Question 14

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

She carries out two experiments.

Experiment 1

Using a measuring cylinder, she pours $cm330\text{ cm}^3$ of aqueous sodium hydroxide into a polystyrene cup and records its initial temperature.
Using a burette, she adds $cm36\text{ cm}^3$ of Acid X to the cup.
She stirs the mixture with the thermometer and records the temperature.
She adds further $cm36\text{ cm}^3$ volumes of Acid X and stirs with the thermometer.
She records the temperature after each addition of Acid X.
She stops when a total of $cm348\text{ cm}^3$ of Acid X has been added.

Experiment 2

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

The table shows the results she obtains in Experiment 1:

Volume of Acid X added / $cm3\text{cm}^3$	Temperature / $∘C^\circ\text{C}$
0	18.5
6	22.7
12	26.9
18	28.4
24	27.2
30	26.0
36	24.8
42	23.6
48	22.4

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

Graph Grid

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

(ii) Use the graph to determine the maximum temperature rise.

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

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