Practice buffer chemistry problems using the Henderson–Hasselbalch equation: pH = pKa + log₁₀([A⁻]/[HA]). Create multiple scenarios, choose what to solve for, and optionally check your own answers.
Build one or more buffer scenarios by specifying pKa, pH, ratios, or concentrations. Choose what you want to solve for and optionally enter your own answer to check it.
We'll apply the Henderson–Hasselbalch equation for each scenario.
For learning and homework practice only; not for clinical, pharmaceutical, or industrial use.
The Henderson–Hasselbalch equation is fundamental to understanding buffer chemistry. It relates pH to pKa and the concentrations of a weak acid and its conjugate base:
Where:
At this point, [A⁻] = [HA], meaning the acid is 50% dissociated. This is the center of the buffer region and the point of maximum buffer capacity.
More conjugate base than acid is present ([A⁻] > [HA]). The solution becomes increasingly basic as pH rises above pKa.
More acid than conjugate base is present ([HA] > [A⁻]). The solution becomes increasingly acidic as pH drops below pKa.
Buffers work most effectively when pH is within one unit of pKa. In this range, the ratio [A⁻]/[HA] varies from 1:10 to 10:1.
| Buffer System | Acid (HA) | Base (A⁻) | pKa | Buffer Range |
|---|---|---|---|---|
| Acetate | CH₃COOH | CH₃COO⁻ | 4.76 | 3.8–5.8 |
| Phosphate (pKa₂) | H₂PO₄⁻ | HPO₄²⁻ | 7.2 | 6.2–8.2 |
| Bicarbonate | H₂CO₃ | HCO₃⁻ | 6.35 | 5.4–7.4 |
| Tris | Tris-H⁺ | Tris | 8.07 | 7.1–9.1 |
| Ammonia | NH₄⁺ | NH₃ | 9.25 | 8.3–10.3 |
Starting from the acid dissociation equilibrium:
The equilibrium constant Ka is:
Taking the negative log of both sides:
Which rearranges to:
Educational Use Only
This tool is designed for learning and homework practice. It should not be used for clinical, pharmaceutical, or industrial buffer preparation. Real-world applications require consideration of ionic strength, temperature effects, and activity coefficients.
Calculate pH, pOH, [H⁺], and [OH⁻] for acids and bases
Design and analyze buffer solutions with pH targets
Calculate dilution volumes using C₁V₁ = C₂V₂
Convert between Ka and pKa, analyze acid strength
Calculate molarity, moles, mass, and volume
Calculate how to prepare solutions from stock