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Growing Copper Crystals (continued)
Results:
• When water is added to the salt layer, it will turn greenish as copper ions seep into the layer; this is a sign of a chemical change start-
ing to take place.
• The tips of the nails should start to turn reddish shortly after being inserted. It looks like rust but is actually fine powdery copper
forming as the single replacement reaction starts.
• As the replacement reaction continues, the copper will grow into a crystalline form and gain luster.
• As the copper sulfate crystals decrease, the copper metal crystals increase.
• The chemical equation for this experiment is "copper sulfate+iron copper+iron sulfate."
Teacher Notes:
• You can save lab time by pre-filling the preforms with the copper sulfate crystals. You could also clean the nails for the students.
• Be sure to use the correct nails. Galvanized nails will turn black from the zinc coating.
• The nails will eventually start to corrode. The amount of rust can be reduced by cleaning only the tips of the nails, and by not
stirring up the salt when they are embedded. You could also coat the tops of the nails with clear nail polish leaving the bottom ½"
or so exposed.
• Carefully adding the water in each step so as not to agitate the layers will also help minimize the amount of chloride ions in the
water around the nails.
• A yellowish fuzz may form in the water around the nails, which is most likely iron chloride.
• Once the copper sulfate crystals are gone, the copper crystals can be carefully removed from the tube and kept by the students.
• I have the students sketch their observations during the initial lab, the following day, and then a few days or even a week later.
• Tubes can be cleaned out and reused, but I usually just let the students take them home.
• When the reaction is complete, water can be filtered out into the sink and the solids can be disposed of in regular waste bins.
Extensions:
• Connection to geology, minerals, and mining
