Question Constellation Sign up for free AQA · GCSE · Chemistry · Higher
Explaining random experimental errors
A student investigated the energy change of the reaction between zinc and copper sulfate solution.
- Measure 25 cm³ of copper sulfate solution into a polystyrene cup.
- Measure the temperature of the copper sulfate solution.
- Add 0.20 g of zinc powder to the copper sulfate solution.
- Stir the reaction mixture.
- Record the highest temperature reached.
- Repeat steps 1 to 5 with different masses of zinc powder.
A different student repeated steps 1 to 5 of the method four times using 0.50 g of zinc powder.
| Trial 1 | Trial 2 | Trial 3 | Trial 4 | |
|---|---|---|---|---|
| Highest temperature reached in °C | 37.6 | 37.2 | 37.8 | 37.4 |
The results show random errors. The student did not make any measuring errors. Suggest one reason for the random errors in this experiment.
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Marking points
- 1 Suggests one credited source of trial-to-trial variation: different starting temperature, inconsistent stirring, or inconsistent use of a lid.
Full-mark answer
The amount of stirring may have varied between trials.
Why this answer loses marks
The thermometer was read incorrectly.
The prompt rules out measuring errors; identify a trial condition that could vary instead.