Chapter 16, Problem 16.83SP

Interpretation Introduction

Interpretation:

The $K_a$ of the amino acid serine should be calculated if it is $86.3\%$ dissociated at $pH=9.95$.

Concept introduction:

• For weak acids the dissociation can be explained by Arrhenius equation.
• According to Arrhenius equation the acid dissociation constant is given as:

  $K_a=\frac{{\alpha }^{2}c}{1-\alpha }$

$\text{Where}$$\text{α}$$\text{= degree of dissociation}$

$\text{c}$$\text{=molar concentration of the weak acid }$

• The molar concentration of the weak acid can be calculated from the $pH$of the weak acid.

Given:

Degree of dissociation, $\alpha$ = $86.3\%=0.863$

$pH$ of the weak acid, $pH=9.95$