Posted by kabelo on Tuesday, February 15, 2011 at 1:23pm.
I can't draw the titration curve for H3PO4 on this board but you can draw it on a piece of paper. You look at the curve and figure out what you have at certain points.
Beginning is H3PO4 and pH is about 1.5 or so for a 1 M solution of H3PO4.
First equivalence point is H2PO4^- and that occurs at pH = 1/2(pK1 + pK2) = about 4.5. So, between the beginning and the first equivalence the pH is somewhere between 1.5 or so and 4.5 and the species must be H3PO4 and H2PO4^-.
For different values of pH, it is done the same way. The pH at the second equivalence point is 1/2(pK2 + pK3) and at the third is approximately sqrt (KwK3/salt) = about 13 for a 1 M concn of the salt.
The equation for each equivalence point is
H3PO4 + OH^- ==> H2O + H2PO4^-
H2PO4^- + OH^- ==>H2O + HPO4^-2
HPO4^-2 + OH^- ==>H2O + PO4^-3
Related Questions
Chemistry - Phosphoric acid, H3PO4(aq), is a triprotic acid, meaning that one ...
chemistry buffers - What molar ratio of HPO4 2- to H2PO4 - in solution would ...
Chemistry - Phosphoric acid, H3PO4(aq), is a triprotic acid, meaning that one ...
Chemistry - Phosphoric acid, H3PO4(aq), is a triprotic acid, meaning that one ...
chemistry - write the formula of each acid and identify each as a diprotic, a ...
AP CHEMISTRY - Phosphoric acid is triprotic acid (three ionizable hydrogens). ...
chemistry - A 0.15M solution of weak triprotic acid is adjusted (base added) so ...
chemistry - A 0.15M solution of weak triprotic acid is adjusted (base added) so ...
Chemistry - Glutamic acid is triprotic amino acid with pKa values of 2.23, 4.42...
Chemistry - What is the volume of a solution of 0.5 M NaOH that must be added to...
For Further Reading
