Question

The pH of blood is 7.35. It is maintained in part by the buffer system composed of carbonic acid (H2CO3) and the bicarbonate (hydrogen carbonate, HCO3-) ion.What is the ratio of [bicarbonate]/[carbonic acid] at this pH? For carbonic acid, Ka1 = 4.2 10-7.a) [bicarbonae]/[carbonic acid] = 0.11.b) [bicarbonate]/[carbonic acid] = 9.4.c) [bicarbonate]/[carbonic acid] = 0.38.d) None of the above ratios is correct.e) [bicarbonate]/[carbonic acid] = 2.65.

Answer 1

Answer:

b) [bicarbonate]/[carbonic acid] = 9.4

Explanation:

The pH of a buffer system is given by the Henderson-Hasselbach equation:

• pH = pKa + log ([bicarbonate] / [carbonic acid])

Where pka = -log (Ka) = -log(4.2x10⁻⁷) = 6.38

Now we solve for [bicarbonate] / [carbonic acid]:

• 7.35 = 6.38 + log ([bicarbonate] / [carbonic acid])

• 0.97 = log ([bicarbonate] / [carbonic acid])

• $10^{0.97}$ = [bicarbonate] / [carbonic acid]

• [bicarbonate] / [carbonic acid] = 9.33 ≈ 9.4

So the answer is b).