Measuring with Uncertainties

The video introduces the concept of recording measurements with uncertainties, a common practice in science classes, using examples from chemistry and an electronic balance.

When reading a burette, you read from the bottom of the meniscus. The instrument is capable of measuring to a hundredth of a milliliter. The uncertainty for glass instruments like a burette is half of the smallest increment. For example, a reading of 20.00 mL would have an uncertainty of ±0.05 mL.

For a graduated cylinder, the last digit recorded is your best guess. Similar to the burette, the uncertainty is half of the smallest subdivision. For instance, a reading of 6.83 mL would have an uncertainty of ±0.05 mL.

When using a ruler, the smallest subdivision is typically a tenth of a centimeter (a millimeter). The uncertainty is half of this smallest subdivision. So, a measurement like 1.73 cm would have an uncertainty of ±0.05 cm.

For digital instruments like an electronic balance, the uncertainty is determined by the last place value displayed. For example, if a balance reads 175 grams, the uncertainty is ±1 gram. If it reads 0.98 grams, the uncertainty is ±0.01 grams, essentially placing a '1' in the last significant digit's position. This rule is a general guideline, as some devices may have specified uncertainties.

When recording multiple measurements in a lab report, you can state the uncertainty at the top of the column for convenience instead of after each individual measurement.