Chapter 15, Problem 15.131CHP

Interpretation Introduction

Interpretation:

The molar mass, $p{K}_{a1}andp{K}_{a2}$ of the acid has to be determined.

Concept Introduction:

Molarity: The concentration for solutions is expressed in terms of molarity as follows,

$\text{Molarity = }\frac{\text{No}\text{. of moles of solute}}{\text{Volume of solution in L}}$

Important formulas regarding acid-base concepts are:

$\begin{array}{c}\text{pH}\text{=}\text{-}\text{log}\left({\text{H}}^{\text{+}}\right)\\ \text{pOH}\text{=}\text{-}\text{log}\left({}^{\text{-}}\text{OH}\right)\\ \text{pH}\text{+}\text{pOH}\text{=}\text{14}\\ \text{pKa}\text{=}\text{-}\text{log}\text{Ka}\end{array}$

Acid dissociation constant:

Consider a weak-acid equilibrium reaction,

$\text{HA}\stackrel{{\text{K}}_{\text{a}}}{\rightleftharpoons }{\text{H}}^{\text{+}}{\text{+A}}^{\text{-}}$

The acid dissociation constant ${\text{K}}_{\text{a}}$ can be given as,

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

A weak acid is one that doesn’t undergo completion.

The negative logarithm of equilibrium constant is called as $\text{pK}$

The ${\text{pK}}_{\text{a}}$ of weak acid is the negative logarithm of ${\text{K}}_{\text{a}}$ and can be given as,

${\text{pK}}_{\text{a}}\text{=-log}{\text{K}}_{\text{a}}$

The value of acid dissociation constant ${\text{K}}_{\text{a}}$ decreases with increase in ${\text{pK}}_{\text{a}}$