Experiment 5: Strong Acid/Strong Base Titration
We begin adding the basic secondary standard, NaOH, until our acid sample
solution turns very light pink, the
The point at which the indicator
changes color and the titration is stopped.
Theoretically, the sample volume of the sulfuric acid will still be colorless
at exactly to the point in which the numbers of moles H
completely neutralized by the OH
ions of our standard, the
The equivalence point occurs when all the H
ions from the acid and
ions from the base have been used up in the reaction. As a result,
solution is neutral; the pH = 7.
The equivalence point and the end point
do not necessarily coincide.
Therefore, the equivalence point and the end
point are separate terms with different meanings.
If we add more OH
ions than are needed to exactly neutralize the H
in the sample acid, then the solution becomes basic and the color changes to
pink. We want to add the sodium hydroxide until the solution is very slightly
pink (the end point). Ideally, the end point will equal the equivalence point.
However, when the color change of the indicator becomes visible, the [OH