Science

Elephants Toothpaste Demonstration

by Amy Collins October 24, 2019

A popular chemistry demonstration by Senior Science Technician Paul Cook showing the impressive decomposition of hydrogen peroxide.

Learning outcomes

You will be able to:

  • Explain the components, products and process of a decomposition reaction.
  • Describe the function of a catalyst.

You will need (per demonstration):

  • 1 x Shallow Gratnells (F1) tray
  • 1 x 1 litre borosilicate glass volumetric flask
  • 1 x 200ml borosilicate glass beaker
  • 1 x Borosilicate glass stirring rod
  • 1 x Universal tube
  • 1 x Balance
  • 1 x Spatula
  • 14g Potassium iodide
  • 50ml Water
  • 10ml Washing up liquid
  • 100ml 100vol, 30% Hydrogen Peroxide
  • 1 x Protective plastic sheet or a Gratnells Art or A3 Tray to catch any overflow
  • 1 x Safety glasses
  • 1 x Lab Coat
  • 1 x Pair of protective gloves

Preparation:

  • Put on your lab coat, gloves and safety glasses, tie back your hair if it is long.
  • Put the protective sheeting, Gratnells art or A3 tray on a laboratory bench or appropriate table.
  • Put the shallow Gratnells tray on the sheet in the centre of the table or in the middle of the bigger tray.
  • Put the volumetric flask in the centre of the shallow tray.
  • Weigh 14g of potassium iodide into a universal tube using the spatula and balance.
  • Put 50ml water into the glass beaker.
  • Set up your camera or video recording device a safe distance away from the volumetric flask.

What to do:

Take a look at our #WhatsInMyTray – Science Project – Elephants Toothpaste video on YouTube here.

Ensure all spectators and recording equipment are a safe distance away from the demonstration area.

  • Add 14g potassium iodide to 50ml water in a glass beaker and stir to dissolve.
  • Add the potassium iodide solution to the volumetric flask.
  • Add 10ml washing up liquid to the volumetric flask.
  • If you wish to record the reaction, press start on your recording device now.
  • Add 100ml 100vol, 30% Hydrogen Peroxide to the volumetric flask and stand well back.
  • Observe the reaction.

What is happening?

Hydrogen Peroxide (H2O2) is not very stable and naturally decomposes (breaks down) to form oxygen and water. This decomposition is slow and is not usually noticeable. Potassium iodide catalyses (speeds up) the decomposition of hydrogen peroxide, forming water and oxygen more quickly.

The decomposition reaction can be shown as:

2H2O2 → 2H2O + O2

This is an exothermic reaction (produces heat), you may see some steam produced in the video where the water produced in the reaction is vaporised.

The oxygen released during the reaction is trapped into bubbles by the washing up liquid, which are forced out of the top of the volumetric flask in a spout of foam. The shape of the volumetric flask accelerates the foam spout, the pressure is higher in the smaller volume of the slim flask neck.

The reaction is referred to as elephant’s toothpaste because of the large quantity of foam produced, imagine how much foam would be produced by a huge elephant brushing its teeth!

Other things to try…

  • If you would like to carry out a decomposition reaction but need to avoid using potassium iodide and would also like to use a lower concentration of hydrogen peroxide, try our colourful Funky Foam What’s In My Tray activity, which uses commonly available reagents and can be carried out by the students themselves.
  • How could you show that the gas produced by the reaction and trapped by the bubbles is oxygen?
  • Why does the reaction stop?
  • Can you experiment with the volume, quantity or concentration of the reagents to prolong the reaction? Discuss your ideas with your teacher or technician to set up a second demonstration. Be sure to work carefully and within CLEAPSS guidelines.
  • Can you model this decomposition reaction using molymod®
  • Share your photographs/videos on social media using #WhatsInMyTray

Health & Safety

As with all Gratnells Learning Rooms What’s In My Tray Activities, you should carry out your own risk assessment prior to undertaking any of the activities or demonstrations. In particular, CLEAPSS guide SRA011 Elephant’s Toothpaste and HazCard HC050 Hydrogen peroxide should be consulted.