Strong acids and bases ionize completely in aqueous solutions. Weak acids and bases ionize only partially in aqueous solutions. An acid-base reaction is shown below. A titration was done by adding a base to a known concentration and fixed volume of an acid. The reaction follows:
The dissociation of a weak acid can be represented as:
Chemists often use Henderson-Hasselbach equation to calculate the pH of solutions containing a weak acid of known pKa, provided that the other concentrations are known. Henderson-Hasselbach equation is:
This equation is also used to calculate the buffering capability of solutions. It is roughly estimated that a given buffer is most likely to be effective at pH levels between (pKa + 1) and (pKa – 1).
What is the pH of a 3.2 x 10–4M solution of HCl?