• The term buffer is used in a lot of ways. In general usage, it suggests a cushion or barrier of some kind between two zones. Chemically, the meaning is analogous.
  • In chemistry, a buffer is a solution that resists a change in pH. So, it sort of “cushions” a solution against large or rapid variations in acidity or basicity.
  • A well buffered solution can take a reasonable addition of strong acid or base, and react in such a way as to take H+ or OH- ions out of solution, thus keeping the acid-base balance relatively stable.
  • Buffers themselves can either be acidic (pH < 7) or basic (pH > 7).
  • Buffers are made by combining a weak acid in solution with its conjugate (weak) base.
  • A generic acid, HA has a conjugate base of A-, where H is a proton to be released as H+ (that makes it an acid) and A- is a counter ion (which could be a lot of things).
  • An example: Phosphoric acid (H3PO4) is a weak acid where there are three possible H+ ions to be released (the H part) and the PO4-3 (that’s the A- part). If we combine it in solution with sodium phosphate (Na3PO4) we provide some sodium ions and more of the phosphate PO4-3 (that’s the conjugate base).
  • In the above example, only a little of the H3PO4 ionizes (because it is a weak acid) and much of the H3PO4 remains un-ionized in solution.
  • If a strong acid is added to this solution, it will preferentially react with the free PO4-3 (mostly from the Na3PO4) rather than water to make more of the weak acid H3PO4 instead of H3O+ so the pH doesn’t change much at all.
  • If a bit of strong base (OH-) is added to the solution, the weak acid (H3PO4) will release one of it’s protons to combine with the OH- to create water (H2O) and again the pH doesn’t change much at all.