Posted by eric on .
A 0.1 M solution of acetic acid is titrated with 0.05M solution of NaOH. What is the pH when 60% of the acid has been neutralized? The equilibrium constant (Ka) for acetic acid is 1.8x10^5

chemistry 
DrBob222,
You can do this one of two ways, both using the HendersonHasselbalch equation.
pH = pKa + log(base)/(acid).
You CAN simply substitute 60 for base and 40 for acid and solve OR, if that is a little confusing, you can assume some convenient volume of acetic acid (say 50 mL or something like that), neutralize 60% of that, calculate base concn and acid concn and substitute. The fraction will always turn out to be 6/4 for the 60/40 ratio.