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) [bicarbonate]/[carbonic acid] = 0.11D) [bicarbonate]/[carbonic acid] = 9.4B) [bicarbonate]/[carbonic acid] = 0.38E) None of the above ratios is correct.C) [bicarbonate]/[carbonic acid] = 2.65

Answer 1

Answer: Option (B) is the correct answer.

Explanation:

The given data is as follows.

         pH for blood = 7.35,                    

     For carbonic acid, $K_{a_{1}} = 4.2 \times 10^{-7}$

Therefore, calculate the pH of buffer solution as follows.

    pH = $pK_{a_{1}} + log \frac{\text{Conjugate anion}}{\text{Acid}}$

          = $-log K_{a_{1}} + log \frac{\text{bicarbonate}}{\text{carbonic acid}}$

Now, putting the given values into the above formula as follows.

      pH = $-log K_{a_{1}} + log \frac{\text{bicarbonate}}{\text{carbonic acid}}$

        7.35 = $-log (4.2 \times 10^{-7}) + log \frac{\text{bicarbonate}}{\text{carbonic acid}}$

         7.35 = $6.377 + log \frac{\text{bicarbonate}}{\text{carbonic acid}}$

       $\frac{\text{bicarbonate}}{\text{carbonic acid}} = 10^{0.937}$

                                       = 9.4

Therefore, we can conclude that the ratio of [bicarbonate]/[carbonic acid] at this pH is 9.4.