Question

Use Henderson-Hassalbach equation. The pKa of Tris-HCl is 8.1. After you have added 1N HCl to adjust the pH of the Tris solution to 8.1 what is the ratio (in mmols) of Tris to Tris-HCl in the resulting buffer solution?

Answer 1

Explanation:

According to the Henderson-Hassalbach equation for pH is as follows.

        pH = $pK_{a} + log \frac{\text{conjugate base}}{acid}$

It is given that the pH and $pK_{a}$ are same.

Hence,    $pH - pK_{a} = log \frac{\text{conjugate base}}{acid}$

       $log \frac{\text{conjugate base}}{acid}$ = 0

      $\frac{\text{conjugate base}}{acid}$ = $10^{0}$

                                 = 1

Hence, whenever the pH and $pK_{a}$ are same then the ratio of conjugate base to acid is 1.

Thus, we can conclude that the ratio of Tris to Tris-HCl is 1.