Starring

You and Your Students!

Script By

Vicki Cobb, Education World Science Editor

Synopsis

Do a simple test to compare cleaning solutions. Which surface cleaner is really best?

Genre

• Chemistry
• Physical science

Required Props

• small slim olive jars, as many as you can collect
• measuring cup
• measuring spoons
• salad oil
• assortment of soaps: liquid, soap flakes, detergents
• assortment of hard-surface cleaners, Fantastik, Mr. Clean, Windex, etc.
• clock
• pencil and paper

Setting the Scene (Background)

My house is being painted, so I've been doing a lot of cleaning lately. Amazing how a layer of dirt builds up on untouched picture frames and knickknacks. Water, the cheapest and most abundant cleaner around, is not the most efficient. Although it is called the "universal solvent" because more chemicals dissolve in water than in any other liquid, there is a large class of compounds that simply don't mix at all with water -- including the greases and oils that magically settle on household surfaces.

In addition to elbow grease, soaps and detergents are called to the rescue. They are substances that mix with both greases and water. When oil, water, and soap are mixed together the oil is held in a suspension called an emulsion. Although the emulsion is often temporary, it lasts long enough to flush away the grease along with the dirt.

Supermarkets offer an array of products that form emulsions. But which is the best one?

Despite claims on TV that almost every cleaner is the best cleaner, you and your students can do some simple product testing to find the most efficient cleaner by using this lesson in chemistry, the scientific process, and consumer skepticism. It's also a lot of fun!

Stage Direction

The manner in which you perform this experiment will depend on how many clean olive jars you can collect. If you collect only four or five jars, do the experiment as a demonstration for the class. If you get enough jars for a group of four or five kids to work cooperatively, they can make the discoveries themselves and share them with other groups.

Show-Biz Science is scripted by popular children's book writer Vicki Cobb. Click to learn more about Vicki or to read a brief synopsis of her philosophy of teaching science. Visit our archive of archive of Show-Biz Science Activities. Watch for a new activity each week. Then chat with Vicki -- share your feedback and ask your questions about teaching science -- on our special Showbiz-Science message board. Be sure to visit Vicki's Kids' Science Page for more great science fun, a complete list of her books, and information about how you can invite Vicki to come to your school. And don't miss her library of science videos too. Or visit Vicki and other great authors of nonfiction for children at the INK Think Tank.

Plot

Act I

• Put a quarter cup of cold water and one tablespoon of salad oil in each jar.
• Put the lid on one jar containing oil and water and label this "control." (A control has all of the elements of an experiment except the one you are changing.)
• Collect a variety of cleaners and add one teaspoon of each soap or hard-surface cleaner to one of the other jars. Label each jar so you know which cleaner was used.
• Shake the jar containing oil and water hard about five times. Use the second hand on a clock to determine how long it takes for the shaken liquid to separate into two clear separate layers -- oil and water. I found that my sample separated in about forty-five seconds.
• Now shake a jar containing one of your cleaning solutions five times. Measure the time it takes to separate into two separate layers.
• Repeat for each setup of oil, water and cleaner.

Behind the Scenes

The longer it takes for the oil and water to separate into two layers, the better the emulsifier. The better the emulsion, the more time you have to rinse away dirt. I found that liquid soap was better than hard-surface cleaners. And some brands of liquid soap were faster than others. Try powdered cleaners too. Dissolve a small amount in water before you add a teaspoon to the oil-water mixture.

Do another experiment to see how water temperature affects the time before an emulsion separates.

Article By Vicki Cobb
Education World®
Copyright © 2006 Education World

01/19/2006