Determination of % Composition of Pennies Using Spectroscopy Essay

621 WordsMay 3, 20143 Pages
Determination of % Composition of Pennies Using Redox and Double Displacement (Precipitation) Reactions Introduction: Oxidation involves the gain of electrons of hydrogen or the loss of oxygen or decrease in oxidation state. If zinc completely reacts with HCL, then the theoretical yield of copper should be equivalent to the actual yield. Purpose: In this lab, we will determine the percent composition of a modern (post-1982) penny by using a strong acid to react and dissolve the zinc core, leaving only the copper coating. Once only copper remains, we will compare its mass to the entire mass of the penny to determine how much of a penny is copper and how much is zinc. 1. Obtain one 50.0 mL beaker, and label the beaker with…show more content…
How many moles of copper and zinc are in post 1982 pennies? 5. Write a balanced reaction of zinc with HCl. Zn(s) + 2HCl(aq) --> ZnCl2(aq) + H2(g). 6. How many moles of HCl are needed to react completely with all of the zinc in a post 1982 penny? 2.5 7. In a procedure developed to determine the percent zinc in post 1982 pennies, 50 ml of an HCl solution was used to react (dissolve) all of the zinc in the penny. To ensure complete reaction, the solution contains twice as many moles of HCl that is actually needed. What concentration of HCl should be used? In the scenario described in problem 7, what is the amount (in moles) of excess (unreacted) HCl in solution? 9. How many moles of NaOH would be needed to completely react with all of the excess HCl determined in problem 8? 10. As described in problem 7, a procedure was developed to determine the percent zinc in post 1982 pennies. In that procedure 50 ml of an HCl was used to react (dissolve) all of the zinc in the penny. To ensure complete reaction, the solution contains twice as many moles of HCl that is actually needed. To determine the percent zinc in the penny, the excess (unreacted) HCl was titrated with NaOH. Determine the concentration of NaOH needed if you want to use approximately 25 mL of NaOH to titrate the excess HCl. 11. Write the balanced chemical reaction of zinc with HCl (same as problem 5). Is the product of