Hi everyone,
I'm a doctor/programmer not a chemist and i'm stuck with a chemistry problem while trying to calculate the addition of CO
2, H
+, or HCO
3- to a simplified model of human blood (we can assume the blood is water)
I know that CO2 dissociates to carbonic acid then bicarbonate and hydrogen ions:
CO
2 + H
20
H
2CO
3 H
+ + HCO
3-which I can simplify:
CO
2 + H
20
H
+ + HCO
3-(I'm guessing we know the pKa for this)
I know that we can use a modified version of the henderson-hasselbach equation to then calculate [H
+] (and then pH of course)
[H
+] = k x PCO
2 / [HCO
3-]
If I ignore the effects of CO
2 binding to haemoglobin and amino groups, then adding CO
2 (or H
+ / HCO
3- etc.) to the blood should then allow me to calculate the change in pH according to the above equation.
The problem is that some of the CO
2 will dissociate to H
+ and HCO
3- according to the first equation, so before I calculate the pH I need to solve the math problem: Given that I know the starting concentrations of H
+, CO
2, and HCO
3-, can I calculate the new concentrations after addition of a know quantity of one of these chemicals?
This matters greatly when giving Na
+·HCO
3- to a patient. It produces large amounts of CO
2 which the patient then needs to exhale and can cause respiratory failure (so I need to be able to model this)
Please forgive me if I have made some elemental errors in chemistry understanding - it really isn't my knowledge base and I don't have access to a biochemist.
Kenneth