A buffer solution is a solution that maintains nearly constant pH despite the addition of small amounts of acid or base. That is because a buffer solution contains both a weak acid and its conjugate base. A relatively simple buffer system is one consisting of a mixture of acetic acid and its conjugate base, the acetate ion.
Many organic compounds show acidic or basic properties and some show both acid and base, which involve as intermediate in many multistep organic reactions in Organic Chemistry. The simplest type of buffer is composed of a weak acid-strong base combination or a weak base-strong acid combination.
Types of Buffer Solution
- Acidic Buffer – An acidic buffer maintains a solution at a pH below 7. It is a mixture of a weak acid and its conjugate base, for example ethanoic acid CH3COOH and sodium ethanoate, CH3COONa.
In this Buffer Solution there is
- A large amount of undissociated ethanoic acid, because it is a weak acid.
- A large amount of ethanoate ions owing to the addition of sodium ethanoate which completely ionises the solution.
- pH is maintained on either addition of small amount of acid or alkali.
- Basic Buffer – A basic buffer maintains a solution at a pH above 7. It is a mixture of a weak base and its conjugate acid, for example, ammonia NH3 and ammonium chloride, NH4Cl.
In this buffer solution, there is
- A large amount of undissociated ammonia, because it is weal base.
- A large amount of ammonium ions owing to the addition of ammonium chloride which completely ionises in solution.
What makes a Good Buffer?
In general, a good buffer includes comparatively equal levels of a weak acid and its conjugate base. For example, Haemoglobin is a good buffer due to its capacity to act as an oxygen acceptor as well as an oxygen donor.
Buffer solutions have two important properties. First, any aqueous solution of a desired pH using a weak acid and its conjugate base means a salt of the acid. The second property of buffer solution is that its pH will remain approximately constant if relatively small amounts of a further acid or base are added. This is very useful if a constant pH is required for a reaction which consumes or generates either H2O or OH-.
The concentration of the buffer system components will undergo change, but the expression governing the equilibrium will still be valid, and the pH will be maintained. Although buffer solutions will not maintain a fairly constant pH if large quantities of acids or bases are added to them, it is remarkable how much they can accommodate without an appreciable change in pH.