# Acid-base titration and equivalence point

## Material

Pipette and burette were previously rinsed with the solutions that will be introduced later.

## The start

A:
Acid or base concentration to be determined.
Volume $V_{Α}$ is measured using the pipette.
B:
Base or acid of known concentration.

## The term

P.e. : At the equivalent point $Α$ has completely neutralized $B$.
The P.e. is detected by the color change of an indicator or by the pHmeter.
The volume of $B$ added up to the P.e. is
$V_B$ $ = $ $V_2-V_1$

## The calculation

In P.e .:
The number of moles of added B is equal to the number of moles present before A added B.
$n_{Α} = n_B$
$c$_{Α}$V_{Α}=c_BV_B$

In P.e .:
$c_{Α}$ $=$ $\frac{c_BV_B}{V_{Α}}$

Example:
$20 \;mL$ of a $HCl$ solution of unknown concentration $c_{Α}$ accurately measured using the pipette, are introduced into the Erlenmeyer flask.
A drop of bromothymol is added.
The solution becomes yellow.
A solution of $0,10\frac{mol}{L}$ $NaOH$ is introduced in the burette.
We measure $V_1 = 10.5 mL $.
At the P.e. the solution turns blue.
We measure $V_2 = 25.5 mL $.
So we find:
$c_{Α}$ $ =$ $\frac{c_BV_B}{V_{Α}}$ $=$ $\frac{0.10\cdot(0.0255-0.0105)}{0.020}$ $= $ $0.075 \frac{mol}{L}$