How do you determine ph when concentration of futylamine is equal to concentration of conjugate acid graphically?

Question

I have a titration curve, and I have the concentration for futylamine, but not the conjugate acid. I also have the molecular equation and net ionic one and an expression for ka, but I have no idea how to get pH from this. I don't have pKa. I need it to determine pKa.

Answer 1

When the [base] = [conjugate acid] the pH = pKa. You can see this in the Henderson Hasselbalch equation:

pH = pKa + log [conjugate base]/[acid] or pOH = pKb + log [conjugate acid]/[base]. When the concentrations are equal, the ratio is 1, and log of 1 = 0, so pH = pKa.

If you have the pH, then you also know the pKa and hence the Ka. Does this help?