pH of Polybasic acid buffers

pH of Polybasic acid buffers
Recall that for the 1:1 buffer, the pH .pK a
Example 1: Calculate the pH of the buffer solution made up to
be 0.10 M in H 2 NNH 2 and 0.10 M in H 2 NNH 3 Cl.
The two reactions associated with H 2 NNH 2 are:
H 2 NNH 2 + H 2 O º H 2 NNH 3 + + OH !
and H 2 NNH 3 + + H 2 O º H 3 NNH 3 2+ + OH !
Which one should be used?
Notice that H 2 NNH 2 and H 2 NNH 3 + are relevant.
Since this is a 1:1 buffer, one need only set the pOH to the
pK b
Kb1 = 1.2 × 10 –6
ˆ pOH = 5.92 Y pH = 8.08