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 …show more content…
Pennies that have been made after 1982 are a composite of zinc and copper. The copper is plated on top of the zinc. What if we could reverse this composite by placing the zinc on top of the copper? The zinc can be removed from the penny by cutting the coin and creating a reaction between the zinc and the concentrated hydrochloric acid:
Zn(s) + HCl(aq) -> Zn2+(aq) + Cl - (aq) + H2(g)
Copper does not react with hydrochloric acid. After removing the zinc, reweigh the penny and obtain the mass of copper that is present. The remaining copper can be plated with zinc and the brass alloy produced. This process entails first creating a reaction between zinc and 6M sodium hydroxide:
Zn(s) + 2 OH-(aq) -> ZnO22-(aq) + H2 (g)
mL of ZnCl2 | 10 mL | Moles of ZnCl2 | 0.10 mol | mL of NaOH | 18.5 mL | Mass of Zn(OH)2 | 0.741 g | Mass of Zn | 2.38 g |
Discussion: In this experiment the amount of zinc