June 2017:

Have you ever laid out in the summertime looking up in the sky at the clouds and imagined what animal shape the cloud has made? What is a cloud and can I make one?

Materials:

• 2 L empty transparent plastic bottle with a lid
• matches
• warm water

Warning! When using matches make sure there is an adult to help.

Experiment:

Add a small amount (teaspoon or so) of the warm water to the bottle. Squeeze the bottle a bit with the lid off and have an adult light a match and gently blow out the match as it sits in front of the opening of the bottle.   Release the pressure on the bottle to try and draw some of the smoke into the bottle. If no smoke goes in, you can drop a freshly blown out match into the bottle and tightly cap the bottle. Squeeze the bottle multiple times.

What’s happening?

You’ll notice that as you squeeze the bottle that the bottle is completely transparent but that when you release the pressure a cloud is formed. Clouds are tiny droplets of water molecules in the air. They are formed when moist warm air rises into the atmosphere and as the air rises it cools, causing the water vapor to form those tiny water droplets. When you squeeze the bottle you cause the air in the bottle to warm slightly and when you release the pressure in the bottle, the air cools. So why are the matches needed? The clouds also need a small surface of something for the water molecules to form onto. This might be salt particles from the ocean spray or other pollutants in the air. The smoke from the match gives those tiny water particles a surface to condense onto inside the bottle.

Greater pressures can be created by using a pump but that will take more work!

Reference:

http://www.physics.org/interact/physics-to-go/cloud-in-a-bottle/

Paul Brandt

To view all past “ChemShorts for Kids”, go to: http://chicagoacs.org/articles/article_category/1