Temperature changes during neutralisation
Experiment
Method
Results
Analysis
Video
This experiment investigates the temperature change when an acid reacts with an alkali.
NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l)
The reaction is carried out in a polystyrene cup fitted with a lid. The lid has a hole so that a thermometer can be placed inside the cup
and the temperature change measured. The cup is placed in a beaker to prevent it toppling over.
What is the advantage of using a polystyrene cup?
Polystyrene foam is a good insulator and helps to reduce heat losses.
Step 1
The cup initially contain 30 cm³ of 2M HCl. Record the starting temperature.
Step 2
Click the "Add NaOH" button to add 5 cm³ of sodium hydroxide to the cup. Record the new temperature.
(In a real experiment, you would stir the solution and record the highest temperature reached.)
Step 3
Repeat the above until you have added 40 - 50 cm³ of NaOH.
Step 4
Click the "Reset" button and repeat the whole experiment.
Record your results in a table like the one shown on the left.
You can plot a small graph in the simulation by clicking the "Plot point" button. Click on a point to remove it from the graph.
The "Clear all" button removes all the points.
However this is only a rough graph and you should also plot accurate graphs on graph paper.
Plot a graph of the average temperature against the volume of NaOH added.
Draw two best fits lines or curves through your points - one where the temperature is increasing and one where the temperature is decreasing.
Why does the temperature rise and then fall?
The temperature rises because heat is produced when the acid and alkali react. Once all the acid has reacted, no more heat can be produced,
so you are just adding cold (20 °C) alkali and therefore the solution cools down.