A student investigates the temperature change when citric acid solution is mixed with sodium hydrogencarbonate solution.
The two solutions have the same starting temperature. The student mixes them in a polystyrene cup, stirs the mixture and puts on a lid with a thermometer through it.
The student records the temperature once, 2 minutes after mixing.
| Measurement | Temperature (°C) |
|---|---|
| Starting temperature of the solutions | 20.5 |
| Temperature 2 min after mixing | 14.0 |
Calculate the temperature change.
temperature change = temperature after 2 min − starting temperature
Temperature change = ............... °C
State whether the reaction is exothermic or endothermic.
The student repeats the experiment in two different cups, P and Q. The same volumes and concentrations of the solutions are used in each cup.
| Cup | Starting temperature (°C) | Temperature 2 min after mixing (°C) |
|---|---|---|
| P | 20.5 | 13.0 |
| Q | 20.5 | 15.5 |
Which cup is better insulated?
Explain your answer using the results.
Give one reason why the student stirs the mixture before taking a temperature reading.
The student takes only one temperature reading after mixing.
Suggest one improvement that would help the student find the lowest temperature reached.
106 exam-style questions on OCR GCSE Chemistry 3.2 Energetics, covering 3.2.1 Exothermic and endothermic reactions and reaction profiles and 3.2.2 Calculating energy change from bond energies. Each one has a worked solution and a mark scheme showing where the marks go.