Fun science: Elephant’s Toothpaste

It might be called Elephant’s Tootpaste, but I really don’t hope elephants actaully use it.

The recipe is simple enough:

You take:

  • 50-100 ml of 30% hydrogen peroxide (H2O2) solution
  • liquid dishwashing detergent
  • saturated potassium iodide (KI) solution

Then follow these steps:

  1. Pour ~50 mL of 30% hydrogen peroxide solution into the graduated cylinder.
  2. Squirt in a little dishwashing detergent and swirl it around.
  3. You can place 5-10 drops of food coloring along the wall of the cylinder to make the foam resemble striped toothpaste.
  4. Add ~10 mL of potassium iodide solution. Do not lean over the cylinder when you do this, as the reaction is very vigorous and you may get splashed or possibly burned by steam.
  5. You may touch a glowing splint to the foam to to relight it, indicating the presence of oxygen.

The chemistry of the reaction is:

he overall equation for this reaction is:

2 H2O2(aq) → 2 H2O(l) + O2(g)

However, the decomposition of the hydrogen peroxide into water and oxygen is catalzyed by the iodide ion.

H2O2(aq) + I(aq) → OI(aq) + H2O(l)

H2O2(aq) + OI(aq) → I(aq) + H2O(l) + O2(g)

The dishwashing detergent captures the oxygen as bubbles. Food coloring can color the foam. The heat from this exothermic reaction is such that the foam may steam. If the demonstration is performed using a plastic bottle, you can expect slight distortion of the bottle from the heat.

Right, enough talk. It looks like this:


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