Chapter 13, Problem 146AE

The pH of human blood is steady at a value of approximately 7.4 owing to the following equilibrium reactions:

${\text{CO}}_{\text{2}}\left(aq\right)+{\text{H}}_{\text{2}}\text{O}\left(l\right)\rightleftharpoons {\text{H}}_{\text{2}}{\text{CO}}_3\left(aq\right)\rightleftharpoons {\text{H}}_{\text{2}}{\text{CO}}_3{}^{-}\left(aq\right)+{\text{H}}^{+}\left(aq\right)$

Acids formed during normal cellular 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 mM. What was the CO₂ blood level at rest?