A buffer is a mixture of a weak acid and its conjugate base or a weak base and its conjugate acid; such mixtures are effective in resisting change in pH when strong base or acid is added to a solution. By definition a weak acid or a weak base is one that only slightly dissociates when dissolved in water. Acetic acid is a weak acid whose behavior can be described by the following equilibrium expression and acid dissociation constant.
If one mole of acetic acid is added to water with a final volume of 1 Liter,
then only about 0.4% of the acid is dissociated. If a strong base is added
to a weak acid, the acid dissociates, releasing a proton
If 0.010 moles of NaOH (a strong base) are added to pure water (final volume 1 Liter), the pH of the solution will be 12. On the other hand, if 0.010 moles of NaOH are added to a solution of 0.010 M acetic acid (final volume 1 Liter), the pH increases from 3.2 to 4.76, according to the Henderson-Hasselbalch equation.
To prepare a 0.010M sodium acetate buffer, pH 4.76, you need to add NaOH
to a concentration of 0.010 M to a 0.010 M acetic acid solution. This is
normally done by adding 0.010 moles of acetic acid to 900 mL of water, then
adding 0.010 moles of NaOH gradually while checking the pH with a pH meter.
The solution is then brought to a final volume of 1 Liter in a volumetric
flask. It is important to check the pH with a calibrated meter because
A plot of pH vs. equivalents of NaOH added to a solution of acetic acid
shows that it is most effective in buffering when the pH is close to the
Although this application offers a choice of only three buffers, other
buffers with a wide range of