correct answer)
2. They have equal capacity because their HA:$A^{-}$ ratios are equal
3. Buffer A, because dilute solutions have fewer particles that can change pH
4. They have equal capacity because the same amount of strong acid is added
5. Buffer A, because lower concentration means smaller pH change for any reaction

Explanation: This question tests your understanding of buffer capacity. Buffer capacity measures resistance to pH change from added acid, based on total concentrations of weak acid and conjugate base to neutralize $H^{+}$. Higher concentrations allow greater neutralization without large shifts. Capacity hinges on these levels, not merely the ratio. A tempting distractor is that they have equal capacity because their HA:$A^{-}$ ratios are equal, but this is wrong as Buffer B's higher concentrations provide better capacity. A transferable strategy is to compare total concentrations of buffer components; higher total concentration means greater capacity to absorb added acid or base.

Question 4

1. Buffer 2, because it has more weak acid overall
2. Buffer 1, because it has more conjugate base available to consume added acid (correct answer)
3. Buffer 2, because unequal amounts of components always increase buffer capacity
4. They resist equally because both contain the same total moles of buffer components
5. They resist equally because both contain a weak acid and its conjugate base

Explanation: This question tests your understanding of buffer capacity. Buffer capacity assesses a buffer's ability to resist added acid, depending on the total moles of conjugate base available to neutralize H⁺. Greater moles mean more acid can be handled with minimal ratio change. It's these absolute amounts, not just the ratio, that define capacity. A tempting distractor is that they resist equally because both contain the same total moles of buffer components, but this overlooks Buffer 1's higher conjugate base moles offering superior resistance. A transferable strategy is, when adding acid, to evaluate the amount of conjugate base; higher amounts mean greater capacity to absorb added H⁺.

Question 5

1. Buffer 1, because it starts with more weak acid
2. Buffer 2, because it has more conjugate base available to consume added acid (correct answer)
3. Buffer 1, because unequal concentrations always increase buffer capacity
4. They will change equally because their total buffer concentration is the same
5. They will change equally because they contain the same conjugate pair

Explanation: This question tests your understanding of buffer capacity. Buffer capacity describes a buffer's resistance to pH change from added acid, depending on the total amount of conjugate base available to neutralize H⁺, alongside the weak acid. Equal total concentrations but different ratios affect capacity, with more conjugate base better for acid additions. Capacity isn't just about the ratio but the quantities ready to react. A tempting distractor is that they will change equally because their total buffer concentration is the same, but this is incorrect as Buffer 2's higher conjugate base and 1:1 ratio give it superior capacity. A transferable strategy is, for acid additions, to look for higher concentrations of conjugate base; this means greater capacity to absorb added H⁺.

Question 6

1. Buffer 3, because having excess $\mathrm{HA}$ prevents any change in pH when acid is added
2. Buffer 2, because dilute buffers have fewer ions and therefore change pH less
3. Buffer 1, because it contains the greatest total amount of buffering components ($\mathrm{HA}$ and $\mathrm{A^-}$) (correct answer)
4. Buffer 2, because equal moles of $\mathrm{HA}$ and $\mathrm{A^-}$ always guarantee the greatest buffer capacity
5. Buffer 1, because its initial pH must be closer to neutral than the others

Explanation: Buffer capacity is the measure of a buffer's ability to resist pH changes upon addition of acid or base. It depends on the total amount of weak acid (HA) and conjugate base (A⁻) available to neutralize added H⁺ or OH⁻, with higher total moles providing greater resistance. For adding acid, the amount of A⁻ is crucial as it reacts with H⁺ to form HA, but overall capacity increases with the total buffering components. The ratio of HA to A⁻ affects the initial pH and the symmetry of capacity, but it's the absolute quantities that determine how much addition can be absorbed. A tempting distractor is that equal moles of HA and A⁻ always guarantee the greatest capacity, but this ignores that dilute solutions with equal ratios have less total material than concentrated ones. To evaluate buffer capacity, compare the total moles of buffering species, as higher total concentration means greater capacity to absorb added acid or base.

Question 7

1. Buffer S has greater capacity because its components are present in a smaller total amount, so the buffer is less likely to be overwhelmed
2. Buffer S has greater capacity because the NO$_2^-$:HNO$_2$ ratio is the same as in Buffer T
3. Buffer T has greater capacity because it contains more total moles of buffering components to react with added H$^+$ (correct answer)
4. Both buffers have the same capacity because they have the same NO$_2^-$:HNO$_2$ ratio
5. Both buffers have the same capacity because they use the same conjugate acid–base pair

Explanation: This question tests understanding of buffer capacity. Buffer capacity depends on the total amount of acid and conjugate base available to neutralize added H⁺ or OH⁻, not just the ratio of components. Buffer T contains 0.50 mol HNO₂ and 1.50 mol NO₂⁻ (2.0 mol total), while Buffer S contains only 0.050 mol HNO₂ and 0.150 mol NO₂⁻ (0.20 mol total). When strong acid is added, it reacts with the conjugate base NO₂⁻, and Buffer T has ten times more conjugate base available to neutralize the added H⁺. The misconception in choice D is that having the same ratio (1:3 in both buffers) means equal capacity, but this ignores the importance of total amount. To determine buffer capacity, always compare the total moles of buffering components available to react with added acid or base.

Question 8

1. Buffer Q, because it has more total moles of $\mathrm{HA}$ available to neutralize added $\mathrm{OH^-}$ (correct answer)
2. Both buffers, because buffer capacity depends only on the $\mathrm{A^-:HA}$ ratio, not the total amount
3. Both buffers, because equal volumes always have equal buffer capacity
4. Buffer P, because lower concentrations reduce the extent of reaction with added base
5. Buffer P, because its pH begins closer to the $pK_a$ than Buffer Q

Explanation: Buffer capacity measures a solution's ability to minimize pH changes upon acid or base addition. It depends on the total moles of buffering agents available to react with and neutralize H⁺ or OH⁻, beyond just their concentration ratio. Higher total amounts allow the buffer to handle more addition before capacity is exceeded. While ratios affect pH positioning, capacity scales directly with the quantity of components. A tempting distractor is that equal volumes imply equal capacity, but this disregards differences in concentrations and total moles. To compare capacities, evaluate total buffering moles, as higher total concentration means greater ability to absorb added acid or base.

Question 9

1. Buffer M has greater capacity because lower concentration minimizes reaction with added acid
2. Buffer N has greater capacity because it contains more total buffering species to convert added $\mathrm{H^+}$ into $\mathrm{HA}$ (correct answer)
3. Both buffers have equal capacity because the $[\mathrm{A^-}]/[\mathrm{HA}]$ ratio is the same
4. Both buffers have equal capacity because the identity of the conjugate pair fixes the capacity
5. Buffer M has greater capacity because its initial pH must be lower than Buffer N

Explanation: Buffer capacity quantifies resistance to pH changes in buffers upon acid or base addition. It depends on the total amount of buffering species available for neutralization, independent of their ratio alone. Buffers with identical ratios but different totals vary in capacity, with higher totals being superior. The ratio fixes the pH, but total concentration determines neutralization extent. A common misconception is that same ratios mean equal capacity, but this fails to account for differences in total moles. When evaluating buffers, compare total concentrations, as higher total amounts provide greater capacity to absorb added acid or base.

Question 10

1. Buffer 2, because it has more conjugate acid available to neutralize added base (correct answer)
2. Buffer 1, because it has more weak base
3. They will change equally because the total concentration is the same
4. They will change equally because both contain the same conjugate pair
5. Buffer 1, because buffers resist all additions of base equally well

Explanation: This question tests your understanding of buffer capacity. Buffer capacity indicates how well a buffer handles added base, depending on the total concentrations of weak base and conjugate acid available to neutralize OH⁻. More conjugate acid better resists base by converting to base. It's the absolute amounts, not just ratio, that matter. A tempting distractor is that they will change equally because the total concentration is the same, but this ignores Buffer 2's higher conjugate acid better suiting base addition. A transferable strategy is, for base additions, to look for higher conjugate acid concentration; this means greater capacity to absorb added OH⁻.

Question 11

1. Buffer 2, because it contains more weak acid relative to base
2. Buffer 1, because it has more conjugate base available to neutralize added acid (correct answer)
3. They will change equally because both contain the same moles of HCN
4. They will change equally because HCN is a weak acid in both buffers
5. Buffer 2, because a smaller amount of conjugate base makes the buffer stronger

Explanation: This question tests your understanding of buffer capacity. Buffer capacity indicates how much acid a buffer can neutralize while keeping pH stable, depending on the total moles of conjugate base available to react with H⁺. More moles of conjugate base mean better resistance without large ratio changes. Capacity relies on these absolute amounts, not merely the ratio. A tempting distractor is that they will change equally because both contain the same moles of HCN, but this ignores Buffer 1's higher conjugate base moles offering better capacity. A transferable strategy is, when adding acid, to check the amount of conjugate base; higher amounts mean greater capacity to absorb added H⁺.

Question 12

1. Buffer B has greater capacity because a smaller amount of solution changes pH less when base is added.
2. Buffer A has greater capacity because it contains more total moles of the weak acid and its conjugate base to neutralize added base. (correct answer)
3. Buffer B has greater capacity because the weak acid is present, and only the acid matters when base is added.
4. Both have equal capacity because the $\mathrm{H_3PO_4/H_2PO_4^-}$ pair fixes the pH regardless of amount.
5. Buffer A has lower capacity because larger amounts of buffer components shift equilibrium more, causing larger pH changes.

Explanation: This question evaluates buffer capacity principles. Buffer capacity is determined by the total moles of weak acid and conjugate base available to neutralize added H⁺ or OH⁻, not by solution volume or other factors. Buffer A contains relatively large amounts of both H₃PO₄ and H₂PO₄⁻, while Buffer B has relatively small amounts of both. When strong base is added, the H₃PO₄ (weak acid) will react to neutralize the OH⁻ ions, and Buffer A has more moles of H₃PO₄ available for this reaction. The misconception in choice A is that smaller amounts somehow change pH less, but this confuses dilution effects with buffer capacity. The key principle is that higher total concentration of buffer components provides greater capacity to resist pH changes from added acid or base.

Question 13

1. Buffer B will have the smaller pH change because equal amounts of acid and base maximize buffering.
2. Both buffers will have the same pH change because they have the same $\mathrm{HF:F^-}$ ratio.
3. Buffer A will have the smaller pH change because it contains more total moles of buffering components. (correct answer)
4. Buffer A will have the larger pH change because concentrated solutions respond more strongly to added base.
5. Neither buffer will resist added base because $\mathrm{HF}$ is an acid, not a base.

Explanation: This question assesses buffer capacity concepts. Buffer capacity is determined by the total amount of weak acid and conjugate base available to neutralize added H⁺ or OH⁻, not by the ratio alone. Buffer A contains much more total HF and F⁻ than Buffer B, even though both have equal amounts of acid and base within each buffer. When NaOH is added, the HF in each buffer will react to neutralize the OH⁻ ions, and Buffer A has more HF available for this neutralization. The misconception in choice B is that buffers with the same ratio will show the same pH change, but this ignores the crucial role of total concentration. Remember that greater total concentration of buffer components provides greater capacity to resist pH changes from added acid or base.

Question 14

1. Buffer 2, because it contains more total phosphate species
2. Buffer 1, because it contains more HPO$_4^{2-}$ available to react with added H$^+$ (correct answer)
3. Buffer 2, because it contains more H$_2$PO$_4^-$, which is the acid form
4. Both buffers, because phosphate buffers are effective over a wide range
5. Both buffers, because the ratio of conjugate base to acid is the only factor that matters for capacity

Explanation: This question tests understanding of buffer capacity. Buffer capacity depends on the total amount of weak acid and conjugate base available to neutralize added H⁺ or OH⁻, not just their ratio. When HCl is added, the conjugate base (HPO₄²⁻) reacts with H⁺ to form H₂PO₄⁻, so we need sufficient HPO₄²⁻ to neutralize the added acid. Buffer 1 has 0.20 mol HPO₄²⁻ while Buffer 2 has only 0.10 mol HPO₄²⁻, making Buffer 1 twice as capable of resisting pH change. The distractor about more total phosphate (option A) is incorrect because it's specifically the amount of conjugate base that matters for neutralizing added acid. The key strategy is that higher total concentration of buffer components means greater capacity to absorb added acid or base.

Question 15

1. Buffer A, because nitrous acid is a weaker acid than hypochlorous acid
2. Buffer B, because it has higher concentrations of both buffer components (correct answer)
3. Buffer A, because different conjugate pairs cannot be compared for capacity
4. They have equal capacity because both are prepared with equal acid and base concentrations
5. They have equal capacity because the same amount of strong acid is added

Explanation: This question tests your understanding of buffer capacity. Buffer capacity assesses resistance to pH change from added acid, based on total concentrations of weak acid and conjugate base available for neutralization. Higher concentrations provide more components to react, minimizing ratio shifts. Different pairs can be compared by their concentrations, not just Ka values. A tempting distractor is that they have equal capacity because both are prepared with equal acid and base concentrations, but this is wrong as Buffer B's higher concentrations yield greater capacity. A transferable strategy is to compare total concentrations regardless of the specific pair; higher total concentration means greater capacity to absorb added acid or base.

Question 16

1. Buffer A, because a concentrated buffer contains more total buffering species to consume added $\mathrm{H^+}$ (correct answer)
2. Buffer B, because fluoride ions neutralize strong acids more completely than acetate ions
3. Both buffers, because buffer capacity depends only on having a 1:1 acid-to-base ratio
4. Both buffers, because any buffer neutralizes the same amount of strong acid regardless of concentration
5. Buffer B, because $\mathrm{HF}$ is a stronger weak acid than $\mathrm{CH_3COOH}$

Explanation: Buffer capacity quantifies a buffer's resistance to pH changes from added acid or base. It is determined by the total quantities of acid and base available for neutralization, where more material allows greater absorption of H⁺ or OH⁻. Different conjugate pairs may have varying strengths, but capacity fundamentally scales with the total amount present, not just the acid's Ka. For equal volumes, concentrated buffers outperform dilute ones due to higher moles of components. A tempting distractor is that capacity depends only on a 1:1 ratio, but this ignores that total concentration is key for actual neutralization ability. To assess buffer effectiveness, focus on total concentrations, as higher total amounts mean greater capacity to handle added acid or base.

Question 17

1. Buffer 1 will have greater capacity because its components are present in equal concentrations
2. Buffer 2 will have greater capacity because it contains a larger total concentration of buffering species (correct answer)
3. Both buffers will have equal capacity because they have the same HA:A$^-$ ratio
4. Buffer 1 will have greater capacity because concentrated solutions have larger pH changes
5. Both buffers will have equal capacity because the same strong acid is added to each

Explanation: This question tests understanding of buffer capacity. Buffer capacity depends on the total amount of acid and conjugate base available to neutralize added H⁺ or OH⁻, which is determined by both concentration and volume. Buffer 2 has concentrations of 0.50 M for both HA and A⁻, while Buffer 1 has 0.25 M for each component. Since both buffers have the same volume, Buffer 2 contains twice as many total moles of buffering species. When strong acid is added, it reacts with A⁻, and Buffer 2 has twice as much A⁻ available to neutralize the H⁺. The misconception in choice A is that equal concentrations of components means maximum capacity, but higher total concentration means greater capacity to absorb added acid or base.

Question 18

1. Buffer 2, because it contains more BH$^+$ to neutralize added acid
2. Buffer 1, because it contains more weak base to neutralize added acid (correct answer)
3. They will change equally because the total buffer concentration is the same
4. They will change equally because both contain a weak base/conjugate acid pair
5. Buffer 2, because buffers work best when conjugate acid is in excess for any addition

Explanation: This question tests your understanding of buffer capacity. Buffer capacity indicates resistance to added acid, depending on the total concentrations of weak base available to neutralize H⁺. Higher weak base concentrations better handle acid without major shifts. It's the amounts, not just ratio, that count. A tempting distractor is that they will change equally because the total buffer concentration is the same, but this ignores Buffer 1's higher weak base better suiting acid addition. A transferable strategy is, for acid additions to basic buffers, to look for higher weak base concentration; this means greater capacity to absorb added H⁺.

Question 19

1. Buffer B, because it contains more acetic acid
2. Buffer A, because it contains more acetate ion to react with added acid (correct answer)
3. They resist equally because both contain acetic acid
4. They resist equally because Buffer B is more concentrated overall
5. Buffer B, because a larger acid-to-base ratio always increases buffer capacity

Explanation: This question tests your understanding of buffer capacity. Buffer capacity reflects resistance to added acid, relying on the total amounts of weak acid and conjugate base available to neutralize H⁺. Higher levels mean more H⁺ can be absorbed without significant ratio change. Capacity depends on these quantities, not solely the ratio. A tempting distractor is that they resist equally because Buffer B is more concentrated overall, but this misses that Buffer A's balanced and higher conjugate base better resists acid. A transferable strategy is, for acid additions, to prioritize buffers with higher conjugate base concentration; this means greater capacity to absorb added H⁺.

Question 20

1. Buffer 2
2. They will change equally because the acid-to-base ratio is the same
3. Buffer 1 (correct answer)
4. They will change equally because both contain a weak acid
5. Buffer 2, because lower concentration buffers are less affected by added base

Explanation: This question tests your understanding of buffer capacity. Buffer capacity measures a buffer's ability to resist pH shifts when adding base, depending on the total concentrations of weak acid and conjugate base to neutralize OH⁻. Greater concentrations allow more neutralization with less impact on the ratio. It's the overall levels, not just the ratio, that determine this resistance. A tempting distractor is that they will change equally because the acid-to-base ratio is the same, but this is incorrect because Buffer 1's higher concentrations provide superior capacity. A transferable strategy is to evaluate total buffer concentrations; higher total concentration means greater capacity to absorb added acid or base.