Buffer Calculations

Key Questions

  • Buffer solutions are used to calibrate pH meters because they resist changes in pH.

    When you use a pH meter to measure pH, you want to be sure that if the meter says pH = 7.00, the pH really is 7.00.


    So you use solutions of known pH and adjust the meter to display those values.

    Buffers are ideal for this purpose because:

    • They are easily prepared for a given pH.
    • They are stable for long periods of time.
    • They resist changes in pH if you accidentally add a little acid or base or even water.


  • A buffer solution will maintain a constant pH with the addition of small amounts of acid and alkali.

    There is a limit to the amount of acid or alkali that the buffer can handle.

    The buffer capacity is given by the expression:


    #dn# is a tiny amount of added base which results in tiny change in pH shown as #d(pH)#

    If you have a weak acid whose dissociation constant is #K_a# then the buffer capacity is given by :

    upload.wikimedia.org (From Wiki)

    #C_A# is the concentration of the acid.