Buffer solutions:
A solution that resist the change in pH upon addition of small amount of a strong acid or a strong base is called a buffer solution. The capacity of a solution to resist alteration in its pH value is known as buffer capacity.
e.g. Ammonium acetate.
When a drop of HCL is added to a liter of pure water, the pH of the water changes immediately from 7 to about 2.2 Similarly, if a drop of NaOH solution is added to a liter of pure water, the pH of the water increases from 7 to about 12. The same type of changes occur for aqueous solution of NaCl. However, such change will not occur in some solutions like ammonium acetate. Even when 1 ml of acid or alkali is added to this solution, the pH of the solution will remain nearly 7.
The buffer solutions possess reserve acidity as well as reserve alkalinity.
Thus ammonium acetate has reserve acidity due to the presence of NH4 , ions and reserve alkalinity due to the presence of CH3COO- ions.
Any solution containing a weak acid together with one of its salt or a weak base with one of its salts, function as a buffer.
The buffer may be an acid buffer or a basic buffer. An acid buffer consist of a weak acid and its salt. e.g, CH3COOH+ CH3 COONA( Acetic acid+ sodium acetate).
A basic buffer is a mixture of a weak base and its salt
E.g, NH4OH+NH4CL.
A buffer can be represented by placing the acid or base as the numerator and their salts as the denominator.
Acid buffer= Acid/Salt
Basic buffer=Base/Salt
Examples for buffer
The following are the important buffers.
1. Acetate buffer=Acetic acid/Sodium acetate
2. Ammonium hydroxide buffer= Ammonium hydroxide/Ammonium chloride