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Electrolysis

Name of Corresponding Unit Plan: Artifact Conservation

Grade Level: 8-12

Common Core Standards:
RS.3. Follow precisely a complex multistep procedure when carrying out experiments.

Content Areas: Science

Recommended Length/Duration: Initially one 45-60 minute lesson, 5-10 minute daily observations, 30-60 minute summary of findings

Learning Goals: Students will observe the changes over time in an object treated through electrolysis.

Students will understand the electrochemical processes at work in electrolysis.

Description/Sequence:

This experiment should follow a discussion on the chemistry of corrosion.  This will lead to the introduction of using the electrochemical process to remove rust from iron artifacts.

  1. Describe how electrical current in an electrolysis reaction causes ions from the cathode (reduction of metal to be treated) to flow through the electrolyte to the anode (oxidization of the sacrificial metal). Choose an artifact with obvious signs of rust.  Have student describe the object in detail and perhaps photograph it.
  2. Set up the electrolysis apparatus.  Point out the object to be treated (cathode) and the scrap iron to be oxidized (anode).  Suspend them without touching in an aquarium or large plastic bucket.  Use 1 tablespoon of Baking Soda per gallon of water, or a similar electrolyte, to cover the cathode and anode samples.  Attach securely a wire lead to teach sample. Use a laboratory rectifier or a battery charger to supply the direct current needed.  Connect the positive lead from the power source to the anode and the negative lead to the cathode.  Turn on the power source to a low setting (2 amps).  Bubbles around the cathode should appear in a few minutes.
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  4. Let the reaction run for several days.  Have students make observations at least once each day.
  5. Once the reaction has run its course, rinse off the object and have students describe its appearance in detail and perhaps photograph it. Discuss what changes have resulted from the electrolysis process. Guiding questions might include:
    • How has the condition of the metal changed?  Cathode?  Anode?
    • How long did the process take?
    • How might the conditions of the process be changed?  What would the result be?
    • Does electrolysis have any practical value in industry or everyday life?

Assessments: Informal assessment of student participation

Materials/Resources: Aquarium or large container for electrolyte, a rusty artifact and a piece of iron based scrap metal, Wire, Lab Rectifier or Battery Charger, Water and baking soda

Special Considerations: Safety precautions for using acids should be employed.  The byproduct gas of the reaction is hydrogen, so the experiment should be set up in a well ventilated room.

The time needed for the reaction will depend upon the size of the object and the extent of corrosion.  It may be a few hours or several days.

In some settings it may be best to unplug the electrical current during times when the reaction is unattended.

Extensions: This lesson is designed as a class demonstration primarily because of the specialized equipment needed.  If available, multiple samples could be treated under different conditions.

Students may want to “clean” personal objects from home.

Students may want to learn about other ways electrolysis is used in research and industry.

Further reading:

Removing Rust with Electrolysis, article by George Vondriska

Electrolytic Reduction for Iron Artifacts, video by Algonquin College Applied Museum Studies Conservation Department