Composition of Penny Using Redox Reactions Essay

1165 Words Apr 23rd, 2013 5 Pages
Determining the composition of pennies with redox reactions

The understanding of oxidation and reduction must be clear to carry out this lab. With the understanding of these concepts we can calculate or hypothesize for the properties of each element or compound. 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.
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
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Rinse the penny skin with distilled water and set it aside for a moment. Empty the solution in the beaker down the sinking with running water. Rinse out the beaker several times and gill it half full with distilled water.
10. Place the penny skin back into the beaker and allow it to soak in the distilled water for several minutes.
11. Using tweezers, remove the copper skin and allow it to air dry for 5 minutes.
12. Weigh the copper skin and record its mass in the table on the bottom of the page.

Mass of penny before(copper + zinc) | 2.4375 g | Prediction for % Cu | 0.076 g | Mass of penny after(copper only) | 0.0490 g | Prediction For % Zn | 0.304 g |

1. Calculate the mass of zinc reacted in the penny.
2. Calculate the percent Cu using the formula: %Cu= Final mass of the penny/Initial mass of the penny (100)
3. Calculate the percent Zinc using the formula:
%Zn = Mass of the zinc reacted/Initial mass of the penny (100)
4. Looking at the following equation for the reaction: Zn(s) + HCL(aq) + H2 + ZnCl2(aq)
Predict the missing product in the equation. What clue appeared in the penny/acid reaction beaker that would help verify this?
5. According to the United States Mint, pennies are 97.5% zinc and 2.5% copper, calculate the percent error in the lab using:
%error = Theoretical %Cu - Experimental %Cu/Theoretical %Cu (100)
6. Molar mass of Zn(OH)2 = 65.39+((15.99+1.007)x2) = 99.384

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