How much copper is in a penny - Calculating the Amount of Copper in a Penny Dan Ocampo Chemistry Lab 144 A Yasmin Jessa T.A Daniel Drew Lab partner Zach

How much copper is in a penny - Calculating the Amount of...

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Calculating the Amount of Copper in a Penny Dan Ocampo Chemistry Lab 144 A Yasmin Jessa T.A.: Daniel Drew Lab partner: Zach Nield & Eric Pascoe 11 November 2013 Introduction : 1
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The objective of this lab experiment is to dissolve and calculate the percent of copper in a penny. However, to do this some background information must be known first. A strong oxidizing agent is required to oxidize copper, like nitric acid. This oxidizing agent also creates nitrogen dioxide and complex ions. This complex ions, (Cu(H 2 O) 4 2+ ) & (Zn(H2O) 4 2+ ), contain ligands which must be displaced by a stronger base like ammonia (NH 3 ) to produce a different complex ions. These complex ions have respective colors which provide an opportunity to determine the concentration of copper without interference from the large concentration of Zinc in the pennies. The Beer-Lambert Law states that “Molecular species absorb and emit light energy that corresponds to an electronic transition in the molecule just as atoms absorb or emit light energy that corresponds to the energy of an electronic transition in the atom”. To summarize this, the amount of absorbance at a particular wavelength is proportional to its concentration. The objectives and overall purpose of this lab were to be able to produce data from the following procedures. To learn how visible and UV absorbance is related to its concentration, how to use a UV-visible spectrophometer, to prepare and utilize a calibration curve based on the Beer-Lambert Law, and to learn about oxidation of less active metals and complex ion formation. However, the major objective is to experimentally determine the amount of copper in a penny using the absorbance characteristics of the complex ion Cu(NH 3 ) 4 2+. A hypothesis can be made about the actual amount of copper in a penny since congress has mandated that the amount of copper in a penny be 2.5% ever since 1982. Before 1982 all pennies were approximately 95% Copper and 5% Zinc. However, due to the increase in the price of metals like copper, the composition had to be changed in order for the value of production of a penny stayed under the face value of a penny. In order for the pennies to still keep their physical appearance, they penny is now made of zinc and coated with copper so as to retain color and texture Methods: 2
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Solution Preparation The experiment was conducted in three main steps. The first step, the preparation of the standard solutions, required that around 40mL of 5.00 g/L Cu 2+ be gathered from the TA in charge. After this was done, 6 50mL Volumetric Flasks were gathered in order for Cu
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