Old Foamey


Mix together hydrogen peroxide, sodium iodide solution and dishwashing liquid in a tall cylinder and stand back. Your students will observe with amazement a catalyst in action as an enormous amount of soapy foam erupts from “Old Foamey!”


  • Catalysts
  • Decomposition reactions


(for each demonstration)
Hydrogen peroxide, 30%, 20 mL*
Sodium iodide solution, 2 M, 5 mL*
Dishwashing liquid, 10 mL*
Food coloring (optional)
Graduated cylinders, 10- and 100-mL
Plastic tray, several inches deep
*Materials included in kit.

Safety Precautions

Hydrogen peroxide, 30%, will act as an oxidizing agent with practically any substance. This substance is severely corrosive to the skin, eyes and respiratory tract; a very strong oxidant; and a dangerous fire and explosion risk. Do not heat this substance. Sodium iodide is slightly toxic by ingestion. Although the dishwashing liquid is considered non-hazardous, do not ingest the material. Do not stand over the reaction; steam and oxygen are produced quickly. Wear appropriate chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. This activity requires the use of hazardous components and/or has the potential for hazardous reactions. Please review current Safety Data Sheets for additional safety, handling and disposal information.


The foam and solution left in the cylinder may be rinsed down the drain with excess water.


  1. Place a 100-mL graduated cylinder in a plastic tray that is several inches deep.
  2. Measure out 20 mL of the 30% hydrogen peroxide into the 100-mL graduated cylinder. Caution: Wear chemical resistant gloves and goggles when handling 30% hydrogen peroxide. Contact with skin may cause burns.
  3. Measure out 10 mL of dishwashing liquid into the 10-mL graduated cylinder and add it to the cylinder containing the hydrogen peroxide. Add a few drops of food coloring, if desired. Have your students observe that little or no reaction occurs.
  4. Measure out 5 mL of sodium iodide solution using the 10-mL graduated cylinder. Quickly but carefully, add the sodium iodide solution to the 100-mL graduated cylinder.
  5. Step back and observe the reaction.

Student Worksheet PDF


Teacher Tips

  • You may want to do this demonstration in the laboratory sink since there is a lot of foam produced. Cleanup, however, is easy due to the presence of extremely safe products and the generous amount of detergent.
  • The cylinder will get hot, so let it cool before handling.
  • This demonstration can be easily and safely scaled up for larger audiences. A 500-mL or 1-L Pyrex® graduated cylinder works well in this case. You may have heard of this demonstration also referred to as elephant toothpaste.
  • The slight brown tinge of the foam at the beginning is due to the presence of free iodine produced by the extreme oxidizing ability of the 30% hydrogen peroxide.
  • Another catalyst that will catalyze this reaction is manganese (IV) oxide, MnO2.
  • To demonstrate that oxygen is indeed one of the products, light a match and blow it out. Ideally, the center of the match will still be orange. Hold the match very close to the foam produced—the match should reignite.

Correlation to Next Generation Science Standards (NGSS)

Science & Engineering Practices

Analyzing and interpreting data

Disciplinary Core Ideas

MS-PS1.A: Structure and Properties of Matter
MS-PS1.B: Chemical Reactions
HS-PS1.A: Structure and Properties of Matter

Crosscutting Concepts


Performance Expectations

MS-PS1-2. Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.

Answers to Questions

  1. Describe what happened in this demonstration.

Hydrogen peroxide and dishwashing solution were added to a 100-mL graduated cylinder. A small amount of sodium iodide was added, which caused thick foam to erupt from the cylinder.

  1. Write the chemical equation for the decomposition of hydrogen peroxide.

2H2O2(aq) → 2H2O(g) + O2(g)

  1. Why does the dishwashing solution foam?

The water vapor and oxygen gas get trapped in the dishwashing liquid, causing it to foam.

  1. What was the purpose of the sodium iodide? Was it consumed during the reaction?

The sodium iodide served as a catalyst, which is a substance that speeds up a reaction but is not consumed during the reaction. It was not consumed during the reaction.


This demonstration evolves a good deal of heat as shown by the steam coming off of the foam as it is produced. The reaction, therefore, is exothermic. The action of a catalyst is demonstrated. The catalyst is the I(aq) ion which speeds up the decomposition of the hydrogen peroxide. The decomposition of hydrogen peroxide produces steam and oxygen gas. The oxygen gas and water vapor cause the dishwashing liquid to foam.



Special thanks to Jim and Julie Ealy of The Peddie School in Hightstown, NJ.

Stone, C. H. J. Chem. Ed. 1944, 21, 300.

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