Question

Titration of acetic acid

. Error analysis. Suppose during the titration vou added NaOH sufficient to change the indicator to a much darker pink color. How would this affect your experimental result? Would this increase or decrease your experimental acetic acid content? Explain.

Answer 1

This is an example of titration between strong base and weak acid.

The NaOH dissociates entirely when it is added dropwise before reacihng the end point.

It  generates  OH^-. The OH^- is a strong base so it will add with any H⁺ that is around.

Since at beginning small amount of the OH^- will drive the dissociation of the weak acid until all the OH^- is absorbed into water.

the solution behaves like a buffer.

As more and more NaOH is added in excess, but the pH tends to rise only  little because there is still many CH₃COOH molecules around to supply the free H⁺ to absorb the OH^-.

After enough OH^- will be added that almost all all of the CH₃COOH dissociates.
At this equivalence point, [OH^-] = [CH₃COOH] and [Na⁺] = [CH₃COO^-].

So the result of acetic acid concentration would vary if more NaOH is added even after the end point.

As more NaOH is added, the pH increases steeply to the equivalence point and  the amount of OH^- added equals the amount of initial weak acid.