Question: In a strong
acid solution, the amino acid histidine binds three protons. The acid
dissociation constants numbered from the weakest acid dissociation are 6.92 ×
10–10, 1.00 × 10–6 and 1.51 × 10–2 at 25°C. Calculate
the concentrations of the four forms of
histidine (His–, HisH, HisH2+and HisH32+)
in a 0.1 M solution of histidine at pH 7, assuming that these constants apply
at the ionic strength of the solution.
Solution:
