Titration curve

Titrations are often recorded on graphs called titration curves, which generally contain the volume of the titrant as the independent variable and the pH of the solution as the dependent variable (because it changes depending on the composition of the two solutions).

[1] The equivalence point on the graph is where all of the starting solution (usually an acid) has been neutralized by the titrant (usually a base).

It can be calculated precisely by finding the second derivative of the titration curve and computing the points of inflection (where the graph changes concavity); however, in most cases, simple visual inspection of the curve will suffice.

To calculate the logarithmic acid dissociation constant (pKa), one must find the volume at the half-equivalence point, that is where half the amount of titrant has been added to form the next compound (here, sodium hydrogen oxalate, then disodium oxalate).

Therefore, the Henderson-Hasselbalch equation can be solved in this manner: Therefore, one can easily find the pKa of the weak monoprotic acid by finding the pH of the point halfway between the beginning of the curve and the equivalence point, and solving the simplified equation.