Buffer pH Calculator (Henderson-Hasselbalch)

The Henderson-Hasselbalch equation gives a buffer's pH.

How the Math Works

The Henderson-Hasselbalch equation reveals the mathematical relationship between a buffer's pH, its pKa, and the ratio of conjugate base (A⁻) to weak acid (HA). When you input the pKa and acid/base ratio, the calculator applies the formula pH = pKa + log₁₀([A⁻] ÷ [HA]). The logarithmic term adjusts the pKa value: when equal amounts of acid and base are present, the log of 1 equals zero, making pH = pKa. If you have more base than acid, the log becomes positive, raising the pH above pKa; more acid produces a negative log value, lowering the pH below pKa.

Practical Applications

To use this calculator in practice, first determine the pKa of your buffer system from reference tables or literature. Then measure or calculate the concentrations of the conjugate base (A⁻) and weak acid (HA) in your solution. Simply enter these values into the calculator: input the pKa value and divide the concentration of base by the concentration of acid to get the ratio. The calculator instantly computes the resulting pH, eliminating tedious manual logarithmic calculations and reducing potential for errors in experimental work.

Day-to-Day Use

Buffer pH calculations impact many everyday technologies and experiences. The saliva in your mouth maintains a near-neutral pH through natural buffering systems, preventing dangerous acidity that could damage teeth or tissues. In laboratories, researchers use buffer solutions to stabilize pH during DNA extraction, drug synthesis, and biological assays. Food scientists rely on buffer calculations when creating carbonated beverages, where maintaining proper acidity ensures consistent taste and prevents spoilage. Even pool maintenance requires buffer pH calculations to keep swimming waters safe and enjoyable by preventing eye irritation and skin problems.

Worked example

pKa 4.76, equal concentrations → pH 4.76.

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