posted by lucia on .
why is a weak acid weak base titration different from strong acid strong base/ weak acid strong base/strong acid weak base?
Any combination of acid and base titration will give a SHARP end point caused by a large increase (or decrease depending upon what is titrating what) of about 4 or 5 pH units EXCEPT for the titration of a weak acid with a weak base. With the WA/WB titration it is essentially impossible to determine where the inflection point(the equivalence point) is located. Color indicator rely on a color change over a pH range of two (2) pH units and that occurs with just a drop of titrant. With a WA/WB titration, one drop causes no such color change because the increase in pH is not noticeably different. Look in your text for the titration curves and you can see what I'm talking about. Or go to google and type in pictures of titration curves. Perhaps I can find one on the web if yu can't find one. We can't draw them on this board.
so then for a weak acid weak base titration indicators don't work?
That's right. They (color indicators) don't work for WA/WB titrations.