Chapter 12, Problem 12.13P

Interpretation Introduction

Interpretation:

The titration results are should be reproduced by using spreadsheet equation for auxiliary complexing agent.

Concept introduction:

Spreadsheet equation for auxiliary complexing agent:

In the EDTA titration, the titration curve is drawn by a single equation, it is known as spreadsheet equation for auxiliary complexing agent and it applies whole titration because the reaction is carried out by at constant pH.

The spreadsheet equation for auxiliary complexing agent is,

$\varphi \text{=}\frac{{\text{C}}_{\text{EDTA}}{\text{V}}_{\text{EDTA}}}{{\text{C}}_{\text{M}}{\text{V}}_{\text{M}}}$

The spreadsheet equation for auxiliary complexing agent for ligand with metal is,

$\varphi \text{=}\frac{{\text{K}}_{\text{f}}{\text{''[M]}}_{\text{free}}\text{-}\frac{{\text{[M]}}_{\text{free}}{\text{+K}}_{\text{f}}{\text{''[M]}}^{\text{2}}{}_{\text{free}}}{{\text{C}}_{\text{L}}}}{{\text{1+K}}_{\text{f}}{\text{''[M]}}_{\text{free}}\text{+}\frac{{\text{[M]}}_{\text{free}}{\text{+K}}_{\text{f}}{\text{''[M]}}^{\text{2}}{}_{\text{free}}}{{\text{C}}_{\text{M}}}}$

Where,

${\text{K}}_{\text{f}}\text{''}$ is Conditional formation constant at constant pH with auxiliary complexing agent.

${\text{[M]}}_{\text{free}}$ is free metal ion  concentration

${\text{C}}_{\text{M}}$ is total concentration of metal ion

${\text{C}}_{\text{EDTA}}$ is concentration of metal EDTA

The titration curves and plot:

The observed values, which is recorded from the titration is plotted in a graph sheet is known as titration plot and the variation of plotted values result the curved graph line, the end point of the titration is determined from this graph line, where the maximum difference is results.