Summary

In this lab, students will investigate oxidation-reduction reactions while creating a complex picture using reactions of copper solutions on aluminum foil. Students will also apply previous knowledge of reaction rate to adjust concentrations, allowing for artistic expression such as shadowing and layering in their artwork. 

Grade Level

High School

NGSS Alignment

This lab will help prepare your students to meet the performance expectations in the following standards:

• HS-PS1-5: Apply scientific principles and evidence to provide an explanation about the effects of changing the temperature or concentration of the reacting particles on the rate at which a reaction occurs.
• Scientific and Engineering Practices:
  • Analyzing and Interpreting Data
  • Planning and Carrying Out Investigations

Objectives

By the end of this lab, students should be able to:

• Dilute solutions to alter the rate of an oxidation reaction.
• Write half-reactions for oxidation and reduction reactions.
• Describe how changes to the solutions (such as molarity) will impact their design.

Chemistry Topics

This lab supports students’ understanding of:

• Redox Reactions
• Oxidation
• Reduction
• Half Reactions
• Reaction Rate

Time

Teacher Preparation: ~20 minutes
Lesson: ~1 hour

Materials

• 10cm x 10cm squares of aluminum foil (4-5 pieces per student)
• 0.5 - 1.0 M copper (II) chloride solution in bottle (pairs of students can share)
• 0.5 - 1.0 M copper (II) sulfate solution in bottle
• Application tools for solutions (toothpicks, cotton swabs, eye droppers, etc.)
• Empty containers (optional—for students to make diluted solutions if permitted)
• Distilled water
• NaCl solution (optional)

Safety

• Always wear safety goggles when handling chemicals in the lab.
• Students should wash their hands thoroughly before leaving the lab.
• When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.
• Gloves can be worn when handling copper solutions.
• For safe handling, refer to the SDS for SDS copper (II) chloride.
• For safe handling, refer to the SDS for copper (II) sulfate.

Teacher Notes

Helpful Background Information:

• Copper ions react with the aluminum in the foil in a standard oxidation-reduction reaction according to the equation below:

• As the aluminum is oxidized, the aluminum turns a dark brown color.
• There are additional reactions that occur that may be discussed to explain various student observations:
• Copper (II) ions will hydrolyze to produce an excess of hydrogen ions, making the copper (II) chloride solution slightly acidic:

• The reaction is also accompanied by the evolution of hydrogen gas:

• If students attempt to use copper sulfate, they will not see a reaction. Aluminum does not react with the solution of copper sulfate, as its surface is protected with a durable oxide film. If students are permitted to also experiment with additional NaCl, the Chloride ions necessary to remove the oxide layer, will allow a reaction to occur.

Implementation Tips:

• I recommend taking a somewhat hands-off teaching approach to this investigation. I like to present the students with the task and the tools, then explain the rubric guidelines. I let them experimentally determine how to increase or decrease the rate of the reaction.
• If evaluating the artwork, teachers must do so before they are taped to the final submission paper. By holding the creation up to the light, you will most likely see small pinholes. Additionally, the red/brown residue will easily rub off, so it is best to evaluate them immediately upon completion.
• If students become frustrated by the diluted solution slowing the reaction (and pinholes still occur), I offer a hint: If the Aluminum is too thin, there are two things you could do: The first is to dilute the copper solution, and the second is ____. Usually, students respond with, “strengthen the Aluminum?” I then remind them that they can use as many pieces of aluminum as they need (within reason). They realize that there are no longer holes after placing a fresh piece of aluminum behind their image. This allows them to focus on making impressive, intricate drawings.

Classroom Management Tips:

• To increase quantitative analysis, task students with calculating the molarity for any diluted solutions they make with the correct molarity (and labeling the bottles). This will also decrease waste as future lab groups could use those solutions instead of making their own.

Differentiation:

• The questions can be modified based on student ability, understanding and motivation.
• I suggest that teachers ask more leading questions to struggling students, such as, “I see you are frustrated that the Q-tip keeps rubbing off the reaction product. Is there another tool you could use that doesn’t actually touch the foil?” Similarly, ask open-ended questions to students who are advanced, such as, “I can tell you have made a house. Can you add shadows? A sunset?”

Expected results and assessment:

• I’ve provided an example rubric guide for teachers to demonstrate how a range of grades can be assigned based on discretion.

• Below are examples of student work. The left is a simple picture with clear margins, which would receive an average score (3) from the rubric above. The example on the right is an intricate picture with obvious control over the strength of reaction, which would receive a higher score (5) from the rubric above.