# Buffer Solution Calculator

Free buffer solution calculator using the Henderson-Hasselbalch equation. Calculate pH, pKa, or concentrations for buffer systems.

## What this calculates

Calculate the pH of a buffer solution using the Henderson-Hasselbalch equation: pH = pKa + log([A⁻]/[HA]). Solve for pH, pKa, conjugate base concentration, or weak acid concentration.

## Inputs

- **Solve For** — options: pH, pKa, [A⁻]/[HA] Ratio, [A⁻] Concentration, [HA] Concentration — Select what to calculate.
- **pKa** — min -2, max 16 — pKa of the weak acid (e.g., acetic acid = 4.76).
- **[A⁻] Conjugate Base** (M) — min 0 — Molar concentration of the conjugate base (e.g., acetate).
- **[HA] Weak Acid** (M) — min 0 — Molar concentration of the weak acid (e.g., acetic acid).
- **pH** — min -2, max 16 — pH of the buffer (needed when solving for other variables).

## Outputs

- **Result** — formatted as text — The calculated value.
- **Buffer pH** — The pH of the buffer solution.
- **Formula** — formatted as text — Henderson-Hasselbalch equation and steps.
- **Buffer Region** — formatted as text — Effective buffer range (pKa ± 1).

## Frequently Asked Questions

**Q: What is the Henderson-Hasselbalch equation?**

A: 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.

**Q: What is a buffer solution?**

A: 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.

**Q: What is the effective buffer range?**

A: 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.

**Q: What is pKa?**

A: 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.

---

Source: https://vastcalc.com/calculators/chemistry/buffer-solution
Category: Chemistry
Last updated: 2026-04-21