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Properties of Buffers

A buffer resists pH change because it contains a reservoir of both a weak acid and its conjugate base. Added base is neutralized by the weak acid; added acid is neutralized by the conjugate base. For this to work, both components must be present in significant amounts — a buffer is not just a weak acid alone.

UNIT 8 TOPIC 8.8 • PROPERTIES OF BUFFERS CHOOSING A BUFFER A buffer needs appreciable amounts of BOTH a weak acid (HA) and its conjugate base (A⁻). USEFUL BUFFER RANGE (pKa ± 1) buffering possible here pKa − 2 pKa − 1 pKa pKa + 1 pKa + 2 Needs both forms HA is the acidic component; A⁻ is the basic component. A⁻ neutralizes added H⁺ A⁻ + H⁺ → HA HA neutralizes added OH⁻ HA + OH⁻ → A⁻ + H₂O Each form mops up one kind of added strong species. Best buffering capacity Maximum buffering when [HA] ≈ [A⁻] (pH = pKa) Higher total concentration → greater capacity. At the half-equivalence point [HA] = [A⁻], so pH = pKa — the buffer resists change most. Choosing the pair Pick a weak acid whose pKa is within ±1 of the target pH. useful range = pKa ± 1 Example weak acids: acetic acid pKa 4.7 dihydrogen phosphate pKa 7.2 ammonium pKa 9.2 Match the pair to your target pH. HENDERSON–HASSELBALCH pH = pKa + log ( [A⁻] / [HA] ) when [A⁻] = [HA], log(1) = 0, so pH = pKa AP Chemistry · Unit 8 · Acids and Bases
A buffer resists pH change because it holds a reservoir of both a weak acid and its conjugate base: the acid neutralizes added base, and the conjugate base neutralizes added acid. Both components must be present in significant amounts for buffering to work.
Buffer Reservoir · Open the sandbox →

The traps mis-explain why a buffer is stable (it is the two-way neutralizing reservoir, not any single component) and misunderstand its composition (both the weak acid and its conjugate base must be present). Remove one component and the buffering fails.

The work

3 ways in · any order
Lesson
Properties of Buffers ›

A buffer resists pH change through a reservoir of both a weak acid and its conjugate base. The lesson explains the mechanism and composition, then closes with a ten-scenario check.

Skill check · 10 scenarios
Open lesson →
Diagnostic
10-item topic check ›

Ten items spanning the Topic 8.8 misconceptions: buffer stability mis-explained, and buffer composition misunderstood (both components required).

Not started · 10 items · ~15 min
Start diagnostic →
Targeted Practice
Drill a single misconception ›

Pick one of the failure modes you missed and drill it on its own. The round is adaptive: two correct in a row clears the misconception and moves you to the next.

Take the diagnostic to identify your misconceptions
Diagnostic first