Chapter 16.5, Problem 3PE

Interpretation Introduction

Interpretation:

The concentrations of ${\text{H}}_{\text{2}}{\text{C}}_{\text{2}}{\text{O}}_{\text{4}}\text{,}{\text{HC}}_{\text{2}}{\text{O}}_{\text{4}}^{\text{-}}\text{,}{\text{C}}_{\text{2}}{\text{O}}_{\text{4}}^{\text{2-}}\text{and}{\text{H}}^{\text{+}}$ ions in the given concentration of oxalic acid have to be calculated.

Concept Introduction:

Oxalic acid is a diprotic acid which means it consists of two protons.

In the first dissociation, one proton will be lost and the corresponding conjugate base will be formed.

In the second dissociation, the conjugate base of the 1^st dissociation acts an acid which further losses the 2^nd proton and forms its corresponding conjugate base.

The dissociation reactions of oxalic acid are:

  $\begin{array}{l}\text{1st}\text{dissociation}\\ {\text{H}}_{\text{2}}{\text{C}}_{\text{2}}{\text{O}}_{\text{4}}\stackrel{}{\rightleftharpoons }{\text{HC}}_{\text{2}}{\text{O}}_{\text{4}}^{\text{-}}\text{+}{\text{H}}^{\text{+}}{\text{K}}_{\text{a}}\text{=}5.6\times {10}^{-2}\\ \text{2nd}\text{dissociation}\\ {\text{HC}}_{\text{2}}{\text{O}}_{\text{4}}^{\text{-}}\stackrel{}{\rightleftharpoons }{\text{C}}_{\text{2}}{\text{O}}_{\text{4}}^{\text{2-}}\text{+}{\text{H}}^{\text{+}}{\text{K}}_{\text{a}}\text{=}5.1\times {10}^{-5}\end{array}$

The concentration of the given ions can be calculated using two ICE tables, each one corresponding to one of the two dissociations of the diprotic oxalic acid.

The model for an ICE table is shown below:

The equation is:                                      $\text{A}$            $+$          $\text{B}$        $\stackrel{}{\rightleftharpoons }$      $\text{AB}$
$\begin{array}{l}\text{Initial}\text{Concentration}\\ \left(\text{in}\text{mol/M}\right)\end{array}$	Some value	Some value	0
$\begin{array}{l}\text{Change}\text{in}\text{Concentration}\\ \left(\text{in}\text{mol/M}\right)\end{array}$	-x	-x	+x
$\begin{array}{l}\text{Concentration at equilibrium}\\ \left(\text{in}\text{mol/M}\right)\end{array}$	Some value -x	Some value -x	0 +x

Where,

1. A- Reactant
2. B- Another Reactant

  AB- Product.

  x- change in the concentration.

The -ve sign of x represents the decrease in the concentration whereas +ve sign of x represents the increase in the concentration.