Question

If you have 0.100 M Pyridine titrated with 0.100 M HCl, choose an appropriate indicator and explain?

Answer 1

Pyridine we will call Py
When we titrate this base, the equivalence point will occur when only the salt is present. It will hydrolyze. You can calculate the pH at that point.
PyH^+ + H2O ==> H3O^+ + Py

Ka for PyH^+ = (Kw/Kb) where Kw is 1 x 10^-14 and Kb is the ionization constant for pyridine. Set up an ICE chart, substitute into the Ka expression and solve for OH^-, then convert to pOH and finally to pH. The concn of the salt will be 0.05. I found the pH to be approximately 3.2 so you would want an indicator that would change at that point; i.e., 3.2 would be the middle of the range for the indicator.