Chapter 8, Problem 8.72P

Interpretation Introduction

Interpretation:

If a HEPES buffer at pH 4.75 is usable buffer or not should be explained.

Concept Introduction:

The buffer consists of zwitter ions molecules which have both positive and negative charges. They are concentration and temperature change resistant. To understand the buffer it is not important to know its structure only the $\text{p}{K}_{\text{a}}$ values of the buffer and the needed concentration are enough to calculate its pH using Handerson-Hasselbalch equation which is as follows:

$\text{pH}=\text{p}{K}_{\text{a}}+\log \frac{\left[{\text{A}}^{-}\right]}{\left[\text{HA}\right]}$

Here, pH is negative log of hydrogen ion, $\text{p}{K}_{\text{a}}$ is negative log of acid dissociation constant, $\left[{\text{A}}^{-}\right]$ is concentration of conjugate base and $\left[\text{HA}\right]$ is concentration of acid.