Henderson-Hasselbalch Calculator

The calculation is rooted in the fundamental buffer equilibrium equation. First, we compute the logarithmic acid dissociation constant from the acid dissociation constant (K_a) using the formula: logK = -log10(K_a), which is equivalent to finding the pK_a. Next, the logarithmic buffer ratio is determined by evaluating the base-to-acid concentration ratio: logBA = log10([Conjugate Base] / [Acid]). Finally, the target pH of the solution is calculated by summing these two components together: pH = logK + logBA.

Let us calculate the pH of a buffer solution where the conjugate base concentration is 0.7 M and the weak acid concentration is 0.5 M, assuming an acid dissociation constant (K_a) of 1.8 x 10^-5. First, we find the logK (pK_a) by taking the negative base-10 logarithm of 1.8 x 10^-5, which yields approximately 4.745. Next, we find the logBA value by dividing the conjugate base by the acid: 0.7 / 0.5 = 1.4, and taking log10(1.4), which gives approximately 0.146. Adding these two values together (4.745 + 0.146) results in a final buffer pH of 4.891.

Always ensure that your concentration inputs for both the weak acid and its conjugate base are expressed in the same units, typically molarity (M), before calculating their ratio. Keep in mind that the Henderson-Hasselbalch equation provides an approximation that works best when the concentrations of the acid and base are significantly higher than the autoionization of water and the dissociation constant is small. For highly dilute solutions or extreme pH ranges near 0 or 14, standard approximations may lose accuracy.