Scientific Skills Flashcards

1
Q

Accuracy and precision

A
  • Accuracy – how close an experimental measurement is to the known or true value
    • Bull’s eye on a target
  • Precision – how close multiple measurements of the same investigation are to each other
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2
Q

Resolution

A
  • Small change in the measured quantity that causes a big change in the value shown by the measuring instrument
  • This has implications for the number of decimal places that should be quoted
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3
Q

Validity

A
  • How successfully an experiment measures what it is intended to measure; whether it tests the set hypothesis and aims
  • To ensure validity, only 1 variable should be changed at a time
    • Allows meaningful conclusions to be drawn about the effect of each variable
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4
Q

Techniques for improving data quality

A
  • Calibration – adjusting an instrument using a standard allows for more certainty that measured values are accurate
  • Equipment – pipettes or burettes are more precise than measuring cylinders when measuring volumes of liquids
  • Sample size – generally, the larger the sample (e.g. mass of substance used), the more precise the measured values will be
    • Percentage error will be smaller for the larger mass
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5
Q

Systematic errors

A
  • Produce a constistent bias in a measurement that cannot be eliminated by repeating the experiment
    • Error will be in the same direction for each measurement and the average will either be too high / too low as a result
  • Usually due to equipment or system errors
    • E.g. uncalibrated pH meter consistently records inaccurate pH value or an unsuitable indicator being used in a titration
  • Can be reduced by using equipment carefully, calibrating equipment before use and reviewing the experimental method

NOTE: Systematic errors affect the accuracy of measurements.

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6
Q

Random errors

A
  • Unpredictable (chance) variations in measurements
    • Follow no regular pattern
  • Usually due to sudden environmental changes or unreliable measuring instruments
    • E.g. temperature variation within a solution that has not been mixed consistently or an error in estimating the colour of an indicator
  • Their effect can be reduced by taking multiple measurements then calculating a mean / average

NOTE: Random errors affect the precision of measurements.

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7
Q

Personal errors / mistakes

A
  • Avoidable mistakes / miscalculations made by the observer
  • E.g. misreading numbers on a scale or spilling a portion of a sample
  • Can be prevented by carefully carrying out the experiment
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8
Q

Repeatability and reproducibility

A
  • Repeatability – how close measurements are to each other in identical conditions
    • Observer repeats the experiment and produces the same results
    • Maintained by sufficiently replicating the experiment
  • Reproducibility – how close results are when the same variable is being measured under different conditions
    • Other people repeat the experiment and produce the same results
    • Beneficial to analyse as it helps identify potential systematic errors that would affect the accuracy of the experiment
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