Cloud Bottle

Concepts – air pressure, evaporation, ideal gas law

Materials – 1-liter bottles, rubbing alcohol, dropper, #3 rubber stopper, sports ball air pump with a metal needle, vegetable oil

Getting Ready – put a little bit of oil on the tip of the air pump needled; this will act as a lubricant. Using a firm, consistent pressure push the metal needle of the air pump through the center of the rubber stopper. Ensure the whole of the needle where the air comes out is all the way through the stopper.

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Figure 32: Some items you will need to make the cloud in a bottle.

Procedure – put five drops of rubbing alcohol in the bottom of the 1-liter bottle. Swirl the bottle around to spread the alcohol around the bottom. Put the rubber stopper in the bottle ensuring there is a good seal. While holding the stopper down against the bottle, pump the air pump 10-12 times. Quickly pull the stopper out of the bottle and a cloud should appear. Have students make an inference explaining why the cloud formed. After a few minutes the cloud will disappear. Simply pumping the bottle up again and pulling the stopper out quickly will cause the cloud to reappear.

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Figure 33: Ensure the stopper and one-liter bottle have a good seal.

Explanation – When the rubbing alcohol is added to the bottle and swirled around some of it evaporates into the air. Pumping air into the bottle compresses the alcohol molecules together. Pulling the stopper out quickly releases the pressure, allows the air to expand, and subsequently causes the temperature of the air to becomes cooler. The rapid cooling process causes the alcohol molecules to condense, forming a cloud. In this case the cloud is liquid alcohol suspended in a gas mixture (air). The liquid alcohol particles suspended in the air scatter light in all directions causing the white color.


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Figure 34: a cloud is created.

*This activity was adapted from “Cloud in a Bottle” on SteveSpanglerScience.com.

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