OBJECTIVES:

• Exploring how elements can be released from compounds.
• Experimenting with electroplating.

VOCABULARY:

• anode
• cathode
• electrode
• ion
• solute
• solvent

MATERIALS:

• beakers
• Rock Cycle - Chemistry (6) 
• Electricity Kit  (2 sets)
• 6 volt set up

Students set up and use an electroplating apparatus.

Copper ore

BACKGROUND:

An atom consists of three basic components: electrons, protons, and neutrons. An electron has a negative charge; a proton has a positive charge; a neutron has no charge. An atom that has a charge is called an "ion." If an ion has too many electrons, it has a negative charge. If an ion has too many protons ( not enough electrons) it has a positive charge. Positive and negative ions will combine to form neutral substances.

When a solute is dissolved in a solvent, the compound is "broken" into its consistent atoms, which are almost always ions. These ions will easily be attracted to other ions if given the chance. Positively charged ions will be attracted to negatively charge ions.

In this lab, the students will experiment with the bonding behavior of elements through electroplating (the art of producing metallic coatings by using electric currents.) Economically, metallic coatings are used to improve appearance, resist corrosion, or improve hardness. Examples include plating steel with copper, nickel, or chromium in the automotive industry; tin plated steel for food cans; and the manufacture of silver or gold plated jewelry.

In this lab, the students will make a solution of copper sulfate in water. When water is added to the copper sulfate, the copper sulfate is broken into copper ions (Cu²⁺) and sulfate ions (SO₄^2-). The copper ions roam around in the solution looking for a negatively charged with which to combine.

This process is facilitated by passing an electric current through the solution. In this lab, the power source is a battery. As directed below, a copper strip is wired to the battery’s positive terminal (the anode), while a zinc or iron strip is attached to the negative terminal (the cathode). When electricity flows through the circuit, the positive copper ions in solution bond to the negatively charged metal. In addition, the copper strip loses Cu²⁺ ions, which replace the Cu²⁺ ions lost from the solution. Given time to experiment, any substance can eventually be electroplated. Students will see that elements can "move" around with just a small amount of energy from the battery.

PROCEDURE:

1. Reinforce to students that chemical compounds are made of elements, which are composed of atoms. This lab will demonstrate how elements by becoming ions can be manipulated and moved from one area and deposited in another. Emphasize that it is not magic when the elements move around, but their response to the electrical current.
     
2. Perform the electroplating experiment, following the directions below.
     
   1. Mix the solution. Use 250, 500, or 1000 ml glass beakers. For every 250 ml of water, use approximately 5 ml of copper sulfate. Copper sulfate is included in the kit.

      Note: After the experiment, you can safely dispose of the solution down the sink. However, the solution is reusable for a few years. If you keep it, store in it safe place, correctly marked as copper sulfate solution.
       

   2. Place the electroplating materials on a table. Make sure that the beakers and electrodes are clean. . Use alligator clips from the Electricity Kit to attach the battery to the copper and zinc strips that are included in the Rock Cycle - Chemistry (6) kit.
        
   3. Using the alligator clip, connect the wire wrapped to the piece of copper to the POSITIVE  battery terminal (see the diagram). Connect the other wire to the NEGATIVE battery terminal. You should now have one wire from the positive terminal connected to the copper electrode and one wire from the negative terminal connected to the iron or zinc electrode.
       
   4. Place the electrodes in the solution and let the experiment stand. You should begin to see little bubbles form on the copper electrode very soon. If you wire the electrodes backwards, a different reaction will occur; a black film will coat the electrode. If this happens, clean all the metal by wiping it with a tissue, and try the experiment again.
       
   5. Let the electrodes stay in solution for about 5 minutes. When removed, the anode (positive)  should be coated with copper.  You can replace the zinc strip with other metals and see what happens (i.e. nickel).  

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