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

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.

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

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

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

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

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

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.

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.

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.

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

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

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 0 0 +2 -2 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

Write the Redox equation for the copper plated screws Iron is being oxidized, Copper is being reduced Fe + CuCl2  Cu + FeCl2 0 +2 -2 0 +2 -2 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.

Write the REDOX equation for the iron and hydrogen gas Iron is being oxidized, Copper is being reduced Fe + 2HCl  H2 + FeCl2 0 2+ 2- 0 2+ 2- Fe  Fe2+ + 2e-[O] Oxidizing half-reaction 2H+ + 2e-  H2 [R] Reduction half-reaction 2H+ + Fe  H2 + Fe2+ Complete REDOX equation

References Copper Caper https://www.exploratorium.edu/science_explorer/copper_caper.html Clean Pennies with Vinegar http://www.sciencebob.com/experiments/pennychem.php Shiny Pennies http://www.elmhurst.edu/~chm/demos/ShinyPennies.html

Thank-You