Question

The concentration of H3O+ in our blood must be maintained at a relatively constant value so that the pH stays at about 7.4. An increase in H3O+ will lower the pH, and a decrease in H3O+ will raise the blood pH. Death can result if the pH falls below 6.8 or rises above 7.8.

Explain, in terms of Le Chatelier’s principle, how this set of equilibria involving a buffer system prevents large changes in pH (or H3O+ concentration).

Answer 1

In blood,

CO2 + H2O <==> H2CO3

which dissociates as,

H2CO3 + H2O <==> H3O+ + HCO3-

A buffer exists between [H2CO3] <==> [HCO3-]

If an acid is added, the concentration of H3O+ on product side would rise, and thus equilibrium will shift towards right handside. This is by following LeChatellier's principle.

If a base is added, it would react with the H2CO3 in solution to form more of H3O+ and HCO3-. Thus according to LeChatellier's principle, equilibrium will shift towards left handside.