On Jan 11, 12:10*pm, Wildbilly > wrote:
> In article
> >,
>
> *Madalch > wrote:
> > 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.

No it isn't. Tartaric acid will have both of its acidic protons
attached at a low pH; when you react it with sodium hydroxide in the
titration, you're removing both of the acidic hydrogens.

Isoelectric points, as the link you provide indicates, are only
relevant for amphoteric substances, such as metal oxides or amino
acids. Tartaric acid is not amphoteric.

If you titrate a strong acid HX with sodium hydroxide, then at the
equivalence point, all the acid will be converted to X-. Since HX is
a strong acid, X- is a very weak base, and will not affect the pH of
the solution. So the solution is neutral.

If you titrate a weak acid HA with sodium hydroxide, then at the
equivalence point, all the acid will be converted to A-, which is a
weak base. The A- anion will react with water via the reaction: A- +
H2O <==> HA + OH-. This means that there is a small amount of OH- in
solution, and the solution is basic.