1. Shiny Penny Experiment
Chemistry 3202 Unit 4: Electrochemistry
By Whitney Pye and Jessica Simms

2. Introduction Why are the pennies Dirty?
Pennies get dull and dirty because the copper in the pennies reacts with oxygen in the air to form copper(II) oxide.

3. Experiment Materials: Four Beakers or cups containing:
Beaker 1: 5 ml soap and 60 ml water
Beaker 2: 60 ml Vinegar
Beaker 3: 5 ml salt and 60 ml water
Beaker 4: 5 ml water and 60 ml vinegar
About 40 pennies (10 for each beaker
2-3 steel screws

4. Hypotheses
Predict what will happen to the pennies in each of the four beakers
Beaker 1: Soap and Water
Beaker 2: Vinegar  
Beaker 3: Salt and Water
Beaker 4: Vinegar and Salt

5. Experiment
Place 10 pennies in each beaker/cup, stir and let sit for about 5 minutes

6. Results
What did you observe? Which of the solutions “cleaned” the pennies the best?
Beaker 1: Soap and Water
Beaker 2: Vinegar
Beaker 3: Salt and Water
Beaker 4: Vinegar and Salt
Explain your observations

7. Write the balanced equation for the penny reaction
+ NaCl  (vinegar) + (salt) 
HC2H3O2
HCl + NaCH3O2 (hydrochloric acid) + (sodium acetate)
CuO + HCl --->
copper(II) oxide + hydrochloric acid --->
CuCl2 + H2O copper(II) chloride + water

8. Part 2: Adding the Screws
Remove the pennies from the beaker containing the vinegar and salt.
Take the screws and place them into the beaker containing the vinegar and salt solution.
Try to place them so that at least one of the screws is only partly submerged in the solution.
Take note of any activity or changes in the beaker.

9. What is happening to the screws
When you put your dirty pennies in the vinegar and salt, the copper oxide is dissolved releasing copper ions into solution.
Steel is a metal made by combining iron, other metals, and carbon. When you put the steel screws in the mixture, some of the iron is oxidized into iron ions. As a result the copper (II) ions are reduced and form a copper plating on the screw.

10. What other observations did you notice when the screws were added to the solution?
Why did bubbles come off the steel screw?
Each water molecule is made up of two hydrogen atoms and an oxygen atom. In an acid, lots of hydrogen ions are floating around. In the chemical reactions at the surface of the screw, some of these hydrogen ions join and form hydrogen gas. The bubbles that you see coming off the screw are made of hydrogen gas.

11. REDOX (Reduction and Oxidation)
REDOX occurs when there is a transfer of electrons
from an ion
 OIL RIG – Oxidation involves loss, Reduction involves gain
A REDOX equation is the sum of a an oxidation half-reaction
and a reduction half-reaction
Can only occur in single replacement reactions

12. REDOX The species being oxidized, the species being reduced,
the oxidizing agent and the reducing agent only apply to reactants
in an equation
They have dual roles:
eg. The species being oxidized is losing electrons,
and is also the reducing agent

13. Redox Equation for the formation of copper oxide
Copper is being oxidized and the oxygen is being reduced
 Copper is the species being oxidized and the reducing agent
2Cu + O2  2CuO
Oxidizing numbers can be found
on the periodic table or online
Cu  Cu2+ + 2e- [O] Oxidizing half-reaction
O2 + 4e-  2O2- [R] Reduction half-reaction
2Cu + O2  2CuO Complete REDOX equation

14. Write the Redox equation for the copper plated screws
Iron is being oxidized, Copper is being reduced
Fe + CuCl2  Cu + FeCl2
Fe  Fe2+ + 2e- [O] Oxidizing half-reaction
Cu2+ + 2e-  Cu [R] Reduction half-reaction
Cu2+ + Fe  Cu + Fe2+ Complete REDOX equation
Cl2 is a spectator ion, so does not show up in the REDOX equation.

15. Write the REDOX equation for the iron and hydrogen gas
Iron is being oxidized, Copper is being reduced
Fe + 2HCl  H2 + FeCl2
Fe  Fe2+ + 2e-[O] Oxidizing half-reaction
2H+ + 2e-  H2 [R] Reduction half-reaction
2H+ + Fe  H2 + Fe Complete REDOX equation

16. References Copper Caper
Clean Pennies with Vinegar
Shiny Pennies

17. Thank-You