Chemistry 112 Copper in a Penny - Drew Rasmussen Partner:...

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Drew RasmussenPartner: JayInstructor: Katri TruhlerChemistry 112 LabMarch 24, 2011Colorimetric Determination of Copper in a PennyA.Research Question:a.What is the percentage of copper in the assigned penny?B.Theoretical Approach:a.From Beer’s Law we know that concentration and absorbance are directly related,thus as concentration increases absorbance will increase, and as concentrationdecreases, so will absorbance.With CuSO4* 5H2O a standard curve can becreated by generating different stock solutions, varying only by concentration.Bygraphing the Absorbance vs. Concentration of our 6 standard solutions we shouldget a relatively linear line (and an equation for the line) that can be used todetermine the percentage of copper in our penny by simple calculations, andplugging in the absorbance reading of our penny at a maximum wavelength.C.Observations and Results:a.The penny used was a 1986 penny, that was relatively clean for its age. It wasn’ttoo tarnished, and it was in good shape. It weighed 2.540g (+ or – 0.001g).b.Our group was assigned a stock solution of 0.100g of Copper per 250 mL.Through calculations and knowing the molecular weight of CuSO4* 5H2O, wecalculated that 0.392g of the solid would have to be added to produce our
assigned concentration.CuSO4* 5H2O is a blue crystal that looks a lot like sugaror salt.It has a very faint sweet aroma, and dissolves easily in water.Whenadded to water it has a light opaque blue color.Ammonium hydroxide is a verypotent chemical, it burned my nostrils upon wafting it (must be veryconcentrated).After the addition of 4.9mL of Ammonium hydroxide to ourCopper and Water solution, the entire solution became a very deep royal bluecolor.Once diluted to the 250mL mark on the volumetric flask it was a bit lighterin appearance, but had the same general color.Our standard solution produced anabsorbance of 0.369.When the nitric acid was poured on the penny, bubblesbegan forming rapidly shifting the penny throughout the liquid.This was a veryviolent reaction causing a Turquoise liquid to form as the concentrated aciddissolved the penny.As the penny was dissolving copper colored smoke wascoming out of the beaker.As the reaction is coming to an end, the smoke

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Term
Spring
Professor
LEMASTER
Tags
Chemistry, Penny Year

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