Lab_1_SpecMod10

Lab_1_SpecMod10 - Spectrophotometry, Beer's Law, and...

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Chem 223 – Spectrophotometry, Beer's Law, and Precision -1- Spectrophotometry, Beer's Law, and Precision Fall, 2010 SAFETY FIRST! Remember to bring AND WEAR your goggles. "But we aren't doing any reactions this week, and the chemicals are largely innocuous." "They're hot and steam up." "They're uncomfortable." "I forgot." "I look like I came from Mars." We've heard 'em all. Doesn't matter. You'll be in a lab. Get to the point that it's a reflex: BRING AND WEAR YOUR SAFETY GOGGLES. Simple way to tell if you've been careful this week: if you don't have blue or violet fingers, you did fine. (Methylene blue is used to stain tissue during surgery, so it's safe, just ugly.) Purpose Analytical Chemistry is the science that identifies the components of a portion of the physical world, quantifies them, and characterizes their interactions. Doing this requires: A problem whose solution requires knowledge of chemical composition or dynamics. One or more means of measurement An understanding of the chemistry and physics that effects the measurement A means to characterize the quality of the measurement (both precision and accuracy) A theoretical or practical way to use the results of the measurement to solve a problem. Our purpose here is to demonstrate a common means of measurement (spectrophotometry), to show examples where the measurement tool works, to show examples where the measurement tool fails, and to show examples where the chemistry interferes with the measurement. All this will be done under circumstances where the operator's manual dexterity is of minimal or no influence on the results. In later labs, your skill will contribute to the precision of the experiment. Many past students have felt that imprecision was some mark of shame or that "skill is proportional to 1/standard deviation." There are times when this is true, but in this experiment you will see differences in uncertainty caused by chemistry, sample, and instrument. What you should learn is: Non-zero uncertainty is a fundamental property of nature. Many factors contribute to uncertainty. Understanding the sources of uncertainty can lead to their minimization. Learning analytical chemistry means learning the "tools of the trade" PLUS developing "lab technique" PLUS learning how to integrate many pieces of information into the solution of a single problem. Background One of the hardest parts of doing analytical chemistry is that we must deal with the world as a SYSTEM (many things interacting and happening at once), yet we have been taught to deal with learning and living as COMPONENTS (single activities, single calculations, individual controls or pieces of apparatus). Think of driving a car. You don't think about each spark plug firing or turning the wheel 2.78º to the right or pushing on the gas pedal by an additional 10 -3 Newtons to accelerate. You Just Drive. You are taking a systems approach, with a lot of activity implicit in what you do. But when you learned to drive, you DID pay attention to pressure on the gas or the angle at which you steered.
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Lab_1_SpecMod10 - Spectrophotometry, Beer's Law, and...

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