Henderson-Hasselbalch Buffer Preparation Calculator

Henderson-Hasselbalch Buffer Preparation Calculator

Buffer Properties

Component Molecular Weights

g/mol
g/mol

Buffer Solutions & Henderson-Hasselbalch

A buffer solution is an aqueous solution consisting of a mixture of a weak acid (HA) and its conjugate base (A⁻), or a weak base and its conjugate acid. Its key property is the ability to resist significant changes in pH upon the addition of small amounts of strong acid or strong base. This is crucial for maintaining stable pH environments in biological systems and chemical experiments.

The Henderson-Hasselbalch equation is fundamental for preparing buffers and understanding their behavior:

pH = pKa + log₁₀([A⁻]/[HA])

Where:
• pH is the desired pH of the buffer.
• pKa is the acid dissociation constant of the weak acid (the pH at which [HA] = [A⁻]).
• [A⁻] is the molar concentration of the conjugate base.
• [HA] is the molar concentration of the weak acid.

This calculator uses the equation to determine the required ratio of [A⁻]/[HA] for your target pH. Combined with the desired total buffer concentration and volume, it calculates the specific mass of the weak acid and conjugate base components you need to weigh out.

Frequently Asked Questions

What is the effective buffering range?

A buffer is most effective at resisting pH changes when the pH of the solution is close to the pKa of the weak acid. The generally accepted effective buffering range is within ±1 pH unit of the pKa (i.e., from pKa - 1 to pKa + 1). Within this range, there are significant amounts of both the weak acid and its conjugate base present to neutralize added H⁺ or OH⁻. Outside this range, the buffer's capacity diminishes rapidly. This calculator will provide a warning if your target pH is outside this optimal range.

What's the difference between buffer capacity and buffer range?

• Buffer Range: The pH range over which the buffer effectively resists pH changes (typically pKa ± 1). It depends primarily on the pKa of the weak acid.
• Buffer Capacity: The amount of strong acid or strong base that can be added to the buffer before the pH changes significantly. It depends on the total concentration of the buffer components ([HA] + [A⁻]). A more concentrated buffer has a higher capacity.

Can I use a weak base and its conjugate acid instead?

Yes, absolutely. The Henderson-Hasselbalch equation can also be written for a weak base (B) and its conjugate acid (BH⁺): pOH = pKb + log₁₀([BH⁺]/[B]), or equivalently in terms of pH: pH = pKa + log₁₀([B]/[BH⁺]), where pKa refers to the conjugate acid BH⁺ (pKa + pKb = 14). This calculator assumes you are starting with the weak acid (HA) and conjugate base (A⁻) forms, using their respective molar masses, but the underlying principle is the same.