Indicating Electrolysis

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Electrolysis is the breakdown of water into hydrogen and oxygen. This Exploratorium activity allows learners to visualize the process with an acid-based indicator. This activity also has helpful videos to help you.

Quick Guide

Preparation Time:
10 to 30 minutes

Learning Time:
10 to 30 minutes

Estimated Materials Cost:
$1 - $5 per student

Age Range:
Ages 8 - 18

Resource Types:
Activity, Experiment/Lab Activity


Materials List (per student)

  • Two stainless steel screws, each at least 1.5 inches (40 millimeters) long (available at your local hardware store)
  • Shallow clear glass or plastic container such as a Petri dish
  • Epsom salts (available at your local drugstore) CAUTION: don't substitute table salt for this activity because it can produce chlorine gas
  • 9-volt battery
  • Rubber bands
  • Acid-base indicator such as phenol red, phenolphthalein, bromothymol blue, or cabbage juice indicator (see the Going Further section below for instructions on how to make your own)—make sure you’re aware of any safety issues and that you know which colors indicate acid and/or base when using your chosen indicator
  • Safety goggles
  • Spoon
  • Optional: magnets


  • Engineering and Technology
    • Engineering
  • Physical Sciences
    • Electricity and Magnetism
      • Electric Charges and Currents
    • Chemistry
      • Chemical Bonding
      • Acids and Bases
  • The Nature of Technology
    • The Design Process


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Access Rights:

  • Free access