What is the role of fractional compositions in analytical chemistry?

How do you calculate the fraction of acid molecules in a solution using Ka and H+ concentration?

Using the Henderson-Hasselbalch equation, calculate the pH of a solution with a pKa of 4.75 and a ratio of conjugate base to weak acid of 10:1.

Which form predominates at a pH of 3 in a diprotic system with pKa1 = 2 and pKa2 = 5?

Given a solution with 0.1 M weak acid and 0.05 M conjugate base, calculate the formal concentration.