10.11 : End Point Prediction: Gran Plot

A Gran plot can predict a potentiometric or acid–base titration's equivalence volume or end point without actually titrating to the end point.

The usual titration data that tracks the progress of the titration reaction as a function of the titrant's volume is collected up to a volume less than the equivalence volume and is then converted into a linear form.

After linear regression, the straight line is linearly extrapolated to the x-axis, giving the titrant volume required to reach the equivalence point.

The Gran plot for potentiometric titration is obtained by plotting the volume-corrected base-10 antilogarithm of electrode potential against the titrant volume.

Fitting the best line through the data points and extrapolating to the x-axis predicts the equivalence volume.

Similarly, a weak acid–strong base titration using the Gran plot equation results in a straight line with a slope of the negative activity-corrected acid dissociation constant and an x-intercept equal to the titrant volume at the end point.