Henderson-Hasselbalch Calculator

This calculator finds the pH of a buffer solution using the Henderson-Hasselbalch equation, the essential tool for working with buffers in chemistry and biology. A buffer is a solution that resists changes in pH when small amounts of acid or base are added, made from a weak acid and its conjugate base in comparable amounts. Buffers are vital wherever a stable pH matters: in living systems, where blood is buffered to stay near pH 7.4, in laboratory and industrial chemistry, in pharmaceuticals, and in aquariums and fermentation. The Henderson-Hasselbalch equation gives the pH of such a buffer directly from two pieces of information: the pKa of the weak acid, which reflects its strength, and the ratio of the conjugate base to the acid. This tool computes it. You enter the pKa and the concentrations of the conjugate base and the weak acid, and the calculator returns the pH of the buffer, along with the base-to-acid ratio, the pKa for reference, and the corresponding pOH. The results update as you type, so you can see how changing the ratio shifts the pH. Use it to prepare a buffer at a target pH, to predict the pH of a buffer mixture, or for chemistry and biochemistry study. The equation is pH equals pKa plus the base-ten logarithm of the ratio of conjugate base to weak acid. A key insight it makes clear is that when the concentrations of acid and base are equal, the ratio is one and its logarithm is zero, so the pH equals the pKa exactly, the point of maximum buffering capacity. Adjusting the ratio either side of this shifts the pH up or down, which is how a buffer is tuned to a desired value. The equation assumes a true buffer with both species present in reasonable amounts.

pH = pKa + log10([A-]/[HA]). When base and acid concentrations are equal, pH equals pKa, the point of best buffering. Assumes a true buffer with both species present.