Investigate a variable that affects the temperature change in reacting solutions. Here we compare acid concentration during neutralisation. Use 25 cm³ of hydrochloric acid each time and 25 cm³ of 1.0 mol/dm³ sodium hydroxide. Try acid concentrations of 0.2, 0.4, 0.6 and 0.8 mol/dm³. The alkali is in excess throughout.
1. Wear eye protection. Support a polystyrene cup inside a beaker.
2. Measure 25 cm³ acid into the cup. Measure 25 cm³ alkali separately. Let both reach the same starting temperature and record it.
3. Add the alkali, replace the lid and stir gently.
4. Read the temperature at regular short intervals until it starts falling. Record the highest reading.
5. Calculate the rise. Repeat with fresh solutions at each acid concentration, then repeat trials to calculate a mean.
| Change | Measure | Keep the same |
|---|---|---|
| Acid concentration | Temperature rise (°C) | Both volumes; alkali concentration; starting temperature; cup and lid; mixing and reading method |
The polystyrene cup and lid reduce unwanted energy transfer to the room. Stirring helps give an even temperature. Rinse and dry the cup between trials. Work in a supervised school practical; acids and alkalis can harm eyes.
Insulate, measure the start, mix and stir, find the maximum, subtract, repeat. Change one variable.
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