What are buffer solutions?

Buffer solutions are solutions comprised of a weak acid and it's conjugate base, or a weak base and its conjugate acid. The solutions are very resistant to change in pH when an acid or base is added.

An example of a buffer solution:

HF+H20 <--> H30+ + F-

*HF is the weak acid, F- is the conjugate base

-If acid (hydrogen ions, H+) were added to this solution, the H+ would react with the F- and would create more HF, shifting the equilibrium to the left. Consequently, there would be little change to the pH of the solution, as most of the H+ ions would be "used up". However, it is important to note that buffers do have a certain capacity, and once the acid is in excess (all of the F-(conjugate base) is converted back to HF), the solution will no longer be resistant to change in pH.

Buffers are substances that minimize changes in the concentrations of H⁺ and OH^- in a solution. Buffers do so by accepting hydrogen ions from the solution when they are in excess and donating hydrogen ions to the solution when they have been depleted.