What is the pH of a solution made by mixing equal vlumes of .10 M HC2H3O2, .1 M NaOH, and .05 M HCl?
Suppose you make up some numbers.
100 mL HAc x 0.1M = 10 mmols HAc.
100 mL HCl x 0.05 = 5 mmols HCl AS IONS.
Adding 100 mL x 0.1M NaOH AS IONS I think will react predominately with the HCl leaving 10 mmols HAc and 5 mmols NaOH. That will produce 5 mmols NaAc and leave 5 mmols HAc un-reacted. That makes a buffer solution. I would use the Henderson-Hasselbalch equation to calculate pH.
I think the answer will be 4.74 or very near that. It depends upon what you use for Ka HAc.