Buffers

• A buffer solution is one whose pH hardly changes when small quantities of acid or base are added
• How can an acid buffer be formed?

  An acid buffer consists of a weak acid and its conjugate base usually in form of one of its salts
• How can an alkaline/base buffer be formed?

  A basic buffer consists of a weak base and its conjugate acid
• Calculating pH of a buffer from weak acid + salt ?

  1. Use the Ka equation
  2. Rearrange equation to [H+]
  3. Then use pH equation
• When a small quantity of strong base is added to a excess of weak acid, a buffer solution is formed.

  • Some of the weak acid react with the strong base to form salt of weak acid
• Calculating pH of buffers formed from weak acids + strong base

  1. Write out the neutralisation equation
  2. Calculate number of moles of acid and base at the start of the equation
  3. Then using the balancing numbers calculate moles of salt using ratio. (base : salt )
  4. Work out the number of moles left of the excess weak acid
  5. Then calculate concentration of acid and salt
  6. Rearrange Ka equation to find [H+] and then use it to calculate pH