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How to use graphical analysis in Windows to study titration curves of weak acid solutions using the example of NaOH titration. It covers the process of obtaining a better approximation of the equivalence point volume by creating a first derivative plot, which shows the change in slope of the titration curve as a function of the added volume of base. step-by-step instructions on how to create a first derivative column and plot it alongside the original titration curve.
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Using Graphical Analysis in Titration Curves
A typical titration curve obtained by plotting the measured pH of a weak acid solution as a strong base is added using graphical analysis for Windows is illustrated as follows:
The equivalence point is halfway up the vertical portion of the curve, about 27 mL for this titration. The pH is about 9 at the equivalence point.
To obtain a better approximation of the volume at the equivalence point, one can do a first derivative plot. This plots the change of pH divided by the change in volume versus the volume of NaOH. This shows the change in slope of the titration curve as a function of the added volume of base.
On the main graphical analysis screen: click on the data icon , the new column field , and the calculated field. The screen will be as follows.
Type in First Derivative for the new column name. Click in the New Column Formula box to place the cursor there. Then click on Other Functions. The screen will be as follows.
In the Other Functions box, click on the derivative () option, and then click on the Columns box. The screen will be as follows.
The following graph will appear.
The peak at around 27 mL is the equivalence point of the titration.
By clicking on the pH label on the vertical axis and clicking on both the pH and first derivative options in the y-axis setup box , one display both the first derivative and titration plots on one graph as follows.
