pH and Buffers Defined
pH is a measure of the concentration of H+ [H3O+] ions in a solution. Only the concentration of H+ and OH- molecules determine the pH. When the concentration of H+ and OH- ions are equal, the solution is said to be neutral. If there are more H+ than OH- molecules the solution is acidic, and if there are more OH- than H+ molecules, the solution is basic.
To be able to add a strong acid or base to a solution without causing a large change in the pH, we need to create a buffer solution. A buffer solution contains both a weak acid (HA) and its conjugate base (A-).