Solution Preparation and Beers Law

Solution Preparation and Beers Law - SOLUTION PREPARATION...

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SOLUTION PREPARATION AND BEER’S LAW ADDITIONAL READING Concepts in this experiment are also discussed in sections 1.6, 2.8, 3.7, 4.4, 7.2, 12.3, 12.5 of Principles of Chemistry : A Molecular Approach , Nivaldo J. Tro [2010]. A history of Kool-Aid ® can be found at: http://www.hastingsmuseum.org/koolaid/kahistory.htm (checked 25-Oct-2009). ABSTRACT This is a two-part experiment. In part A, you and your lab partner will prepare solutions of your assigned Kool-Aid ® flavor(s). In part B, those solutions are used to construct standard Beer’s Law plots of absorbance vs. concentration. The best-fit lines for those plots are then used to determine dye concentrations in Kool-Aid ® of known and unknown dilutions. Background material includes topics not covered in your lecture text. The experiment employs the Vernier colorimeter; the Vernier system is used extensively in Gen Chem II Lab (Chem 1034). SOLUTION PREPARATION Solution preparation employs foundation lab skills: weighing rapidly as accurately as required, transferring material quantitatively, mixing thoroughly, measuring volumes, and calculating accurately. This experiment can help you assess and further develop your expertise. For quantitative work we need to know the amount of solute in solutions. Because it’s facile operationally, concentration is most commonly measured as molarity ( M ), which is defined as: n sol' L n M or solution of Liters solute of moles Molarity ( 1 ) Molarity is a measure of the number of solute molecules present per liter of solution. A mole is a named number (like a dozen or a googol); but at 6.022 x 10 23 , is more than the former (1.2 x 10 1 ) and less than the latter (10 100 ). A solution’s molarity is the number of moles (or fraction of a mole) of solute per liter of solution. The amount of solvent is not measured (contrast with molality, whose advantage is that mass can usually be measured more precisely than volume). PREPARATION OF A SOLUTION USING A PURE, SOLID SOLUTE For 3-4 significant figure accuracy, weighed, dry solute is dissolved in less than the required volume of solution in a volumetric flask (choose Class A for highest accuracy). Once dissolution (and adjusting to near the glassware’s calibration temperature, typically 20°C) is complete, add solvent, and mix again. Add more solvent with a transfer pipet to bring the solution level up to the fill line on the flask’s neck. The bottom center of the liquid’s meniscus should be level with the top of the line. Stopper or cap the flask; hold the top in place and support the base. Repeatedly invert the flask gently, swirl it, and revert it until mixing is essentially complete (up to 40 times, at least a few times beyond when inhomogeneity – streaking – is still visible). For example, how should 250 mL of 0.200 M CuSO 4 solution be prepared given copper(II) sulfate pentahydrate CuSO 4 · 5H 2 O (lovely blue crystals) and deionized (DI) water?
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This note was uploaded on 04/19/2011 for the course CHEM 1033 taught by Professor Price during the Fall '10 term at Temple.

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Solution Preparation and Beers Law - SOLUTION PREPARATION...

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