Chapter 9, Problem 9.4P

(a)

Interpretation Introduction

Interpretation:

In accordance to Henderson-Hasselbach equation $\text{pH}$ equal to $p{K}_a+2$ has to be shown.

Concept Introduction:

The equation for buffer is described by Henderson-Hasselbach equation and it is a rearranged for of equilibrium constant, $K_{\text{a}}$. Consider an equation of dissociation of an acid as follows:

  $\text{HA}\rightleftharpoons {\text{H}}^{+}+{\text{A}}^{-}$

Formula to calculate $\text{pH}$ is as follows:

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

Here,

$p{K}_{\text{a}}$ is acid dissociation constant of weak acid $\text{HA}$.

$\left[{\text{A}}^{-}\right]$ is concentration of conjugate base ${\text{A}}^{-}$

$\left[\text{HA}\right]$ is concentration of acid $\text{HA}$.

(b)

Interpretation Introduction

Interpretation:

In accordance to Henderson-Hasselbach equation $\text{pH}$ is equal to $p{K}_a-3$ value of $\frac{\left[{\text{A}}^{-}\right]}{\left[\text{HA}\right]}$ has to be calculated.

Concept Introduction:

Refer to part (a).

(c)

Interpretation Introduction

Interpretation:

In accordance to Henderson-Hasselbach equation if value of $\frac{\left[{\text{A}}^{-}\right]}{\left[\text{HA}\right]}$ is ${10}^{-4}$ then $\text{pH}$ has to be calculated.

Concept Introduction:

Refer to part (a).