Summary

In this lesson, students will consider the need for innovative solutions to e-waste both from an environmental perspective as well as for the economic benefit to reclaiming raw materials from used electronic devices. They will then take on the role of an electroplate technician who is tasked with evaluating the effectiveness of a copper recycling process that uses electrolysis to purify and recover copper metal from e-waste. As e-waste is a relatively new—and growing—issue, it demonstrates how new industries can develop that utilize skills from existing jobs.

Grade Level

High School

NGSS Alignment

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

• HS-PS1-7: Use mathematical representation to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.
• HS-ETS1-3: Evaluate a solution to a complex real-world problem based on prioritized criteria and trade-offs that account for a range of constraints, including cost, safety, reliability, and aesthetics as well as possible social, cultural, and environmental impacts.
• Scientific and Engineering Practices:
  • Using Mathematics and Computational Thinking
  • Analyzing and Interpreting Data
  • Obtaining, Evaluating, and Communicating Information

AP Chemistry Curriculum Framework

This lab supports the following unit, topics and learning objectives:

• Unit 4: Chemical Reactions
  • Topic 4.1: Introduction for Reactions
    • TRA-1.A: Identify evidence of chemical and physical changes in matter.
  • Topic 4.2: Net Ionic Equations
    • TRA-1.B: Represent changes in matter with a balanced chemical or net ionic equation: a. For physical changes. b. For given information about the identity of the reactants and/or product. c. For ions in a given chemical reaction.
  • Topic 4.7: Types of Chemical Reactions
    • TRA-2.A: Identify a reaction as acid-base, oxidation-reduction, or precipitation.
  • Topic 4.9: Oxidation-Reduction (Redox) Reactions
    • TRA-2.C: Represent a balanced redox reaction equation using half-reactions.
• Unit 9: Applications of Thermodynamics
  • Topic 9.7: Galvanic (Voltaic) and Electrolytic Cells
    • ENE-6.A: Explain the relationship between the physical components of an electrochemical cell and the overall operational principles of the cell.
  • Topic 9.10: Electrolysis and Faraday’s Law
    • ENE-6.D: Calculate the amount of charge flow based on changes in the amounts of reactants and products in an electrochemical cell.

Objectives

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

• Describe both the challenges and the opportunities presented by growing amounts of e-waste.
• Perform an electrolysis reaction to recover copper metal from a solution containing copper ions.
• Calculate the theoretical yield and experimental percent yield of copper recovered via electrolysis.
• Evaluate experimental data and suggest additional factors to consider when determining whether an electrolytic recycling process would be beneficial to add to an electroplating company’s portfolio of services.

Chemistry Topics

This lesson supports students’ understanding of:

• Redox reactions
• Electrolysis
• Molarity and ionic solutions
• Quantitative chemistry

Time

Teacher Preparation: 30 minutes for CuSO₄ electrolyte solution preparation
Lesson:

• Part 1: “E-Waste: Challenges and Opportunities”: 30-45 minutes (or assigned as homework)
• Part 2: “Recycling Copper from E-Waste”: 45-60 minutes

Materials (per lab group)

• 4-6 graphite pencil leads (5 to 9 mm; thicker leads are less prone to breakage)
• Lab or masking tape
• 3 wires with alligator clips
• 2 thermometer clamps and ring stand
• 6V or 9V alkaline battery
• 50 - 100 mL Copper sulfate electrolyte solution (1 M) per lab group
• 100-mL graduated cylinder
• 100-mL beaker
• 0.01-g balance (or more precise) and weighing paper

Optional:

If you do not have time or the materials below for each lab group, average current data can be provided to students instead of measuring the current at 1 minute intervals (see teacher notes)

• Ammeter and wire with alligator clip
• Timer (stopwatch or cell phone apps are suitable)

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.
• When working with acids and bases, if any solution gets on students’ skin, they should immediately alert you and thoroughly flush their skin with water.
• When diluting acids, always add acid to water.

Teacher Notes

• The National Science Board estimates that there are over 16 million jobs in the Skilled Technical Workforce (STW) that don’t require a 4-year college degree, but require STEM knowledge such as the use of chemicals, application of arithmetic and algebra, and the knowledge of quality control and other techniques for manufacturing goods. This lesson was developed as part of a content writing team to support the ACS Strategic Initiative on Fostering a Skilled Technical Workforce, with the goal of increasing awareness of and appreciation for STW opportunities in the chemistry enterprise at the high school level.
• This lesson plan introduces students to electrolysis and related electroplating jobs in the STW. Electroplaters use math and electrochemistry to coat plastic and metal products with metals such as zinc, nickel, copper, silver, and chromium. Surface coatings can be used to protect against corrosion, increase conductivity, or for aesthetic reasons. Electrolysis is also used purify metals such as copper. There are new applications for electrolysis in recycling of e-waste as well as production of hydrogen that will draw on the same skills.
• Note that, even though there are AP topics listed for this resource, the laboratory techniques used in this lesson could be completed by general chemistry students. However, they might need more detailed instruction on the relevant electrochemistry concepts and/or additional support with calculations than AP students. The math itself is not too complex, but the electrochemistry concepts might be unfamiliar and potentially intimidating.
• This lesson consists of two parts:
  • Part 1, “E-Waste: Challenges and Opportunities,” provides students with some background information on the growing problem of e-waste, as well as potential opportunities to convert e-waste into useable materials. This activity can be completed during class time and provide the basis for class or small-group discussion, or, if time is limited, could be assigned for homework ahead of the lab component.
  • Part 2, “Recycling Copper from E-Waste,” gives students the opportunity to assume the role of an electroplater who is has been asked to test out and evaluate a process that uses electrolysis to recover copper from e-waste. This utilizes several skills that are needed in the STW, including operating technical equipment, collecting and analyzing data, and considering improvements and costs for industrial processes.
    • Students will likely only have time to run one trial of the lab procedure, so you could have them pool their data in a shared document if you want them to have access to multiple data sets.
    • Students are guided through the electrochemistry calculations – the structure of each calculation is provided and students simply plug in the measurements they took in the lab. To increase the level of difficulty (particularly for honors/AP students) this scaffolded approach can be removed from the student document, and additional questions about net ionic equations could be added.
• All schematic diagrams in the teacher and student documents were made with Chemix, a free online tool for creating scientific lab diagrams.

Electrochemistry Resources

• Ideally, students should be familiar with the terms and units used in electrochemistry (including solutions-related topics like molarity), though they are provided with the basics in the reading sections of the lab document. How a battery works from the Australian Academy of Science is a useful primer on units and definitions related to batteries.
• If students are unfamiliar with electrolysis or need to review the process, use the Greenbowe and Gelder “Electrolysis” simulation to illustrate electron flow and redox reactions. AACT has a related simulation showing half reactions and electron flow in galvanic, or voltaic, cells, where electrons flow in the reverse direction compared to electrolytic cells.
• This resource provides detailed descriptions with diagrams of an electrolytic cell for copper sulfate using inert electrodes (as described in this lesson), as well as an alternative set up using copper electrodes. There are also examples of practical industrial applications of electroplating using various types of metals that could be shared with students.

Experimental Setup

• You will want to build a demo apparatus for students to refer to as they assemble their cells:

• The two half-reactions listed below occur in the electrolytic cell. Students should observe that reddish-brown copper metal forms at the cathode, and bubbles form at the anode due to the presence of oxygen gas as a product of that half-reaction. You could also show this video to give students a preview of what they can expect to occur at each electrode.

Battery

• Either 6V lantern batteries or 9V batteries work well for this activity and can be connected directly to the electrodes with alligator clips. Other alkaline cells won’t produce sufficient current.
• Ideally, the cell should be run for at least 20 minutes (longer if possible) to obtain enough copper that can be measured to 2 significant figures on a 0.01-g balance. (20 minutes with an average current of 260 mA and a 1 M CuSO₄ solution should yield about 0.11 g of copper.)
• Keep track of how long each battery has been used so that it doesn’t die mid-experiment. A typical 6V battery has a rated capacity of 10,000 mAh with a 500 mA discharge and can probably be used for 20 hours total without failure.

Electrolyte

• For best conductivity and control of the anode reaction, use copper sulfate solution (between 0.5 and 1 M CuSO₄), in dilute (0.5 to 1 M) H₂SO₄. The sulfuric acid is necessary to maintain solution conductivity as the reaction progresses. To prepare 500 mL of 1 M solution (enough for 10 trials), add 124.84 g of CuSO₄ · 5 H₂O to a 500 mL volumetric flask and dissolve in 0.5 M H₂SO₄.
• Alternatively, you can purchase copper (II) sulfate electrolyte solutions (estimated 0.8 M CuSO₄ and 0.6 M H₂SO₄) from Flinn Scientific or other sources. Be sure it is labeled Copper (II) Sulfate Electrolyte Solution and contains H₂SO₄.

Electrodes

• Mechanical pencil leads labeled high-polymer or HB are suitable as inert graphite electrodes. These leads are readily available in different diameters, but the thicker 9 mm leads are preferred for their greater durability. For convenience and greater surface area, use a small piece of tape to bundle 2-3 leads together for each electrode. Attach the alligator clips to the electrodes and support them over the beaker using thermometer clamps on a ring stand, as shown below.

• The copper that deposits on the cathode may be uneven and flaky; in the industrial process, there is greater control of current to allow even deposition. Instruct students to remove the cathode, carefully blot it on a paper towel, and allow to air dry before measuring the mass (potentially the next day to allow sufficient time for it to dry). Rinsing is not recommended as it may dislodge the copper.
• Pictured below for reference are samples of copper deposits on cathodes connected to 6V and 9V batteries for 15 minutes and 10 minutes, respectively. (Keep in mind that students should let the reaction continue for at least 20 minutes, longer if time allows.)

Percent Yield

• To calculate the yield of the process, it is necessary to know the current of the system. Students are instructed to measure the current every minute during the electrolysis with a multimeter or ammeter connected in series; that is, the device is a “wire” in the overall circuit as illustrated below. If the current shows as a negative value, just reverse the connections at the terminals.

• If equipment and/or time is limited, omit the measuring of the current from the student lab and instead provide representative current values from teacher set-up. Representative current for a 6V battery is 250 mA. If you will provide this to students, update the student document to remove the ammeter and instructions to record current.
• Using the average current multiplied by time the current was applied only provides an estimate of total charge in coulombs supplied, as the current isn’t constant for the entire process. However, this estimation is close enough for this analysis. Pointing this out to students could be a good way to start a conversation about error analysis more broadly.

Extension Opportunities

• Students could explore in greater detail various chemical, mathematical, engineering, and other interdisciplinary topics that relate to the copper recovery procedure they used in the lab portion of this lesson. See the “Extension Opportunities” document available for download in the sidebar for extension activities related to experimental design, spectroscopic analysis, copper refining, calculus, and cost analysis.

Additional Resources

• Teaching Electrometallurgical Recycling of Metals from Waste Printed Circuit Board (WPCB) via Slurry Electrolysis using Benign Chemicals, Journal of Chemistry Education
• Copper and Antimony Recovery from Electronic Waste by Hydrometallurgical and Electrochemical Techniques, ACS Omega
• FuseSchool Videos on “Purifying Copper” and “What is Electrolysis”
• Recycled Cell Phones--A Treasure Trove of Valuable Metals, the U.S. Geological Survey
  • Be aware that this is from 2006 and doesn’t represent the current generation of smartphones. This is the source of the figures cited on the EPA website.
• UN Report: Time to seize opportunity, tackle challenge of e-waste
• This video shows electrolysis processes of copper using inert graphite electrodes. Be aware that since the electrolyte in the video is not acidified, a different oxidation reaction for water occurs than in the experiment that is the subject of this lesson. The latter part of the video clearly illustrates electrowinning in copper refining.
• What Does an Electroplater Do?
• Certified Electroplater-Finisher course outline, National Association for Surface Metal Finishing