Question

Human blood is kept at a typical pH of 7.40 mainly by the carbonic acid–carbonate ion buffer system. The corresponding chemical equation describing the buffer would be: H2CO3(aq) + H2O(l) ⇌ HCO3-(aq) + H3O+(aq) The appropriate Ka value for carbonic acid is 4.3×10-7, so its pKa value is 6.37. Calculate the [base]/[acid] ratio in human blood. (Answer to 3 significant figures, no units)

Answer 1

According to the equilibrium reaction given for the buffer system in human blood:

The equilibrium constant for this reaction is:

Taking logarithms in equation (1):

Rearranging this equation according from the logarithmic properties:

Multiplying this equation by -1:

According to the definition of pH and pKa:

The ratio [HCO₃^-]/[H₂CO₃] is then:

Substituting known values: