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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.

From Chapter 10:

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10.11 : End Point Prediction: Gran Plot

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