CHM144 Lab 8 Lab Report FINAL - Finding the Amount of...

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Finding the Amount of Copper in PenniesSamantha StretarPartners: Alexandra Swartz and Brenton SullivanMichelle Veite, Professor Yasmin Jessa, CHM144D, 11/13/14IntroductionStrong oxidizing agents are needed to oxidize copper.Nitric acid is an example of astrong oxidizing agent that has the ability to oxidize less active metals including Cu.Thebalanced equation of the oxidization reaction between Cu and HNO3is:Cu (s) + 4HNO3(aq) + 2H2O (l) Cu(H2O)42+(aq) + 2NO2(g) + 2NO3-(aq)Copper is present in pennies along with zinc.When Zn is oxidized by HNO3thefollowing reaction occurs:Zn (s) + 4HNO3(aq) + 2H2O (l)Zn(H2O)42+(aq) + 2NO2(g) + 2NO3-(aq)The oxidation reactions of Cu and Zn produce complex ions of Cu(H2O)42+andZn(H2O)42+.The central metal ions, Cu2+and Zn2+, are covalently bonded to the neutralmolecular ligands H2O.These H2O ligands can be displaced by ammonia to create two newcomplex ions:Cu(H2O)42+(aq) + 4NH3(aq)Cu(NH3)42+(aq) + 4H2O (l)Zn(H2O)42+(aq) + 4NH3(aq)Zn(NH3)42+(aq) + 4H2O (l)Formation of the new Cu(NH3)42+ion creates a deep blue color because the ion absorbsred light.The blue color allows for the determination of the concentration of Cu without conflictof the concentration of Zn.Therefore, aqueous NH3is an effective additive to determine theconcentration of Cu in a penny.The concentration of a compound in a solution is directly proportional to the amount oflight energy absorbed by that compound in the solution at a particular wavelength.A UV-visiblespectrometer is able to measure the amount of light energy absorbed at a particular wavelengthfor the Cu(NH3)42+ion.The main objective of the experiment was to determine the amount of copper present in apenny.Another objective was to determine if there was a relationship between the Cu contentand the age and condition of the coin.1
The hypothesis tested was that the percentage of copper present in a penny is around2.5% by mass based off of Congressional mandate.Various factors could affect the percentageof copper present in a penny such as the age and condition of the penny sample.Most of thecopper in a penny is present on the outer surface, so wear and tear over multiple years could leadto erosion on the surface and therefore a decrease in the % of Cu present in a penny.MethodsI.Preparation of the Standard Solutions and Penny SamplesForty milliliters of 5.00 g/L stock Cu2+solution was measured using a clean beaker.Six, 50-mL volumetric flasks were obtained and cleaned.The stock Cu2+solution, in volumes of 0.00mL, 2.00 mL, 4.00 mL, 6.00 mL, 8.00 mL, and 10.00 mL, was pipetted into the separatevolumetric flasks.

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Term
Fall
Professor
STEWART
Tags
Chemistry, Penny Samples

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