Scientific Skills

Question 1

Accuracy and precision

Answer 1

• 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

Question 2

Resolution

Answer 2

• 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

Question 3

Validity

Answer 3

• 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

Question 4

Techniques for improving data quality

Answer 4

• 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

Question 5

Systematic errors

Answer 5

• 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.

Question 6

Random errors

Answer 6

• 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.

Question 7

Personal errors / mistakes

Answer 7

• 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

Question 8

Repeatability and reproducibility

Answer 8

• 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