|MadSci Network: Chemistry|
I didn’t know too much about bubbles or bubble formation, so I did a little research. I am now a semi-expert in the field of bubbles! First, to understand what’s going on let’s say you wanted to make bubbles with pure water. From experience, I know you can make bubbles using pure water, but they don’t last too long. To see this we need a glass of water and a straw. Put the straw in the glass and start blowing. Stop blowing and look at the top of the water. You should see some water bubbles at the top, but they will quickly pop.
But why do these bubbles pop so quickly? Well, they are made of an extremely thin layer of water. We know that water evaporates, so we can say that the water evaporates from the surface of the bubble until a weak spot forms on the bubble and it pops. Remember that the water bubble is extremely thin, so even though water may not evaporate that quickly, it still evaporates fast enough to make the bubble pop quickly. Also, gravity tries to pull the water at the top of the bubble down. This forms a weak spot at the top of the bubble causing it to pop.
Now we might wonder what holds the water bubble together in the first place. We know that one water molecule is made up of two atoms of hydrogen and one atom of oxygen – and so we get the formula H20. Water, like a lot of other molecules, is able to do something chemists call “hydrogen bonding.” The electrons in a water molecule stay closer to oxygen most of the time, and this gives the oxygen a slightly negative charge (remember that electrons have a negative charge). As a result, the hydrogen atoms will have a slightly positive charge. When we have a lot of water molecules together, like in a glass full of water, something amazing happens. The negative part of one water molecule (the oxygen atom), will attract the positive part (the hydrogen atom) of another molecule. This is hydrogen bonding. It’s not an actual bond, but more like a strong attraction between water molecules.
Because water molecules want to stick together, they have the ability to form bubbles. This attraction isn’t too strong, though, otherwise a pure water bubble would stay together forever (assuming the water didn’t evaporate).
Now let’s try to figure out how to make a “super bubble” – one that will last longer than a water bubble. We can attack this problem from two directions. We can either try to find a way to keep the water in a bubble from evaporating, or we can try to find a way to strengthen the “hydrogen bonding” effect within water.
I’m not to sure how to increase the hydrogen bonding effect, but I do know how to keep water in a bubble for evaporating – by using soap! A soap bubble really has three layers! The inside and outside layers are made of soap and the middle layer is made of water. The outer layer keeps the water from evaporating quickly.
Now we have to answer why the bubble has three layers. It has to do with the soap itself. Soap is made up of really long molecules. One small part has a charge, and the rest has no charge! The part with the charge is attracted to water, and the part with no charge is repelled by water. The long part with no charge is like grease, and we know that grease doesn’t evaporate (or at least doesn’t evaporate quickly), so it protects the inner layer of water.
To make bubbles that last longer, you can looks for greasy type materials around the house that will dissolve in water. Trying cooking oil, however, will not work because the molecules that make up cooking oil have no charge anywhere – they are completely neutral and will never dissolve in water. For a molecule to be able to dissolve in water, it must have a charge somewhere.
A lot of things tend to affect bubbles. Sunlight helps water evaporate faster, so it will lead to bubbles with short lives. If you touch a bar of soap to a bubble it will most likely pop because it breaks down the three layer structure of a bubble. The soap in the bar interacts with the soap in the bubble, which destroys the delicate balance between soap and water in the bubble.
I’m not really sure how vinegar or salt would affect bubbles. The only way to find out is to conduct an experiment! There are some good mixtures that will make long lasting bubbles. One I found consists of the following:
These web sites should be able to provide you with some interesting bubble solutions to try (one involves corn syrup!):
If you want to look at the structure of a bubble, these web sites have some good graphics and general information:
Also, if you would like to find more information on hydrogen bonding, any good chemistry book should be able to provide information and graphics.
Try the links in the MadSci Library for more information on Chemistry.