Question

Some friends and I were working on this problem and we think we got through A. and B. but we're having a hard time figuring out C.

5)

a) What is the ratio of bicarbonate (HCO3 -) to carbonic acid (H2CO3) in blood at its normal pH of 7.4?  Ka for carbonic acid is 4.3 x 10-7.

b)  After heavy exercise, an athleteʹs blood pH was detemined to be 7.1.  What is the ratio of bicarbonate (HCO3 -) to carbonic acid (H2CO3) at that pH of 7.1?

c)  During recuperation, the athleteʹs blood pH returns to normal as the excess carbonic acid is ʺblown offʺ as CO2.  If we assume that the bicarbonate concentration was a constant 0.024 M, and the athlete had a blood volume of 5 liters, what volume of carbon dioxide (at 1 atmosphere and 37 °C) must be expired?

Answer 1

this is a equilibrium problem, first you need your reaction and your mass action equation:

A) for this one you just need the ratio of the two species, you need to arrange the equation as follows:

B)Same as above, but now at pH= 7.1

C) If you have a constant concentration of HCO3 you can calculate the concentration of H2CO3 at both pH's.

at pH=7.4

at pH=7.1

when the athlete is recovering, he is loosing is the difference of H2CO3 at pH=7.1 minus the H2CO3 at pH=7.4

From the reaction:

You can assume that all the H2CO3 is lost as CO2

You can calculate the moles of CO2 lost using the volume:

using the ideal gas equation you can calculate the volume of CO2 expired:

at 1 atm, 310K, R=0.08206L atmK^-1mol^-1