Chapter 18, Problem 111AE

Interpretation Introduction

Interpretation:

The pH of a sample of intercellular fluid containing a phosphate buffer with a concentration ratio of ${\text{H}}_{\text{2}}{\text{PO}}_4^{-}/{\text{HPO}}_4^{2-}$

as 1.1:1 needs to be deduced.

Concept Introduction:

A buffer is a solution of a weak acid (or base) and it’s salt. The main function of a buffer is to maintain the pH of a solution.

The pH of an acidic buffer (HA) is related to the acid dissociation constant Ka via the Henderson-Hasselbalch equation:

  $\begin{array}{l}\text{HA}\leftrightarrow {\text{H}}^{\text{+}}{\text{+A}}^{-}\\ {\text{pH = pK}}_{\text{a}}\text{ + log }\frac{{\text{[A}}^{-}\text{]}}{[\text{HA]}}\text{ ------ (1)}\\ {\text{pK}}_{\text{a}}\text{ = acid dissociation constant}\\ [{\text{A}}^{-}\text{] = concentration of the salt/conjugate base}\\ \text{[HA] = concentration of the acid}\end{array}$