K-6, Middle school, High School
In this experiment, you'll combine intermolecular forces and the law of reflection to make an incredible looking glass egg.
Molecules can be divided into two categories, polar and non-polar. When elements combine to form bonds, they don't always share the electrons in their bonds equally, causing one element in the bond to develop a slightly negative charge and the other to develop a slightly positive charge. When this happens, the bond is said to be polar.
Depending on the shape of the molecule, polar bonds can add to each other, making the entire molecule polar (one side slightly positive, the other slightly negative).
Because opposite charges attract, polar molecules are naturally attracted to each other in the same way magnets with their north and south poles are attracted to each other.
Water is polar. It has polar bonds between hydrogen and oxygen that combine to make the molecule polar. As a result, other substances that are polar will tend to be attracted to water. Such substances are said to be hydrophilic, meaning "water loving".
On the contrary, substances that are non-polar are not attracted to water. These substances are said to be hydrophobic, meaning (you guessed it!) "water fearing".
In this experiment, you will coat the outside of an egg with soot from a candle flame. That soot is non-polar, and therefore hydrophobic. In other words, it will repel water. As a result, when you submerge the soot covered egg under water, a thin layer of air will exist between the egg and the water.
How does this make the egg look like glass? Have you ever seen your reflection in the surface of water? How about in a glass window? Whenever two substances meet that allow light to speed up or slow down (a phenomenon called refraction), reflection occurs at the interface. Your egg will appear glassy because instead of seeing light from the soot covered egg, you'll be seeing the light that reflects from the water-air interface.
SUPPLIES, TOOLS, MATERIALS
- A clear container or cup large enough to fit an egg
*Suggest hard boiled for younger scientists
You'll be working with an open flames. Fire is hot. Be careful!
- Light your candle and make sure the surface of the egg is very dry.
- Hold the egg near the tip of the flame, adjusting the height until you notice black soot begin to deposit onto the egg shell.
- Rotate the egg until the entire surface is very dark black. Your fingers will get a little messy. DO NOT WEAR GLOVES! The only thing worse than burned fingers is molten flaming latex that you can't get off your fingers.
- Submerge the egg under water and record your observations!
QUESTIONS TO CONSIDER
- Look up and define the following terms:
Law of Reflection
- Can you think of another substance you could have used to coat the egg that would have produced similar results? Try it!