Polyprotic Equations Slide
Polyprotic Acid-Base Equations
![](Polyprotic01.gif)
![](Polyprotic02.gif)
![](Polyprotic03.gif)
After plugging these terms into a proper charge balance equation we
can produce an advanced solution to any acid-base problem.
For quick and dirty pH calculations for most points in the
polyprotic titration curve, we can divide the curve into the following
regions:
![](Polyprotic04.gif)
At 0 mL HCl added, we have a solution of pure
Na2CO3. Try treating this as a monoprotic weak base,
where Kb = Kw/K2
Between 5 mL and 15 mL we are in one of the buffer regions. Here
![](Polyprotic05.gif)
At 20 mL HCl, we have the first end point, and a solution of pure
NaHCO3 in water, an amphiprotic substance.
![](Polyprotic06.gif)
From 25 to 35 mL we have the other buffer region. Here
![](Polyprotic07.gif)
At 40 mL HCl added, we have the equivalent of pure
H2CO3. Try treating this as a monoprotic weak acid
where Ka = K1.
David L. Zellmer, Department of Chemistry, California State University, Fresno. March 17, 1997