Chapter 19, Problem 19.11P

Interpretation Introduction

Interpretation:

Scatchard plot has to be prepared and value of K along with the fraction of saturation for the data has to be given.

Concept Introduction:

Scatchard plot:

The equilibrium constant can be measured by measuring the concentration of the species at equilibrium.

Consider, a species P reacting with ligand X to form PX

$\text{P+X}\stackrel{}{\rightleftarrows }\text{PX}$

Neglect the activity coefficients, we get,

$\text{K=}\frac{\left[\text{PX}\right]}{\left[\text{P}\right]\left[\text{X}\right]}$

Suppose a series of solutions increments of X are added to a constant volume of P.

Let ${\text{P}}_{\text{0}}$ be total concentration of P,

$\left[\text{P}\right]{\text{=P}}_{\text{0}}\text{+}\left[\text{PX}\right]$

The expression for equilibrium can be rearranged as below,

$\frac{\left[\text{PX}\right]}{\left[\text{X}\right]}\text{=K}\left[\text{P}\right]\text{=K}\left({\text{P}}_{\text{0}}\text{-}\left[\text{PX}\right]\right)$

A graph of $\left[\text{PX}\right]\text{/}\left[\text{X}\right]$ versus $\left[\text{X}\right]$ along with slope of –K is called Scatchard plot.

Figure 1

To prepare Scatchard plot

To calculate the value of K along with the fraction of saturation