A solution that resists change in pH when a small amount of a strong acid or a strong base is added to it is called a buffer solution.
Buffer action:- The resistance offered by a buffer solution to change in pH on the addition of acid or base is called buffer action.
Types of buffer solution
Pure water has a pH value equal to 7.0 but even the purest form of water cannot acidic this value for a very long time. The acorn is that carbon dioxide in the air dissolves in water and gives it a slightly acidic character. Thus buffer solution resists the change in pH.Â
For example
Blood is a buffer since it maintains a pH. of 7.4 under a wide range of physiological conditions.
Preparation buffer solutionÂ
A buffer solution is usually prepared from (i) Weak acids and its salts (ii) Weak base and its salts.
Acidic Buffer solution
A weak acid and its salts with a strong base like CH3COOH/CH3COONa make a solution called an acidic buffer. Acidic buffers have a pH of less than 7.0. Consider an acidic buffer solution consisting of acetic acid and sodium acetate when a strong base NaOH is added the added OH ions are removed by the reaction with acetic acid molecules.
CH3COOH + OH ⟶ CH3COO + H2O
When a strong acid is added H ion of the acid reacts with the acetate ion of the buffer.Â
H ion + CH3COO ion ⟶ CH3COOH
Both of these reactions go to completion hence the added OH ion and H ion are removed and the pH of the buffer solution remains constant.
Basic Buffer Solution
A weak base and its salt with a strong acid like NH4OH/NH4Cl make a solution called a basic buffer. The basic buffer solution pH is more than 7.0. Consider a basic buffer solution consisting of ammonium hydroxide and ammonium chloride on adding a strong acid such as HCl the added hydrogen ions are removed by reaction with NH4OH.
H ion + NH4OH ⟶ NH4 ion + H2O
Where the OH ions of the base added are removed by reaction with the ammonium ions of the buffer solution.
NH ion + OH ion ⟶ NH4OH
Determine the pH of the Buffer Solution
pH of the buffer solution is determined in two ways. (1) The value of Ka of a weak acid or Kb of the weak base.
(2) The ratio of the concentration of the weak acid and its conjugate base. The equation for the ionization of a weak acid is:
HA ⟶ H ion + A¯ ion
Ionization constant Ka of a weak acid is: Ka = [H+] [A¯] / [HA]
On rearranging [HA]Ka = [H+] [A¯]
[H+] = Ka [HA] / [A¯]
Taking -log on both sidesÂ
-log [H+] = -log ( Ka [HA] / [A¯]
-log [H+] = -log Ka - log [HA] / [A¯]
pH = PKa - log [HA] / [A¯]
pH = PKa + log [A¯] / [HA]
This equation is known as the Henderson-Hassel Balch equation.
Application and UsesÂ
1. The use of buffer solution is important in some industrial processes, where the process would be interrupted by a large change in pH. Such as the manufacture of leather, photographic materials, and dyes.
2. The bacteriological research culture media are generally buffered to maintain a constant pH required for the growth of the bacteria being studied.
3. Buffers are important in biological systems because the biochemical reactions in both plants and animals are often very sensitive to pH change Human blood is buffered to a pH of 7.4 by means of bicarbonate, phosphate, and complex protein system.Â
4. Many shampoos use a citric acid to maintain a slightly acidic pH balance
5. In the bearing industry, buffer solutions are added before fermentation begins.
6. Protein studies must be performed in buffered media because of the magnitude and kind of electrical charge.
Read Also Â
>Methods for determination of pH of water
>Preparation of Buffers, Indicators and Reagents
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