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 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 your NAME and HOUR.
2. Obtain a penny dated 1982 or later. Wash the penny with soap and water to get it clean.
3. Using a triangular file to make FOUR oppositely-placed small grooves into the edge of the penny (the marks with be approximately 90 degrees apart. The grooves must be deep enough so that the zinc is exposed, but not so deep that the penny's mass is greatly affected. Your markings should be placed near the bolded dashes like so
4. Clean the top and bottom surface of the penny with steel wool until it’s shiny. Rinse the penny in acetone and dry it on paper towel.
5. Determine the mass of the penny on the balance, and record the mass in the table on the bottom of the page. Removed the penny from the balance using tweezers and place it in its beaker.
6. While wearing gloves, carefully pour 50 mL 3M HCl into the beaker.
7. Place your labeled beaker under the fume hood to react overnight. Observe the effect the acid has on the copper outside of the penny.
8. Make a prediction in the table below on the percent copper and percent zinc