Determination of Percent Composition of Pennies Using Redox and Double Displacement (Precipitation) Reactions
Objectives: The lab experiment will consist of oxidation-reduction and double displacement reactions as well as titration techniques. All these components will be used in order to determine the percent composition of pennies. In conducting redox and double displacement we are able to analyze a penny and figure out the chemical composition of the product. The experiment entails careful observations and recording of evidence for a chemical reaction. In this experiment observe gases being produced, the forming of precipitation and color changes.
1. What is the weight of a post 1982 penny?
- Approximately 2.496 grams
2. What is the percent copper and zinc in a post 1982 penny?
- 97.5 % Zinc and 2.5 % Copper
3. How many grams of copper and zinc are in a post 1982 penny?
- (2.496 x 0.975) = 2.43 g of Zinc (2.496 x 0.025) = 0.062 g of Copper
4. How many moles of copper and zinc are in post 1982 pennies?
(2.43 g Zn x 1 mol Zn) / 63.38 g Zn = 0.037 mol Zn
(0.062 g Cu x 1 mol Cu) / 63.54 g Cu = 0.00097 mol Cu
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?
(2.43 g Zn x 1 mol) / 65.38 g Zn = 0.037 mol Zn
(0.037 mol Zn x 2mol HCl) / 1 mol Zn = 0.074 mol HCl is needed
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?
- (0.074 mol HCl / 0.05 L) = 1.48 M
8. In the scenario described in