Monitoring chemical reactions

Medium

A student carries out a titration to determine the concentration of a sample of nitric acid ( $HNO_3$ ).

They use:

$cm325.0\text{ cm}^3$ of dilute nitric acid in a conical flask.
Potassium hydroxide ( $K O H$ ) solution of concentration $mol/dm30.150\text{ mol/dm}^3$ in the burette.

The student's titration results are shown in the table below:

Titration number	1	2	3	4
Final burette reading ( $cm3\text{cm}^3$ )	24.8	25.1	24.0	26.2
Initial burette reading ( $cm3\text{cm}^3$ )	0.0	1.5	0.5	2.0
Titre (volume of alkali used) ( $cm3\text{cm}^3$ )	24.8	23.6	23.5	24.2

Explain why the student should only use the results from titration numbers 2 and 3 to calculate the average titre.

[1]

The equation for the reaction is: $HNO3+KOH→KNO3+H2OHNO_3 + KOH \rightarrow KNO_3 + H_2O$

Calculate the concentration of the nitric acid in $mol/dm3\text{mol/dm}^3$ .

[6]

Monitoring chemical reactions Questions