Electroplating is a plating process in which metal ions in a solution are moved by an electric field to coat an electrode. The process uses electrical current to reduce cations of a desired material from a solution and coat a conductive object with a thin layer of the material, such as a metal. Electroplating is primarily used for depositing a layer of material to bestow a desired property (e.g., abrasion and wear resistance, corrosion protection, lubricity, aesthetic qualities, etc.) to a surface that otherwise lacks that property. Another application uses electroplating to build up thickness on undersized parts. The process used in electroplating is called electrodeposition. It is analogous to a galvanic cell acting in reverse. The part to be plated is the cathode of the circuit. In one technique, theanode is made of the metal to be plated on the part. Both components are immersed in asolution called an electrolyte containing one or more dissolved metal salts as well as otherions that permit the flow of electricity. A power supply supplies a direct current to the anode, oxidizing the metal atoms that comprise it and allowing them to dissolve in the solution. At the cathode, the dissolved metal ions in the electrolyte solution are reduced at the interface between the solution and the cathode, such that they "plate out" onto the cathode. The rate at which the anode is dissolved is equal to the rate at which the cathode is plated, vis-a-vis the current flowing through the circuit. In this manner, the ions in the electrolyte bath are continuously replenished by the anode. Other electroplating processes may use a non-consumable anode such as lead. In these techniques, ions of the metal to be plated must be periodically replenished in the bath as they are drawn out of the solution. The most common form of electroplating is used for creating coins such as pennies, which are small zinc plates covered in a layer of copper HE CHEMISTRY OF COPPER PLATING
This experiment demonstrates the process of electroplating and a commercial method used to purify copper. DESCRIPTION
This experiment is most appropriate for a first-year college prep or AP class if done quantitatively. If done qualitatively, it would be appropriate for a general class. One of the most important applications of electrolytic cells is the process of electroplating, in which a thin layer of metal is deposited on an electrically conducting surface. In electroplating, the metal to be plated is used as the anode and the electrolytic solution contains an ion derived from that metal. In this experiment, a copper anode (US penny) will be used in a solution of copper sulfate. Copper will be plated out onto a second penny at the cathode. TIME REQUIRED
30 minutes to set up; one period to complete.
electrolyte solution (200 g CuSO4· 5H2O + 25.0 mL concentrated H2SO4 solution in enough distilled or deionized water to make l.00 L of solution)* pre-1983 pennies
power supply (6.0-9.0 volts, 0.60-1.0 amps)*
connecting wires with alligator clips
16-18 gauge copper wire
cardboard square (approx. 15 cm on a side)
Sulfuric acid can cause severe burns; handle with care. Goggles must be worn throughout this experiment. Although the power source is relatively weak, the electrodes and connecting wires should not be handled when the cell is operating. If a 9-V battery is used as the power source, it will become quite hot during use; caution should be exercised. MODIFICATIONS/SUBSTITUTIONS
1. Copper(II) sulfate pentahydrate is available from garden supply stores as root eater. 2. Sulfuric acid is available from auto supply stores as battery acid. Substitute 95 mL of battery acid for 25 mL of concentrated sulfuric acid. 3. A battery charger or 9-V battery may be...