Science

Funky Foam!

by dontregartha September 28, 2017

A colourful decomposition reaction using common household ingredients.

 

Learning outcomes

You will be able to:

  • Describe the method, reagents and products of a simple decomposition reaction.
  • Identify and describe the role of a catalyst.

You will need (per demonstration):

  • 1 x Test tube rack (powder-coated metal) sufficient for 5 x 60ml test tubes and 5 x 25ml test tubes
  • 5 x 60ml glass test tubes (large)
  • 5 x 20-25ml glass test tubes (small)
  • 1 x 100ml plastic or glass beaker
  • 1 x 25ml glass measuring cylinder
  • 2 x Glass stirring rod
  • 5 x 3ml plastic pipettors
  • 2 x Shallow Gratnells (F1) trays
  • 1 x Gratnells mini tray or a 50ml plastic or glass beaker
  • 15ml washing up liquid
  • 1 x 7g packet fast acting bread yeast
  • 60ml warm tap water
  • 125ml 6% Hydrogen Peroxide
  • 1 x 28ml bottle yellow food colouring
  • 1 x 28ml bottle red food colouring
  • 1 x 28ml bottle blue food colouring
    Safety goggles
  • Lab coat
  • Gloves
  • Camera and video recording equipment (optional)

Preparation:

Take a look at our Funky Foam video.

  • Work in a shallow Gratnells (F1) tray to contain any drips and the products of the Funky Foam reaction.
  • Place the test tube rack into the centre of the shallow tray.
  • In the five small test tubes, make up the desired colours using three plastic pipettors to measure out the required quantities of each of the primary colours. For example, in the video we used (left to right):
    • Small test tube 1 = 7ml blue food colouring
    • Small test tube 2 = 3.5ml blue food colouring and 3.5ml red food colouring
    • Small test tube 3 = 7ml red food colouring
    • Small test tube 4 = 3.5ml yellow food colouring and 3.5ml blue food colouring
    • Small test tube 5 = 7ml yellow food colouring
  • Place the small test tubes into the test tube rack.
  • In the 100ml beaker, make up a yeast solution by adding 7g dried yeast into 60ml warm tap water. Give it a good stir and leave aside until needed. Tip: Only make the yeast solution when you are ready to complete the rest of the experiment as it needs to be fresh.
  • Using the measuring cylinder, add 25ml 6% hydrogen peroxide to each of the five large test tubes and stand them in the same test tube rack. You will be adding the other reagents to this large test tube during the demonstration.
  • Pour sufficient (20ml) washing up liquid into a Gratnells mini-tray or 50ml beaker and leave aside until needed.

What to do:

You are now ready to start your demonstration. The following steps are all shown in the video.

  • Using a plastic pipettor, add 3ml washing up liquid to each large test tube (already containing the 25ml hydrogen peroxide).
  • Pour one small test tube of food colouring mixture (7ml) into each large test tube.
  • Swirl to mix the reagents, or stir each test tube with a glass stirring rod in turn (Tip: Work from lightest colour, yellow, through to darkest colour, blue, with your stirring rod to enable you to use the same rod).
  • Give the yeast solution a final stir. You are now ready to add the yeast solution, which will start the reaction. You may wish to set up and start your video recording device now.
  • Using a clean plastic pipettor, add 3ml yeast solution to each of the large test tubes and observe the reaction. Foam in five different colours should travel up the sides of the test tube, over the top and down the sides into the tray.
  • Once the reaction has finished the 6% Hydrogen Peroxide will have fully decomposed. The contents of the test tubes can be disposed of in the sink using plenty of water.

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. Yeast 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). The oxygen released during the reaction is trapped into bubbles by the washing up liquid, which are forced out of the top of the test tube in a cascade of coloured funky foam.

Other things to try…

  • What happens if you use cold water to make up the yeast solution instead of warm? How will you measure this? Why does this happen?
  • What happens if you add a larger volume of yeast solution?
  • Does the colour of food colouring used affect the reaction?
  • How could you show that the gas trapped by the bubbles is oxygen?
  • Why does the reaction stop?
  • Can you model this decomposition reaction using molymod®?
  • How could this reaction be made faster and more spectacular? Tip: Look up spectacular elephant’s toothpaste demonstrations on YouTube.
  • Share the photographs and videos of your demonstration 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, Hydrogen Peroxide is corrosive and deteriorates over time, it should be kept in its original container the fridge until use and used within 6-12 months of opening (see manufacturer’s advice). See the CLEAPSS HazCard for Hydrogen Peroxide. The demonstrator should wear gloves, safety goggles and a lab coat.