Does anyone have a simple equation for generating curves that look
like titration curves?

They don't have to be accurate, just good enough to be able to teach
the common method used to estimate the pKa of a weak acid by titration
with an alkali.

G'day G'day Folks,

I've been called upon to coach some tertiary technician students
doing inorganic chemistry. When tutoring electrical theory I became
familiar with Graphmatica for drawing graphs representing things like
three phase etc. That was straight forward since the equations were
simple and easy to adjust by trial and error.

The curves that are produced when one titrates a weak acid with an
alkali produce curves that look similar to a sigmoid curve though not
so symmetrical.

Does anyone have a simple equation for generating curves that look
like titration curves?

They don't have to be accurate, just good enough to be able to teach
the common method used to estimate the pKa of a weak acid by titration
with an alkali.

Thank you.

Best wishes,

As a tutorial, I used the equation for buffer pH to set up
data in Excel to show how pH of the buffer decreases as acid
is added. I made a plot in Excel of the pH vs amount of
acid added, and showed the curve to a student., She
immediately connected it to a specific titration curve in
her textbook. I said, "You got it." The pH at the point of
maximum slope on that curve is a measure of pK.

I don't have the book handy, but the quantitative analysis textbook by
D.C. Harris has, among other things, a complete set of equations,
which you could plug into a spreadsheet. I now use this all the time,
whenever I need to simulate a titration curve.

As I recall, the simplest way to express the function was inverted -
it calculated volume added as a function of pH. So, it isn't a good
tool for telling you exactly the pH at zero added volume. However, it
reproduces the "sigmoidal" shape beautifully. If you set up the pKa
as an adjustable parameter in your spreadsheet, it becomes very easy
to crank out a variety of plots.

- Craig