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I hope you can help me. I am Irish, but I go to school in North London as my parents live here. I am working on an experiment on how to take soap out of water. I have blown air into the soapy water for hours but more and more bubbles seem to appear. I have 2 questions:

1. If I blow air into the water for long enough will doing this take the soap out of the water?

2. If I vacuum the soap bubbles will it burst them?

Question Date: 2012-12-18
Answer 1:

I don't think that blowing air into water will really take soap out of water. When we put soap in water, it dissolves because of the hydrophilic or "water loving" end of soap molecules. So if you want to remove the soap from the water, the best way might be to react it with something, such as calcium carbonate. When soap reacts with calcium carbonate it generates calcium stearate, which is insoluble in water and you can filter off.

Regarding your second question, if you vacuum the soap bubbles with something like a vacuum cleaner, they will indeed "burst" because the pressures inside and outside the bubbles will become dramatically different over a relatively short period of time. I hope this helps!

Answer 2:

Soap dissolves in water. There is no way physically to get it out - you have to use the differences in the chemical properties of the two.

The only suggestion that I can give you is to distil the water. I don't know what the evaporation temperature of soap is, but if it's higher than that of water, then you could boil the water and let the vapor condense on another surface. This condensed water would be soap- free.

Answer 3:

Thanks for the great question! Soap makes water form into bubbles because the soap forms a very thin film that prefers to "coat" the surface of the water that is exposed to air. The reason for this is that, soap makes the interface (the surface where water touches air) between air and water more stable (longer lasting, more likely to form). This explains why so many bubbles form after stirring or agitating the water: all of the bubbles you form while stirring or blowing last much longer in soapy water than in pure water. Also, you will notice that the bubbles create much more area where the water is touching air.

As a result, almost all of the soap will come to the surface of the water if you let the water sit still (no stirring, blowing into, or otherwise agitating the water) for a long time. Once the soap is at the surface, a vacuum can be used to suck the soap off of the surface of the water. Be careful to just get the surface layer, since this is where the soap is! An interesting side note is that we use this sort of technique in the research lab for some experiments of our own!

I don't think that blowing into the water will remove all of the soap without the vacuum. However, try blowing into the water after using the "vacuuming-the-surface" technique described above. If you successfully removed most of the soap, then the water should form less bubbles.

Good luck with your interesting experiment! Feel free to let us know if you are successful!

Answer 4:

1. It is unlikely that blowing air will remove any significant amount of soap. When the bubbles pop, most of the soap returns to the water below. Also, even if the solution stops forming bubbles, the soap is probably still there, but is just interacting with dirt or other particles (so it is unable to form bubbles).

2. Likely, but it will be a fun experiment to test yourself!

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