Explore the relationship between pKa, pH, and buffer capacity using the Henderson-Hasselbalch equation. Visualize how adding strong acid or base affects your buffer.
Enter buffer parameters to explore the relationship between pKa, pH, and buffer capacity
pH = pKa + log₁₀([A⁻]/[HA])
This equation relates the pH of a buffer solution to the pKa of the weak acid and the ratio of conjugate base [A⁻] to weak acid [HA]. When the ratio is 1:1, pH = pKa.
pKa = -log₁₀(Ka) where Ka is the acid dissociation constant. It measures the strength of a weak acid:
Buffer capacity measures how well a buffer resists pH changes. It's defined as the amount of acid or base needed to change the pH by one unit.
pKa ± 1 pH unit
Buffers work effectively within one pH unit of the pKa. This corresponds to:
Adding Strong Acid (H⁺):
A⁻ + H⁺ → HA (converts base to acid, pH decreases)
Adding Strong Base (OH⁻):
HA + OH⁻ → A⁻ + H₂O (converts acid to base, pH increases)
| Buffer | pKa | Range |
|---|---|---|
| Acetate | 4.76 | 3.8 - 5.8 |
| Phosphate (pKa₂) | 7.20 | 6.2 - 8.2 |
| Tris | 8.06 | 7.0 - 9.0 |
| Ammonium | 9.25 | 8.3 - 10.3 |
| Carbonate (pKa₂) | 10.33 | 9.3 - 11.3 |
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