Percent of Cu in a post 1982 cent
PURPOSE: What is the experimental % of copper (Cu) in a post 1982 cent? In this lab, we will determine the % composition of a modern (post-1982) penny by using a strong acid called nitric acid (HNO3), to react and dissolve the zinc core, leaving only the copper coating. Once only copper remains, we will then compare its’ absorbency to the other five post-1982 penny Cu concentrations made in this lab.
INTRODUCTION: Before 1982 the US penny was made of pure copper. Because of the high cost of copper, the US government changed the composition of the penny. As of 1982, pennies have been made of mostly zinc, with a thin copper layer on the outside. The first step in finding the % of copper is to make solution out of the penny. In other words “liquefy” the penny. To differentiate between the copper and zinc; zinc is clear and copper turns blue. During this lab, we will be making several standard solutions of this penny solution. To find out each solutions concentration, we will find its molarity by using the formula:
Cc x Vc = CD x VD
Beer's Law states that the quantity of light absorbed by a substance dissolved in a non-absorbing solvent is directly proportional to the concentration of the substance and the path length of the light through the solution. In order to find the solutions absorbency, we must first use a spectrophotometer which is a machine for determining the ability of a solution to absorb light of a specific wavelength by measuring the transmitted light. This must be done first in order to find a solution’s absorbency. By using the standard solutions previously made, the absorbency of each concentration solution will help find the pennies % of copper in your post-1982 penny.
Equation for the reactions between the post-1982 penny and nitric acid:
Cu(s) + HNO3(aq) → Cu(NO3)2(aq) + NO2(g) + 2H2O(l) colorless Zn(s) + HNO3(aq) →