6, Decomposition reactions

Dragons toothpaste

Important: Please wear safety glasses and use latex or plastic gloves for this experiment. H2O2 (peroxide) is bad for your eyes and can bleach your skin. If you do get it on you, don't panic. Calmly wash it off with cold water.

dragon-teeth-brush

Mathylda got cavities, which is odd isn't it? We don't think of animals (even dragons) getting tooth decay, and it's true, in general they don't suffer with it. Why?

Animals chew on more hard materials e.g. bone or tree bark, which help to keep their teeth clean. However, domesticated animals can develop cavities if they eat a lot of sugar, so be nice to your pets and keep them away from the sweet stuff.

Mathylda, like way too many humans, eats too much sugar which as they say, rots your teeth. Humans have learnt that brushing their teeth helps prevent decay. For Mathylda we need something a bit stronger, and dragons toothpaste is just the thing.

Dragon Toothpaste

Dragon Toothpaste (often called Elephant toothpaste) is a catalytic chemical reaction using peroxide and yeast (yeast is the catalyst). The reaction creates a blob of soapy foam (the amount of foam depends on the strength of peroxide you use). You can buy 6 - 12% peroxide solution from Amazon (see our ingredients list) which will give reasonable results. You can also buy 30% hydrogen peroxide (taking great care since hydrogen peroxide is VERY corrosive), at any swimming pool supply store and most beauty salons.

In the video below we're using 12% and as you can see the results are fine and certainly not dangerous.

We use peroxide (H2O2), in water (H2O). then add a catalyst to the peroxide (the yeast). This creates a chemical reaction as follows: H2O2 > H2O + O2, or in english, peroxide is catalysed to give water and oxygen.

If you mix in a little detergent you can capture that released oxygen in the form of bubbles. Add food colour and you get coloured bubbles.

Remember that one drop of liquid contains trillions of molecules, so as the hydrogen peroxide breaks down, you get a lot of oxygen really quickly, so you get A LOT of bubbles.

Here’s what you need:

  1. A conical flask (use an empty plastic drink bottle if you’re not using the Kate Witch apparatus set
  2. 1/4 cup or 60ml of 3-30% hydrogen peroxide (a strong peroxide gives more exciting results)
  3. Dish detergent (1 tablespoons)
  4. Food colouring (a few drops)
  5. 1/2 teaspoon (or half a packet) of yeast dissolved in warm water. It must be warm, not cold and not boiling (which kills the yeast).

Fill your flask or bottle with a 1/4 cup or 60ml of peroxide. If you're using 30% peroxide, start with half that.

Add the dish detergent and gently swirl. It's useful to add a few drops of food colour, if you're careful you can try adding two colours on different sides on the flask.

Next we need to prepare the catalyst (yeast). Add the yeast to a 40ml of warm water and wait a few minutes. The yeast will act as a catalyst, releasing oxygen from the hydrogen peroxide.

When you add yeast to peroxide the reaction will create lots of bubbles made from detergent, water, and oxygen. You might observe that the foam is warm because this reaction is exothermic, meaning, as we now know, that it gives off heat.

Let’s experiment

Try adding dry yeast to one flask, and a yeast / water mix to another.

Play around with the amount of peroxide, detergent, yeast and type of container to create the best geyser of foam.

The reaction will release O2 (Oxygen) gas which will create a large amount of foam, perfect as a toothpaste for dragons.

If you like, you can add a different catalyst to the hydrogen peroxide. A good one is magnesium dioxide. Be careful this one can get hot!

Place some magnesium dioxide into a potion jar then pour in some hydrogen peroxide. You can buy the magnesium dioxide from amazon, or if you prefer, pull apart a cheap d-cell battery (cheap batteries are the best source of magnesium dioxide). If you try the D-Cell option beware, it's all a bit messy and takes some time.

You need to make sure you use a copper-zinc d-cell. These have a copper rod in the centre, a zinc can on the outside and in between is a black paste of magnesium dioxide. Here's a great video on it:

To see what happens when you mix hydrogen peroxide with magnesium dioxide, check out this video below (no I’m not sure about the music either….)

The reaction is slightly exothermic as well, and you should use a good Pyrex beaker.

Always wear safety goggles!

Extra points

  1. This involves lighting matches, so please ask your parents first. Let’s see if it’s true what they say about oxygen. Does it burn? You bet it does. Add a little (say 10ml) H2O2 and yeast in a flask and let the oxygen build up. Then light a match, blow it out and dip it into the gas in the tube. What happens and why?
  2. Hydrogen peroxide is highly reactive and has a lot of uses. See if you can find three separate uses for this amazing chemical around the home and in industry.