Skills in Chemistry- uncertainties, errors etc.
● Understand the significance of uncertainties in raw and processed data.
● Record uncertainties in measurements as a range (±) to an appropriate level of precision.
● Propagate uncertainties in processed data, in calculations involving addition, subtraction, multiplication, division and (HL)
exponents.
● Express measurement and processed uncertainties: absolute, fractional (relative), percentage—to an appropriate number of
significant figures or level of precision
- Qualitative datais non-numerical information thatcan be gathered from observations.
- Quantitative datais the numerical data found fromtaking measurements.
- Erroris the difference between the measurement orthe value that has been found and the true (or accepted) value.
- Accuracyis an indication of how close values areto the accepted or true value.
- Precisionis an indication of how close together repeatedmeasurements are.
- If a student repeats the experiment and gets the same results each time, they are said to berepeatable.If another student repeats
the method and gets the same results, the results are now said to bereproducible.
- If you are referring to an individual measurement,precisioncan also be taken to mean the number ofsignificant figures to which a
value is given.
- Uncertaintyis an estimate of the doubt that we haveabout our measurement, due to the random error of an instrument.
- Uncertainties are quantified and are given an upper and lower range using the symbol ‘±’.
- On agraduated scale, the tolerance is ±halfof thesmallest scale division.
- On adigital scale, the uncertainty should be quotedas ± 1 as the last decimal place it shows.
- When recording raw data in your results, measurements on the same instrument should be recorded to the same level of precision – i.e
the same number of decimal places – and thesame uncertainty.
- In calculations, the final value determined can only be quoted to the number ofsignificant figuresofthe ‘worst’ measurement.
- Zeros at the end of a numberare always significantif the number contains a decimal point.
- If youadd or subtract valuesin calculations, itis actually the number ofdecimal placesthat matters.Values to be quoted to the
least number of decimal places given in the measurements.
- If you aremultiplying or dividing values, it is thesignificant figures that are relevant. The number with the fewestsignificant figures
used in the calculation determines how many significant figures should be used in the final answer.
𝑎𝑏𝑠𝑜𝑙𝑢𝑡𝑒𝑢𝑛𝑐𝑒𝑟𝑡𝑎𝑖𝑛𝑡𝑦
- %𝑢𝑛𝑐𝑒𝑟𝑡𝑎𝑖𝑛𝑡𝑦 = 𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑚𝑒𝑛𝑡
× 100
- Averaging values:You may record the uncertainty ofthe mean (average) as the uncertainty of a single reading.
- Adding or subtracting values:You should add the absoluteuncertainties together.
● Understand the significance of uncertainties in raw and processed data.
● Record uncertainties in measurements as a range (±) to an appropriate level of precision.
● Propagate uncertainties in processed data, in calculations involving addition, subtraction, multiplication, division and (HL)
exponents.
● Express measurement and processed uncertainties: absolute, fractional (relative), percentage—to an appropriate number of
significant figures or level of precision
- Qualitative datais non-numerical information thatcan be gathered from observations.
- Quantitative datais the numerical data found fromtaking measurements.
- Erroris the difference between the measurement orthe value that has been found and the true (or accepted) value.
- Accuracyis an indication of how close values areto the accepted or true value.
- Precisionis an indication of how close together repeatedmeasurements are.
- If a student repeats the experiment and gets the same results each time, they are said to berepeatable.If another student repeats
the method and gets the same results, the results are now said to bereproducible.
- If you are referring to an individual measurement,precisioncan also be taken to mean the number ofsignificant figures to which a
value is given.
- Uncertaintyis an estimate of the doubt that we haveabout our measurement, due to the random error of an instrument.
- Uncertainties are quantified and are given an upper and lower range using the symbol ‘±’.
- On agraduated scale, the tolerance is ±halfof thesmallest scale division.
- On adigital scale, the uncertainty should be quotedas ± 1 as the last decimal place it shows.
- When recording raw data in your results, measurements on the same instrument should be recorded to the same level of precision – i.e
the same number of decimal places – and thesame uncertainty.
- In calculations, the final value determined can only be quoted to the number ofsignificant figuresofthe ‘worst’ measurement.
- Zeros at the end of a numberare always significantif the number contains a decimal point.
- If youadd or subtract valuesin calculations, itis actually the number ofdecimal placesthat matters.Values to be quoted to the
least number of decimal places given in the measurements.
- If you aremultiplying or dividing values, it is thesignificant figures that are relevant. The number with the fewestsignificant figures
used in the calculation determines how many significant figures should be used in the final answer.
𝑎𝑏𝑠𝑜𝑙𝑢𝑡𝑒𝑢𝑛𝑐𝑒𝑟𝑡𝑎𝑖𝑛𝑡𝑦
- %𝑢𝑛𝑐𝑒𝑟𝑡𝑎𝑖𝑛𝑡𝑦 = 𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑚𝑒𝑛𝑡
× 100
- Averaging values:You may record the uncertainty ofthe mean (average) as the uncertainty of a single reading.
- Adding or subtracting values:You should add the absoluteuncertainties together.
