The pH of human blood is steady at a value of approximately 7.4 owing to the following equilbrium reactions:
CO2(aq) + H2O(l) ⇌ H2CO3(aq) ⇌ HCO3-(aq) + H+(aq)
Acids formed during normal celluar respiration react with the HCO3- to form carbonic acid, which is in equilibrium with CO2(aq) and H2O(l). During vigorous exercise, a person’s H2CO3 blood levels were 26.3 mM, whereas his CO2 levels were 1.63 mM. On resting, the H2CO3 levels declined to 24.9. What was the CO2 blood level at rest?