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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

1. Mix 45 - 50g copper chloride with 1500 mL of water in a tall (2 L) graduated cylinder.

2. Cut a strip from an aluminum pie pan. Twist into an interesting shape.

3. Place the aluminum in the copper chloride solution.

4. 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

• During this reaction, three observations of a chemical reaction may be made:
  1. The copper chloride solution changes color from green-blue to almost colorless;
  2. The reaction evolves heat;
  3. 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

1. Identify three changes to indicate that this is a chemical reaction.

2. What change has taken place in the copper atoms that reacted?

3. What change has taken place in the aluminum atoms?

4. Will any other metal react in a similar way when placed in a solution of copper chloride?