Question

In the blood plasma, pH is maintained by the carbonic acid-bicarbonate buffer system. Explain how pH is maintained when (a) acid is added to the buffer system, (b) base is added to the buffer system?

Answer 1

Buffer mixture resists the change in pH on addind acid or base over a period of range.

Its pH remains same if we add either acid or base.

The buffer system present in blood plasma is

H₂CO₃ + HCO₃^-               [Weak acid + salt of the weak acid.]

When an acid is added to this buffer:

example take HCl: [hydrochloric acid]

HCl reacts with the salt present in the buffer system as shown below:

HCl + HCO3- -----------------> Cl- + H2CO3

So the weak acid is formed again and its dissociation decreases further due to common ion effect and there will be no change in pH of the solution.

Addition of base:

for example add: NaOH

NaOH reacts with the weak acid present in the buffer solution. The reaction is as shown below:

NaOH + H₂CO₃ ---------------------> NaHCO3 + H2O

Again the conjugate base of the weak acid along with water is formed.

Hence there is no change in pH of the solution.