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Improving temperature-change method
A student investigated the temperature change when different masses of magnesium carbonate were reacted with excess nitric acid.
Figure 6 shows the apparatus.
This is the method used.
- Pour 50 cm³ of nitric acid into a polystyrene cup.
- Measure the temperature of the solution.
- Add 0.50 g of magnesium carbonate.
- Stir the mixture.
- Measure the temperature.
- Repeat steps 1 to 5 with different masses of magnesium carbonate.
Give two improvements to the method to produce more accurate results. Do not refer to improvements to the apparatus in your answer.
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Marking points
- 1 Repeats each mass condition and calculates a mean, discarding anomalous results where appropriate.
- 2 Measures the highest temperature reached rather than taking an unspecified single final reading.
Full-mark answer
Repeat the experiment several times for each mass, discard anomalous results and calculate a mean. Record the highest temperature reached for each trial.
Why this answer loses marks
Add a lid to the cup.
The question excludes apparatus changes; the credited method changes are repeat-and-average handling and measuring the highest temperature reached.