3.4 Measurements and uncertainty
5 exam questions worth 8 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.
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Repeat results that are very close together are described as:
Choose one answer.
Correct Not quite: the answer is Precise
Mark scheme
B
Model answer
B: precise results have a small spread.
A student measured the volume of gas produced three times: 46 cm3, 50 cm3 and 48 cm3.
Calculate the mean volume.
Mark scheme
- (46 + 50 + 48) ÷ 3 = 48 cm3 (1)
Model answer
(46 + 50 + 48) ÷ 3 = 144 ÷ 3 = 48 cm3.
Use the results in the previous question to estimate the uncertainty in the mean. Give your answer as mean ± uncertainty.
Mark scheme
- range = 50 − 46 = 4 cm3, half = 2 (1)
- 48 ± 2 cm3 (1)
Model answer
Range = 4 cm3, so the uncertainty is ±2 cm3: 48 ± 2 cm3.
A student records times of 31.2 s, 30.8 s, 36.5 s and 31.0 s.
Identify the anomalous result and calculate the mean of the other results.
Mark scheme
- 36.5 s (1)
- (31.2 + 30.8 + 31.0) ÷ 3 = 31.0 s (1)
Model answer
36.5 s is anomalous. The mean of the others is 93.0 ÷ 3 = 31.0 s.
Give two ways a student could reduce the uncertainty when measuring the volume of acid used in a reaction.
Mark scheme
any two from:
- use a burette / pipette instead of a measuring cylinder (higher resolution) (1)
- repeat and calculate a mean (1)
- measure a larger volume (1)
Model answer
Use a burette, which has a higher resolution than a measuring cylinder, and repeat the measurement to calculate a mean.
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