Finding the initial pH of a titration using Henderson Hasslebach equation

In 1908, Lawrence Joseph Henderson derived an equation to calculate the pH of a buffer solution.[1] In 1917, Karl Albert Hasselbalch re-expressed that formula in logarithmic terms,[2] resulting in the Henderson–Hasselbalch equation.
Theory

A simple buffer solution consists of a solution of an acid and a salt of the conjugate base of the acid. For example, the acid may be acetic acid and the salt may be sodium acetate. The Henderson–Hasselbalch equation relates the pH of a solution containing a mixture of the two components to the acid dissociation constant, Ka, and the concentrations of the species in solution.[3] To derive the equation a number of simplifying assumptions have to be made. The mixture has the ability to resist changes in pH when a small amount of acid or base is added, which is the defining property of a buffer solution