In article
>,
Madalch > wrote:

> On Dec 20 2009, 7:02*pm, "Paul E. Lehmann" >
> wrote:
> > No don't abandon the test. *It is really quite easy if you have a pH meter.
> > The color change occurs when the pH reaches 8.2. *Simpley add the NaOH as
> > you normally do and at the same time stir and watch your pH. *The end point
> > occurs when the pH is 8.2. *I know, it is not real intuitive that 8.2 is
> > the end point instead of 7.0 but 8.2 is the point at which the indicator
> > indicates neutrality
>
> It's not 7 because you're neutralizing weak acids (acetic, tartaric,
> etc) with a strong base.

It's the isoelectric point of tartaric acid, where it isn't an ion, but
still has both of its "acidic" protons attached.

http://en.wikipedia.org/wiki/Isoelectric_point
--
³When you give food to the poor, they call you a saint. When you ask why the poor have no food, they call you a communist.²
-Archbishop Helder Camara

http://www.jpost.com/servlet/Satelli...cle%2FShowFull
http://countercurrents.org/roberts020709.htm