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# paper 1 - EXPERIMENT 0 An Introduction to Scientific...

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Experiment 0- Page 1 EXPERIMENT 0 An Introduction to Scientific Measurements: Precision and Accuracy of Laboratory Glassware INTRODUCTION Volumetric Glassware Many of the compounds you will use in this laboratory course are in the form of aqueous solutions. You will therefore need to have several different kinds of volumetric glassware at your disposal. It is crucial for a chemist to be able to recognize when to make an accurate measurement or when to be satisfied with an approximate measurement, and to know which kind of glassware to use in each situation. In this experiment, you will determine the accuracy and precision of three different types of laboratory glassware which are used to measure the volume of liquid samples: a 10- mL volumetric pipet, a 10-mL graduated cylinder and a 10-mL beaker. Accuracy The term “accuracy” describes the nearness of a measurement to its accepted, or “true”, value. The accuracy of a given piece of glassware can be determined by measuring a specific amount of liquid with that glassware and then determining the volume of liquid it actually delivers. Since a pure substance has a specific density, the volume of liquid delivered can be measured by weighing the liquid and converting mass into volume using the mathematical relationship: ܦ݁݊ݏ݅ݐݕ ൌ ܯܽݏݏ ܸ݋݈ݑ݉݁ In this experiment, you will assess accuracy by calculating the percent error, as defined by the following equation: % ݁ݎݎ݋ݎ ൌ |ܧݔ݌݁ݎ݅݉݁݊ݐ݈ܽ ݒ݈ܽݑ݁ – ܶݎݑ݁ ݒ݈ܽݑ݁| ܶݎݑ݁ ݒ݈ܽݑ݁ ൈ 100 It is important to note that you cannot comment on the accuracy of an experiment unless you know the true value of the unknown you are investigating. In this experiment, the volume of liquid that the glassware under study actually delivers is the “true” value (its actual value) and the volume you are attempting to deliver is the “experimental” value. Precision The term “precision” describes the reproducibility of results. It refers to how closely multiple measurements of the same quantity, which have been made in an identical fashion, cluster to one another. Good precision does not mean that a result is accurate. In order to measure the precision of a piece of glassware, multiple measurements must be performed. However, because it would be too time-consuming for each student in the class to make multiple measurements for each type of glassware investigated in this experiment, you will perform only one measurement with each piece of glassware. Your class data will then be pulled to measure the precision of the glassware under study.

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