Question

Orthophosphate (PO4 3- ) is a soluble polyprotic acid capable of protonating/deprotonating up to 3 protons to produce aqueous H3PO4 0 , H2PO4 - , HPO4 2- and PO4 3- . The pKa values of the associated dissociation reactions are as follows: pKa1=2.1; pKa2 = 7.2; and pKa3 = 12.4. Here you are asked to construct the speciation diagram of orthophosphate showing the concentrations of each of the four orthophosphate species in the pH range 1 -14 for a solution with a total orthophosphate concentration of 0.005 M (i.e. 5 mM). To this end, derive the equations that describe the concentration of each species as a function of pH. You can assume that concentration = activity (i.e. no need for activity corrections).

Answer 1