A buffer solution is a solution that has a tendency to resist changes in pH, even when an acid or base is added to the solution. Buffer solutions consist of a mixture of either a weak acid and its conjugate base, or a weak base and its conjugate acid, dissolved in water. When an acid is added, the base present in the solution tends to bind to the H+ from the acid, serving to “buffer” the change in pH and preventing the concentration of H3O+ from changing very much. Similarly, when a base is added, the acid in the solution tends to neutralize the base, again serving to buffer the change in pH by preventing the concentration of H3O+ from changing significantly.