Temperature change

Investigate the variables that affect temperature change in chemical reactions.

In this required practical, students are assessed on their ability to measure, record and plot the temperature changes occurring in a chemical reaction. They are to do this by reacting Sodium Hydroxide and Hydrochloric Acid. They will produce a graph of their results and draw two lines of best fit to identify the intersection point. The students use of equipment and chemicals in a safe manner is also observed during the practical session.

Equipment (per participant)

• Safety goggles
• Insulated cups
• 250ml beaker
• Thermometers
• 50ml measuring cylinder
• Hydrochloric Acid (2M)
• Sodium Hydroxide (2M)
• CLEAPSS Hazcards: 47A, 91A

Method

Students should collect the necessary equipment. The insulated cup needs to stand in a 250ml beaker to improve its stability during the experiment.
30mls of Hydrochloric Acid is measured out using a measuring cylinder and is carefully poured into the insulated cup. The measuring cylinder should now be thoroughly rinsed with water. Using a thermometer, students should measure the starting temperature of the acid and record this in an appropriate table.
The students then measure 5mls of Sodium Hydroxide using the measuring cylinder and pour this into the insulated cup. The cup is fitted with a lid (a small square of cardboard is appropriate if plastic lids are unavailable) and the thermometer is inserted through a hole in the lid so that it can be used to stir the solution in the cup.
Students must watch the temperature rise on the thermometer. When the reading on the thermometer stabilises, they need to record the maximum temperature reached.
Students then repeat the process by adding a further 5mls of Sodium Hydroxide, recording the maximum temperature reached each time until they have added 40mls of Sodium Hydroxide in total.
Students should then wash out their equipment and repeat the whole process for a second trial.
The mean maximum temperature values can now be calculated for each addition of Sodium Hydroxide.

Technician tips

Lids for the insulated cups could be made using a small square of cardboard. A hole can be made through the cardboard, using a sharp pencil, through which a thermometer can be inserted. These could be pre-made for students to save time during the practical session.
Polystyrene cups are no longer widely available to purchase. Schools can re-use these where possible until the end of their supply is reached. An insulated paper drinks cup is a good replacement for use during this practical.