6: Floating Soap Bubbles

Everyone enjoys blowing bubbles. They are very fragile and difficult to look at close up. However, they are so light that you can float them on carbon dioxide gas to examine them more closely. When you look closely they reveal many interesting properties. When you have seen enough close up, you can try to blow a mega bubble.

What you need

soap bubble solution
a wand for blowing soap bubbles, (you can make one from wire)
Wand for Blowing Bubbles
a large transparent container with an open top (an empty 45dm3 aquarium works well)
shallow glass dish to fit inside the large container (glass baking dish)
sodium hydrogencarbonate powder
vinegar

What you do

  1. Set the large container on a table away from draughts and where you can easily look through its sides.
  2. Place the glass dish inside the bottom of the large transparent container.
  3. Put approx. 20g of sodium hydrogencarbonate in the glass dish.
  4. Pour 250cm3 of vinegar into the dish with the sodium hydrogencarbonate. The mixture will start to fizz immediately as they react and start to produce carbon dioxide. Carbon dioxide is more dense than air and will be held in the large container as long as it is not disturbed by draughts of air.
  5. After the fizzing in the dish has subsided (about a minute), use your wand to blow several soap bubbles gently over the opening of the large container, so that they settle into the container. Be careful that you do not blow directly into the container or you may blow all the carbon dioxide out.
  6. When a soap bubble settles into the container it will not sink to the bottom, as it would in air. Instead it floats on the surface of the carbon dioxide.
  7. Observe the bubble. What colour is it? Does it change size? Does it stay at the same level?

BLOWING MEGA BUBBLES

When you have seen enough you may like to try to blow a mega bubble.
First you need to make your wand (see the diagram).
Wand for blowing mega bubbles
Hold the wand by one of the straws and dip it into the soap solution, withdraw it slowly and wave it gently to and fro to make large bubbles. You can stiffen the straws with wire from a coat hanger if necessary.

OTHER THINGS TO TRY

Try making different shaped wands. Which shape gives the best bubbles?

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