GCSE Chemistry (AQA)

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Uncertainty

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Quantitative chemistry Chemical measurements, conservation of mass and the quantitative interpretation of chemical equations

Uncertainty

6:06 Conservation and Changes of Mass in Chemical Reactions
Spec 4.3.1.4
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  • Apparatus used in chemistry for measuring liquid volumes include pipettes, burettes, and measuring beakers.
  • The choice of apparatus depends on the volume needed and the purpose, e.g., burettes are preferred for titrations.
  • Measurement uncertainty arises due to equipment precision, which affects reliability.
  • Uncertainty can be estimated from repeated measurements.
  • Example experiment: measuring hydrogen gas volume collected in two minutes using a gas syringe.
  • Anomalous results should be ignored when calculating the mean.
  • Example: 96 is an anomalous result; mean calculated from 75, 78, 80, 74 is 76.75 cm��.
  • Uncertainty is calculated as half the difference between the highest and lowest values.
  • Example: difference between 80 and 74 is 6, giving an uncertainty of 3 cm��.
  • Results are recorded as mean �� uncertainty, e.g., 76.75 �� 3 cm��.
  • Another example: measuring HCL volume to neutralize NAOH, ignoring anomalous 31.25.
  • Mean calculated from 22.50, 22.80, 22.65 is 22.65 cm��.
  • Difference between highest (22.80) and lowest (22.50) is 0.3, giving uncertainty of 0.15.
  • Final result: 22.65 �� 0.15 cm��.

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