Imagine a titration starting with 25 mL of 0.1 M phosphoric acid, and titrating it with 100 mL of 0.1 M KOH. Please go look up the Ka constants for phosphoric acid, and then,explain why I asked for so much more KOH than would be needed for CH3CO2H.
I can' tell how much of this is a question for the board and how much was the original question for you; however, the answer to your question is that H3PO4 is a triprotic acid and will require 3x as much titrant as will a monoprotic acid such as CH3COOH.
