Question 1

What is the Henderson-Hasselbalch equation?

Accepted Answer

The Henderson-Hasselbalch equation is pH = pKa + log([A⁻]/[HA]), where [A⁻] is the conjugate base concentration and [HA] is the weak acid concentration. It relates the pH of a buffer to the pKa and the ratio of base to acid.

Question 2

What is a buffer solution?

Accepted Answer

A buffer solution resists changes in pH when small amounts of acid or base are added. It consists of a weak acid and its conjugate base (or a weak base and its conjugate acid). Buffers are most effective within ±1 pH unit of the pKa.

Question 3

What is the effective buffer range?

Accepted Answer

A buffer is most effective when pH is within ±1 of the pKa (i.e., when the [A⁻]/[HA] ratio is between 0.1 and 10). Outside this range, the buffer cannot effectively resist pH changes.

Question 4

What is pKa?

Accepted Answer

pKa = -log₁₀(Ka), where Ka is the acid dissociation constant. A lower pKa means a stronger acid. Common values: acetic acid 4.76, carbonic acid 6.35, ammonium 9.25.

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