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Winter 2006 1 2 ( REVISED ) - S OLUTIONS , C ONCENTRATIONS , B EER S L AW Topics for Study : Techniques Videos (“Use of a Pipet” and “Solutions Preparation”), concentrations, Beer’s Law and Chapter III in the lab manual. Glossary : molarity, ppm, ppb, colorimeter, cuvette, absorbance, transmittance T ECHNIQUES In this assignment you will use the following procedures: Manipulative skills use an analytical balance make a volumetric solution use a volumetric pipet perform serial dilutions take measurements on a colorimeter Theoretical skills calculate the molar concentration of a solution calculate serial dilution concentrations convert between the units of molarity, weight/volume percent, ppm, ppb. use a calibration curve to determine a concentration study the spectrum of a compound S AFETY Always wear safety glasses or goggles and a protective lab coat or apron. Brilliant Blue FCF * , the food coloring dye, that you will use in this experiment, is intensely colored. Wear gloves and handle the dye carefully avoiding spilling on the balance or bench top. Wipe any spills immediately and wash any residue with large quantities of water. B ACKGROUND Preparing solutions with specific concentrations or within a range of concentrations constitutes a fundamental skill for any lab scientist. Whether these solutions are prepared by dissolving a solid in the solvent, or by diluting other solutions whose concentrations are known, depends on the circumstances of the experiment, the concentration needed, and the precision required. This last factor, the precision needed, often dictates what equipment and what technique must be used. There are many concentration units. Tradition in a discipline and ease of use for a specific purpose frequently determine which unit is used at a given context. Chemists tend to use molarity because it facilitates understanding the stoichiometric relationships that are being studied; biochemists use millimoles and microliters to simplify the numbers when they are using very small amounts and very dilute solutions; oceanographers and geologists use parts per million to describe trace concentrations of materials in large water bodies and in ores; analysts * Disodium salt of ethyl [4-[p-[ethyl (m-sulfobenzyl) amino]- α -(o-sulfophenyl) benzylidene]-2,5-cyclohexadien-1- ylidene] (m-sulfobenzyl) ammonium hydroxide. It is obvious why the common names, Brilliant Blue FCF or Food Blue 2 are used.
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Winter 2006 2 often use weight percent because it simplifies the instructions for preparing standard stock reagents. Converting among units should be a routine task. B EER S L AW Electromagnetic radiation, energy propagated through space by electrical and magnetic disturbances, is oftern described in terms of the wave parameters of wavelength and frequency.
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