Recording Data (DP IB Chemistry: SL)

• When recording results of experiment, both quantitative and qualitative data should be obtained
• Quantitative data is obtained from measurements whereas qualitative data is non-numerical information that comes from observations
• Quantitative data is always associated with random errors/uncertainties, determined by the apparatus, and by human limitations such as reaction time
• Where there are several items of data you should record your data in a table with appropriate headings and units:

Data Table showing headings and units

• Uncertainties are the same as random errors
• Uncertainties express the confidence to which the measurement can be taken
• Treatment of uncertainties depends on the type of instrument used

Using analogue instruments

• Any instruments that have an analogue scale, the uncertainty is taken as half the smallest division on the scale
• For example,
  • A thermometer that reads to 1^oC, the uncertainty would be +0.5 ^o C
  • A burette that reads to 0.10 mL, the uncertainty would be +0.05 mL

Using digital instruments

• Any instruments that have a digital scale, the uncertainty is taken as the smallest division on the scale
• For example,
  • An electronic balance that reads to 0.01 g, the uncertainty would be +0.01 g

Other uncertainties

• Other sources of uncertainty can arise where the judgement of the experimenter is needed to determine a changing property
• For example,
  • Judging the end point of a titration by looking at the colour of the indicator
  • Controlling a stopwatch in a rate of reaction experiment
  • Deciding when to extinguish the flame in an enthalpy of combustion experiment

• These uncertainties are very difficult to quantify, but they should be commented on as a source of error in an evaluation