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August+24+Expt+1+Accuracy+and+Precision

August+24+Expt+1+Accuracy+and+Precision - Chem 1310H Exp 1...

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- 1 - Chem 1310H Exp 1 Accuracy, Precision, Statistics, and Beer’s Law Objectives: Reiterate basic analytical measuring techniques such as correctly using volumetric glassware and dilutions from the prior laboratory. Intorduce absorption spectroscopy. Expand on the available statistical methods by introducing the Q-test for measurements. Introduction: Accuracy & Precision: Chemistry is a measurement science. Good observations, knowing the limitations of laboratory equipment and understanding when data is meaningful are the mark of an good scientist. Mass and volume measurements are perhaps the most often made measurements in chemistry. Many people use the words precision and accuracy interchangeably but to scientists they have separate meanings. Precision is the reproducibility of a measurement or how closely measurements agree with one another. The number of significant figures used in a measurement or statistical figures of merit such as average, standard deviation and confidence intervals are used to describe the precision of a measurement. Accuracy is how close a measurement comes to the real or actual value. Accuracy requires that a known standard or careful calibration of an instrument. A common depiction of these two concepts is a bull’s eye where the center circle is the “correct” or most accurate value. Figures of merit associated with accuracy are % error and % deviation (from true value) Glassware and plastic ware used in a lab usually have volume measurements on them. It is very important to know the precision of the glassware used and when an approximate volume will do and when more precision is called for in measurements. Typically, graduation on beakers and Erlenmeyer flasks are not very precise and must only be used when very approximate volumes are needed. More precise glassware is called “analytical or volumetric glassware” and consists of graduated cylinders, pipets and burets. Experiment 1
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