Buffer Calculator

Introduction

A buffer is an aqueous solution able to preserve an approximately constant pH even when exposed to small amounts of acids or bases. To calculate the specific pH of a buffer, you need to use the Henderson-Hasselbalch equation. If the buffer consists of a solution of a weak acid of concentration [HA] and its conjugate base of concentration [A^-] (e.g. acetic acid and sodium acetate), the equation has the form:

Where pK_a is the negative base-10 logarithm of the acid dissociation constant. If the buffer consists of a solution of a weak base of concentration [B] and its conjugate acid of concentration [BH⁺] (e.g. Tris and its protonated form), Henderson-Hasselbalch equation takes the form:

Usage

Buffer Calculator allows you to calculate any of the four values (pH, pK_a, [HA], [A^-]) if you provide the other three values. So in addition to pH value calculations from pK_a and concentrations, the app can also help you to calculate the buffer composition required to obtain a target pH value. As the pH value is determined by the ratio of dissociated and non-dissociated form of the weak acid or base, these concentrations can be easily derived from the required total concentration of the buffer. For example, if we are to prepare a 100 mM sodium acetate buffer solution of pH 4.0, we will first obtain the required ratio of acetate and acetic acid by entering 4.0 for pH, 4.76 for pK_a and e.g. 10 for [A^-]. The calculator will return 57.544 as the [HA] concentration, so the required proportion of acetate in the mixture with acetic acid is 10/(10+57.544) = 0.148. For the total 100 mM concentration we will prepare a solution containing 14.8 mM sodium acetate and 85.2 mM acetic acid.