Some reactions between substances take in heat and some give out heat. Exothermic reactions release lots of energy in the form of heat when they react whereas endothermic reactions absorb heat and therefore drop in temperature when reacting.
This practical contains four separate reactions where students predict and then record whether the reactions are exothermic or endothermic by using a thermometer or datalogger to record the temperature of the mixtures.
Equipment required (per set):
- Thermometers or dataloggers with temperature sensors
- 10cm³ sodium hydroxide solution (irritant)
- 10cm³ sodium hydrogen carbonate solution (irritant)
- 10cm³ dilute hydrochloric acid (irritant)
- 10cm³ copper (II) sulfate solution (irritant)
- 10cm³ dilute sulfuric acid (irritant)
- Four spatula measures of citric acid
- Four spatula measures of magnesium powder (highly flammable)
- 3cm magnesium ribbon (highly flammable)
All solutions should be made up to be around 0.4 mol dm-³.
The four experiments comprise two substances each and are as follows:
- Sodium hydroxide solution + dilute hydrochloric acid
- Sodium hydrogen carbonate solution + citric acid
- Copper (II) sulfate solution + magnesium powder
- Dilute sulfuric acid + magnesium ribbon
Pupils should take temperatures before mixing and during. All reactions are exothermic apart from the sodium hydrogen carbonate + citric acid which is an endothermic reaction.