Experiment with Surface Tension

This is my first video production for my blog.  Ta da!  The sound quality will not be great but in 17 seconds it does illustrate an interesting concept in chemistry.  In this bowl is plain tap water.  Floating on top is common black pepper. Add a drop of dish into the bowl.  Watch the pepper dramatically shifts to the sides of the bowl.  What is the science behind this impressive demonstration?  Read on my faithful!

Science Behind Surface Tension

Pepper is hydrophobic. So it repels water.  Its hydrophobic nature also means it does not dissolve in water so it floats on top.  The attraction of water molecules to each other creates surface tension like a skin on the water. Light objects like small insects and pepper can suspend themselves on this “skin” because they are too light to break the surface tension.

Soap is a molecule with two unique ends.  One end is hydrophyllic meaning it is attracted to water. The hydrophobic end is attracted to grease or fatty substances.  The hydrophyllic end and its attraction to water is what causes the unique reaction of pepper quickly moving to the edge of the container.  The soap’s attraction to water on one end causes the surface tension of the water to be disrupted.  Because water wants to maintain surface area, new water, soap-free, moves up to rebuild the surface tension and pushes the soap-water to the edge of the container dramatically pulling the pepper with it.

This is one experiment I encourage you try at home!  No animals were injured or killed during this demonstration.  It is easy and extremely kid friendly.  They will love it – at home or in the classroom!

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