Calculate the average net charge on phenylalanine if it is in a solution that has a ph of 8.70.

Phenylalanine has two known pKa charges: 1.83 and 9.13. To determine their individual ionic dissociation charges at pH 10, the equation to be used is

pH = pKa + log [α / (1-α) ]

At pKa 1.83:

10 = 1.83 + log [α₁ / (1-α₁) ]

α₁ = 0.99999

At pKa 9.13:

10 = 9.13 + log [α₂ / (1-α₂) ]

α₂ = 0.88114

Average Net Charge = 0.99999 + 0.88114 = 1.88