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Aluminum - Copper Tradeoff
A tall cylinder of green-blue copper chloride solution and a strip of aluminum react to produce changes in colors and temperature, with formation of a solid.
Materials
- Copper(II) chloride, CuCl2, crystals.
- Aluminum pie plate; foil is too light & will disintegrate during the reaction.
- Bench liner
- paper towels
- Parafilm
- gloves.
Procedure
- Mix 45 - 50g copper chloride with 1500 mL of water in a tall (2 L) graduated cylinder.
- Cut a strip from an aluminum pie pan. Twist into an interesting shape.
- Place the aluminum in the copper chloride solution.
- Observe and identify as many changes as possible.
Reaction
This demonstration is a replacement reaction in which the more active metal, aluminum, replaces the copper ions in solution.
2Al(s) + 3Cu2+ (aq) --> 2Al3+ (aq) + 3Cu(s)Teaching Tips
NOTES
- During this reaction, three observations of a chemical reaction may be made:
- The copper chloride solution changes color from green-blue to almost colorless;
- The reaction evolves heat;
- A new colored solid forms.
- Encourage students to write their observations. Help them to avoid saying that the aluminum "turned to a new substance" or that it "rusted."
- The spongy copper that forms on the surface of the aluminum can be identified bacause it will not react with hydrochloric acid.
- The spongy copper can be fused by a hot flame to form the more recognizable metallic copper. Take the copper to a welding facility.
QUESTIONS FOR STUDENTS
(from Summerlin, L.R., C.L. Borgford and J. B. Ealy, Chemical Demonstrations - A Sourcebook for Teachers, Volume 2, American Chemical Society, Washington, D.C., 1987.
- Identify three changes to indicate that this is a chemical reaction.
- What change has taken place in the copper atoms that reacted?
- What change has taken place in the aluminum atoms?
- Will any other metal react in a similar way when placed in a solution of copper chloride?
