Materials
Rubbing (isopropyl) alcohol
Vegetable Oil
A plastic container or glass jar with an interesting shape (long, skinny olive jars and the fancy jars that hold some marmalades, jams or jellies work well)
Small beads, sequins, glitter, or other tiny, shiny things
Food coloring (optional)
Clear tape (optional)
Content Provider
© The Exploratorium
www.exploratorium.edu
Explanation
Why doesn't the oil float on top of the alcohol?
Since oil floats on top of water, you might have thought that oil would float on top of alcohol, too. But the oil sinks to the bottom and the alcohol floats on top of the oil. Even though water and alcohol are both clear liquids, they have different densities. Alcohol floats on top of oil because a drop of alcohol is lighter than a drop of oil the same size.
Why don't oil and alcohol mix? For that matter, why don't oil and water mix?
The answers to these questions have to do with the molecules that make up oil, water, and alcohol. Molecules are made up of atoms, and atoms are made up of positively charged protons, negatively charged electrons, and uncharged neutrons.
The atoms that make up water molecules and alcohol molecules are arranged so that there is more positive charge in one part of the molecule and more negative charge in another part of the molecule. Molecules like this are called polar molecules.
The charged particles in an oil molecule are distributed more or less evenly throughout the molecule. Molecules like this are called nonpolar molecules.
Polar molecules like to stick together. That's because positive charges attract negative charges. So the positive part of a polar molecule attracts the negative part of another polar molecule, and the two molecules tend to stay together. When you try to mix water and oil or alcohol and oil, the polar molecules stick together, keeping the oil molecules from getting between them-and the two don't mix. When you try to mix water and alcohol, they mix fine, since both are made of polar molecules.
What's this pretty toy doing in a set of science experiments? It seems more like an art project to me.
When you make a Glitter Globe, you're experimenting with two liquids that won't mix with each other--alcohol and oil. Playing with the Glitter Globe gives you a chance to watch how liquids flow. And in the process, you make something that's pretty.
Some people think that science and art have very little in common. At the Exploratorium, we disagree. Both artists and scientists start their work by noticing something interesting or unusual in the world around them. Both artists and scientists experiment with the things they have noticed. Art and science begin in the same place-with noticing and experimenting.
Procedure
- Fill about ¼ of the jar with rubbing alcohol. Add a drop of food coloring.
- Pour vegetable oil into the jar, leave about ½ inch or air at the top of the jar. Let the globs of oil settle.
- Is the oil on top of the alcohol or underneath it?
- Drop glitter into the jar. Use as much as you want. Don’t use anything heavy that might break the jar.
- When all the glitter is in the jar, carefully pour in more oil until the jar is completely full-right up to the rim.
- Screw the lid of the jar very tightly. You can use tape to put around the lid to make sure that it does not leak.
- Gently shake the jar. The oil and alcohol will mix and turn a milky color, and the glitter will float and spin.
- Let the oil settle again. That will take about 5 to 10 minutes. Now spin the jar instead of shaking it.
Description
This laboratory activity can be used in the Physical Science or Chemistry classroom while discussing positive and negative charges (polarity). This activity will demonstrate to students that oil and alcohol have different densities, that there are more polar molecules in the alcohol, and that there are more nonpolar molecules in the oil. The students can display these concepts making a toy that sparkles!
Website(s)
The Science Explorer - Glitter Globe
Assessment
Have students answer the questions that go along with the lab as they are working on it. After they complete the lab, have them answer the questions below.
- Why doesn't the oil float on top of the alcohol?
- Why don't oil and alcohol mix? For that matter, why don't oil and water mix?
- Explain the difference between polar and nonpolar molecules.
