What fraction of piperazine (perhydro-1,4-diazine) is in each of its three forms (H2A, HA–, A2–) at pH 8.67? The acid dissociation constant values for piperazine are Ka1 = 4.65×10–6 and Ka2 = 1.86×10–10.

Answer 1

You do these using the alpha system.
The denominator of the fraction is
D = (H^+)^2 + k1*(H^+) + k1k1

alphao = (H2A) = (H^+)^2/D
alpha1 = (HA^-) = k1*(H^+)/D
alpha2 = (A^2-) = k1k2/D
Plug in the numbers and solve.

Answer 2

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