Question

the pH of the solution obtained by mixing 400ml 0.1M acetic acid, 50ml 0.1M sulphuric acid and 50ml 0.3m sodium acetate is (Ka of acetic acid is 1x10-5)

Answer 1

First, use the Henderson-Hasselbalch equation to determine the pH of the buffer portion of the system (acetic acid/sodium acetate). Then add in the H2SO4 which increases the concn of the acid and decreases the concn of the base (acetate). Re-solve for pH.