Calculate the quotient [H3PO4]/[H2PO4] in 0.05 M K2HPO4. K1= 7.11x10^-3, K2= 6.32x10^-8, K3=4.17x10^-3
HPO42- ---------------> H+ + PO43-
0.05 0 0
0.05 - x x x
ka3 = x^2 / 0.05 - x
4.17 x 10^-13 = x^2 / 0.05 - x
x = 1.44 x 10^-7
[H+] = 1.44 x 10^-7 M
H3PO4 -------------> H+ + H2PO4-
Ka1 = [H+][H2PO4-] / [H3PO4]
7.11 x 10^-3 = [H2PO4-] x 1.44 x 10^-7 / [H3PO4]
[H2PO4-] / [H3PO4] = 49241.6
[H3PO4] / [H2PO4-] = 2.03 x 10^-5
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