prelab 8

Topics: Chemistry, Solubility, Chemical reaction Pages: 3 (564 words) Published: November 16, 2014
DETERMINATION OF % COMPOSITION OF PENNIES USING REDOX AND DOUBLE DISPLACEMENT (PRECIPITATION) REACTIONS Pre- Lab 8
Objective: The purpose of this experiment is to determine the percent composition of pennies using oxidation-reduction and double displacement reactions as well as titration techniques. We will take a post 1982 penny and place in a strong acid dissolving the zinc core and leaving behind the copper coating. We will figure out the percent composition from the mass of copper and zinc using titration and precipitation. Procedure:

1) First dissolve the zinc core of a penny and leave copper covering intact by applying four notches in the coin using a triangular file. 2) Place the penny in a 50 mL of a pre-determined concentration of HCl solution overnight. 3) Then determine the percent copper from the mass of copper. 4) Find the percent of zinc by precipitation and titration

5) If there is a known amount of HCl added to the beaker that penny is placed in, then determine the amount of HCl that was used up in the reaction of HCl and Zinc. Calculate the % of zinc in penny. 6) If zinc reacts with NaOH in the titration experiment, then zinc hydroxide will form. Check solubility rules to see if zinc hydroxide is soluble of insoluble. Then calculate for % zinc in penny.

Questions:
1. What is the weight of a post 1982 penny? 2.5 grams
2. What is the percent copper and zinc in a post 1982 penny? 97.5% Zn and 2.5% Cu 3. How many grams of copper and zinc are in a post 1982 penny? (2.5)(.025)= 0.0625 grams of Copper and (2.5)(.975)= 2.4375 grams of Zinc

4. 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?

7. In a procedure developed to determine the percent zinc in post 1982 pennies, 50 ml of an HCl solution was used to react...
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