Definition of Buffers
A solution which tends to resist changes in pH is called buffer solution. Buffer solutions are the solutions that resist changes in the concentration of hydronium ion and hydroxide ion (and therefore pH) when adding low amounts of acid or base, or when diluting the solution.
Regulated solutions are used to maintain pH at a constant degree in a large number of chemical applications. saline, a weak base, and salts are acid.
Importance of Buffers
In the human body, pH varies from liquid to liquid, for example, in the blood is 7.4, whereas, in the infectious juices 1.5, these values are considered appropriate and ideal for the work of enzymes and balancing Osmotic pressure.
These values are often maintained by structured solutions, and the most important solution is phosphate and bicarbonate.
Buffer Solution Capacity
Reflect the resistance of the regulated solution to the change in pH, and the largest possible when the ratio between the acid and the associated base is equal to one.
Examples: include acetic acid CH3COOH as a weak acid and its associated base is sodium acetate CH3COONa.
Preparation of Buffer Solution
A buffer solution of Acetic Acid and Sodium Acetate (Acidic Buffer)
Acetic acid dissociates to give acetate in a follows:
CH3COOH ======== CH3COO– + H+
Sodium acetate dissociates to give also acetate ions as follows:
CH3COONa ======== CH3COO– + Na+
When these two are mixed to make a buffer. There is an increase in the concentration of the acetate ions. Acetic acid equilibrium is pushed to left. So, H+ concentration is reduced and un-dissociated acetic acid is formed and there is no change in pH of the mixture.
how does the buffer solution works?
Case I: Study the effect of adding HCl to the solution:
1. Addition of HCl means the addition of H + and thus increasing the concentration of H3O + in the solution of the equilibrium Vichtel.
2. In accordance with the Leucatlier principle, the reaction (1) will be moved to the left by the excess H3O reaction with the CH3COO.
3. As a result of the displacement of the reaction (1) to the left, the effect of the increase in H3O concentration resulting from the addition of HCl will almost be eliminated and therefore the pH value of the solution remains almost constant.
Effect of Addition of Acid
In the case of added acid, additional H+ ions in the solution will combine acetate ions (CH3COO) to produce un-dissociated acetic acid and pH will remain the same.
CH3COO _ + H+ CH3COOH
Effect of Addition of Base
A small amount of base (NaOH) added to the buffer solution will be neutralized by the reaction will weak acid and pH will remain the same.
–OH + CH3COOH ======== CH3COO- + H2O
Applications of Buffer
- the use of the buffer is an important part of the many industrial processes, such as electroplating, manufacturing of the leather, etc.
- buffers are used extensively in analytical chemistry and are used to calibrate pH.
- Human blood is buffered to a pH of 7.3. by the means of bicarbonates, phosphates and complex protein system.