Monitoring chemical reactions

Medium

A student carries out a titration to determine the concentration of a sample of sodium hydroxide ( $N a O H$ ).

They use:

$cm325.0\text{ cm}^3$ of dilute sodium hydroxide in a conical flask.
Hydrochloric acid ( $H C l$ ) of concentration $mol/dm30.200\text{ mol/dm}^3$ in the burette.

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

Titration number	1	2	3	4
Final burette reading ( $cm3\text{cm}^3$ )	19.6	38.0	19.5	37.2
Initial burette reading ( $cm3\text{cm}^3$ )	0.0	19.6	1.0	19.5
Titre (volume of acid used) ( $cm3\text{cm}^3$ )	19.6	18.4	18.5	17.7

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

[2]

The equation for the reaction is: $\rightarrow NaCl + H_2O$

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

[6]

Monitoring chemical reactions Questions