[student12393]

So the question is as follows:

A hypothetical protein with a single ionizable functional group takes on a charge of -1 when deprotonated. Find the equation for the average charge Z on the molecules as a function of pH and pKA of this functional ionizable group.

So the only equation I know of in regards to charge "Z" is the the Ionic Strength formula which is I = 1/2 Σ(i) ciZi^2. I'm not sure how to relate this at all with pH or pKA, and have had no luck when trying to come with something using the Henderson–Hasselbalch equation.