Look up the pKa values for H3PO4.
K1 = 7.1E-3 which makes pK1 = about 2
K2 = 6,3E-8 which makes pK2 = about 7
K3 = 4.5E-13which makes pK3 about 12. This one is within about 1 pH value of the desired pH of 11.8 and HPO4^- and PO4^3- are the acid/base pair respectively that you want to use.
First you solve two simultaneous equations.
Equation 1 is the Henderson-Hasselbalch equation which is
11.8 = pK3 + log (base/acid)
Solve for b/a.
Equation 2 is
b + a = 0.34M
So you now have concn of acid and concn of base.
Convert M concns to grams HPO4^- and grams PO4^3-.
POst your work if you get stuck.
calculate the mass of the species required to prepare a phosphoric acid buffer with a voncentration of 0.34M ,volume of 500ML and a PH of 11.8.calculate the mass of the varies species needed to prepare the buffer.salt of interest is sodium. consider the following information
H3PO4=H2PO4+H
H2PO4=HPO4+H
HPO4=PO4+H
1 answer
1 answer