The first demonstration - Plating a copper penny with Zinc

For the first demonstration, the cathode will be copper (pennies), the anode will be zinc, and the "electrolyte" (the solution) will be zinc dissolved in vinegar and water. Zinc anodes are available from boating stores.

With a hacksaw a teacher or the group can cut many slices from one anode.

A second option to obtain zinc is to sand down a modern U.S. penny (1983 or later) until the copper surface is removed and the underlying zinc core is exposed. This source of zinc lacks some elegance, though, because it removes a little bit of the magic by showing that the penny was already electroplated, and it tends to be confusing, with some pennies zinc colored because of sanding before you even start the electroplating.

Note: A third possible source of zinc is the shell of conventional carbon-zinc batteries (make sure not to use alkaline batteries like Duracell or Eveready Energizers, nor rechargeable nickel-cadmium batteries -- just the cheapest 1-1/2 volt AA, C, or D plain carbon-zinc batteries). The science teacher can cut up such batteries and remove the black glop, and give the student the cleaned zinc strip.

For the pennies that you wish to plate onto, although any pennies will do, if you start with a dull brown penny, you'll end up with a dull zinc plated penny. Try to find shiny new pennies for best results! Immediately before plating, clean the penny with toothbrush and toothpaste; an even better cleaner, if you have it, would be Bon-Ami [link is to product info at Amazon]. Rinse well after cleaning. Your hands are oily, so wear plastic gloves so you do not get fingerprints or other soils on the penny after you clean it.

A transparent plating container is best, a Pyrex beaker is excellent, but a glass dessert bowl can serve well.

A recipe for the solution, suggested by Tom Pullizzi, and found to work is:

1). Fill the container about half way with vinegar (vinegar is mild acetic acid).

2). Put the zinc anode into vinegar and let it sit for several hours, allowing some of the zinc to dissolve.

3) Add 100 g/l of Epsom Salt [link is to product info at Amazon] (this makes the solution conductive; table salt will work fine, too, but is a little less safe because if students get carried away and start using really high voltages, table salt can generate chlorine gas, whereas Epsom Salt, magnesium sulphate, can't).

4) Add 120 g/l of table sugar. This is called a "brightener", and it's function is to sort of interfere with crystal growth, causing more and smaller crystals for a brighter, harder, plating.

5). Connect one flashlight battery (1-1/2 volts) to the penny and the zinc anode, and place them into the solution. Don't let them touch each other.

With luck, within a few minutes you'll begin to get a bright silvery coating. Ted Mooney didn't have quite that much luck when he tried it, but did find that a reapplication of the toothbrush and Bon-Ami quickly polished the thin greyish coating he got to a fairly bright shine.

Date: 2016-04-22; view: 760