Polar vs. Nonpolar Liquids

Lesson Plan - Get It!

Audio:

Let's begin today's lesson with an experiment to determine some of the primary differences between water and cooking oil!

For this experiment, you will need:

• a faucet with running water
• a balloon
• cooking oil (vegetable, olive, etc.)
• a disposable cup with a small hole cut into the bottom

You are about to discover what effects a charged balloon has on a stream of water and a stream of oil. What do you think will happen when you hold a charged balloon close to a stream of water? What do you think will happen when you hold a charged balloon close to a stream of oil? Do you think there will be any difference at all? Discuss your hypotheses with a teacher or parent before you continue.

Now, it's time to perform the experiment:

1. Blow up the balloon and tie it.
2. Quickly rub the balloon against your hair or a piece of wool for about one minute.
3. Turn on a faucet so you have a thin, slow, steady stream of water. If the water is running too hard and quickly, the experiment will NOT work. Hold the balloon about one inch away from the water. Observe and record what you see.
4. Next, cut a small hole into the bottom of a disposable cup. You can accomplish this by poking a pencil or straw through the bottom of the cup.
5. Re-charge the balloon by quickly rubbing it against your hair or a piece of wool for one minute.
6. Have a teacher or parent pour oil into the cup so a small stream of oil runs out the bottom. It would be best to perform this part of the experiment over a garbage can or outside.
7. While someone is pouring the oil, hold the balloon about one inch from the stream of oil. Record your observations.
8. Compare and contrast your results.
9. Discuss the outcomes with a teacher or parent.

When you held the balloon next to the water, you should have noticed that the stream of water moved. You also should have observed that the oil went completely unaffected by the charged balloon, and continued in a straight stream. Why do these liquids have different reactions to the charged balloon?

Liquids can be grouped into two categories: polar liquids and nonpolar liquids.

A liquid's grouping is determined by its atomic structure. If you are uncertain what is meant by atomic structure, review the Elephango lesson under Additional Resources in the right-hand sidebar. Remember, everything is made of atoms, and every liquid is formed when certain types of atoms bond together to make a molecule.

Water is a polar liquid because the distribution of its electrons in the molecule causes it to have a positive charge on one end and a negative charge on the other end.

Oil is a nonpolar liquid because its electrons are evenly distributed along the molecule, causing it to have neither a positive nor a negative charge. Therefore, polar liquids have a positive and a negative charge, while nonpolar liquids have no charge.

How does this affect the balloon experiment? When you rubbed the balloon against your head or wool, it became negatively charged. When it comes to molecules, opposites attract. The negatively-charged balloon reacted to the positive charge in the water molecules, causing the water to move. Since oil is a nonpolar liquid, it did not react to the charge of the balloon.

To continue learning about polar and nonpolar molecules, watch Crash Course's Polar & Nonpolar Molecules: Crash Course Chemistry #23:

Look at the images from the beginning of the lesson. What is the difference between water and oil? Explain your answer to a teacher or parent.