Question

How sodium carbonate and sodium bicarbonate act as buffer solution?

Answer 1

A classic buffer is a combination of a weak acid and its conjugate salt; for instance, carbonic acid (H2CO3)
and sodium bicarbonate (NaHCO3), or even sodium bicarbonate and calcium carbonate. What happens when
you titrate this combination with the (strong) acid of your choice? Well, in any buffer system, the boost in
[H+
] increases the reaction rate H+
+ salt => weak acid and takes some H+
out of circulation.
Of course, as it does so, it increases weak acid concentration, so the reverse reaction rate starts to increase
until you get a new equilibrium. Similarly, titration with a strong base decreases the H+
+ salt => weak acid
rate, and so (since the weak acid dissociation is still happening), the weak acid => H+
+ salt adds some H+
to
the solution. Thus the pH changes less than it would if you titrated pure water - it's buffered.