Uncertainties and Measurement Errors

Below are the key elements to consider when revising the topic “Uncertainties and Measurement Errors” in context to Formulae, Equations and Amounts of Substances:

• Understand that all measurements in chemistry have some degree of uncertainty, due to the limitations of the measuring equipment or the person using it.

• It is important to quantify and minimise these uncertainties as they have potential to change or influence the overall result or conclusion.

• Uncertainty can be estimated as half of the smallest division in a measuring instrument. For example, on a measuring cylinder where 1 mL is the smallest division, the estimated uncertainty would be 0.5 mL (half of the smallest division).

• Random errors occur when measurements show variability around the true value. For example, if you weigh the same substance numerous times and get slightly different results each time, these are considered random errors.

• Systematic errors are consistent, repeatable errors associated with faulty observations or instruments. An instance of this could be using a zeroed balance incorrectly, causing all the subsequent mass measurements to be inaccurate by the same amount.

• To reduce uncertainties or errors, multiple readings are taken and the mean of these readings is calculated. This process can help to decrease random errors.

• Understand the difference between precision and accuracy. Precision refers to how close the measurements are to each other while accuracy refers to how close these measurements are to the true value.

• Absolute uncertainty refers to the uncertainty of a measurement itself, whereas relative (or percentage) uncertainty refers to how significant that uncertainty is compared to the overall measurement.

• When calculating percentage uncertainties for multiplication and division, sum your percentage uncertainties. For addition and subtraction, sum your absolute uncertainties.

• Understand error propagation during different mathematical operations. For instance, when adding or subtracting, errors add up; when multiplying or dividing, percentage errors add up.

• Ensuring correct use and calibration of measuring instruments is a fundamental part of reducing measurement errors and uncertainties.

Remember, the aim is to achieve results with smaller uncertainties, increasing their reliability and validity.