A Gran plot is used to predict the equivalence volume or endpoint of a potentiometric or acid-base titration without reaching the endpoint. Typically, titration data is collected as a function of the titrant's volume up to a point less than the equivalence volume and then transformed into a linear format. The straight line is extended to the x-axis, indicating the necessary titrant volume to achieve the equivalence point.
For potentiometric titration, the Gran plot is created by plotting the volume-corrected base-10 antilogarithm of the measured electrode potential (E) against the titrant volume. The equivalence volume can be predicted by fitting the best line through the data points and extrapolating back to the x-axis. Likewise, using the Gran plot equation for a weak acid-strong base titration produces a straight line, where the slope of the line is equal to the negative activity-corrected acid dissociation constant, and the x-intercept corresponds to the titrant volume at the endpoint.
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.
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