Question 12

A student investigates the reaction of aqueous sodium hydroxide with two different aqueous solutions of hydrochloric acid, solution X and solution Y.

She carries out two experiments.

Experiment 1

Using a measuring cylinder, she pours $cm330\text{ cm}^3$ of aqueous sodium hydroxide into an insulated cup and records its temperature.
Using a burette, she adds $cm34\text{ cm}^3$ of solution X to the insulated cup.
She stirs the mixture with the thermometer and records the temperature.
She adds further $cm34\text{ cm}^3$ volumes of solution X and stirs with the thermometer.
She records the temperature after each addition of solution X.
She stops when a total of $cm332\text{ cm}^3$ of solution X has been added.

Experiment 2

She empties the burette and rinses it first with water and then with solution Y.
She then fills the burette with solution Y and repeats the experiment.

The table shows the results she obtains in Experiment 1:

Volume in $cm3\text{cm}^3$ of solution X added	Temperature in $∘C^\circ\text{C}$
0	19.0
4	22.2
8	25.4
12	28.6
16	29.4
20	27.8
24	26.2
28	24.6
32	23.0

Plot the results for Experiment 1 on the grid. Draw a straight line of best fit through the first four points and a second straight line of best fit through the last five points. Make sure that the two straight lines cross.

Graph paper grid with Temperature on y-axis from 15 to 32 and Volume of solution X added on x-axis from 0 to 35

Use the graph to determine the volume of solution X that will produce the maximum temperature rise when added to $cm330\text{ cm}^3$ of the aqueous sodium hydroxide.

Use the graph to determine the maximum temperature rise.

Why did the student rinse the burette first with water, and then with solution Y, before performing Experiment 2?

The maximum temperature rise in Experiment 2 was less than that in Experiment 1. Suggest a reason why.