21.1 Buffer solutions

• Buffer solutions are used to minimise changes in pH to a solution on addition of small amounts of an acid or base
• Acid buffer solutions contain two components, a weak acid and its conjugate base
• There are two methods to produce a buffer solution

  • solution of weak acid and a salt of that weak acid
  • excess solution of weak acid and an alkali

  Each method produces a buffer solution that contains

  • a large concentration of the weak acid
  • a large concentration of the conjugate base
• The control of pH by a buffer solution can be explained in terms of equilibrium shifts

  • added acid reacts with the conjugate base, shifting equilibrium to the left
  • added alkali reacts with H+ to form water, shifting equilibrium to the right
• Calculating the pH of buffer solutions

  [H+] = Ka x [HA]/[A-]