The ratio of [HCO3-] / [H2CO3] in the blood is 20:1, pH is 7.4. How did it come up with that ratio?

Question

What formula was used. Pls explain to me how to get the ratio...

Answer 1

For most buffers the Henderson-Hasselbach equation is used.
pH = pKa + log(anion/acid). In this case the pKa of carbonic acid is 6.1 leaving the log (anion/acid) to be 1.3. (7.4-6.1). Next take that difference and make it a power of 10. 10^1.3 = 20 or very close to that. Actually a bit less than 20 but close enough for this level of significance. Try that on your scientific calculator for verification.