**Nico Miller**answered

You can calculate the pH of a buffer solution or the concentration of the acid and base using the Henderson Hasselbalch equation. Here's a look at the Henderson Hasselbalch equation and a worked example that explains how to apply the equation.Henderson-Hasselbalch Equation**pH = pKa + log ([A-]/[HA])**

[A-] = molar concentration of a conjugate base

[HA] = molar concentration of a undissociated weak acid (M)

The equation can be rewritten to solve for pOH:

**pOH = pKb + log ([HB+]/[ B ])**

[HB+] = molar concentration of the conjugate base (M)

[ B ] = molar concentration of a weak base (M)

Example Problem Applying the Henderson-Hasselbalch EquationCalculate the pH of a buffer solution made from 0.20 M HC2H3O2 and 0.50 M C2H3O2- that has an acid dissociation constant for HC2H3O2 of 1.8 x 10-5.Solve this problem by plugging the values into the Henderson-Hasselbalch equation for a weak acid and its conjugate base.

pH = pKa + log ([A-]/[HA])

pH = pKa + log ([C2H3O2-] / [HC2H3O2])

pH = -log (1.8 x 10-5) + log (0.50 M / 0.20 M)

pH = -log (1.8 x 10-5) + log (2.5)

pH = 4.7 + 0.40

pH = 5.1

Quite simple.