You and Your Students!
Vicki Cobb, Education World Science Editor
Do a simple test to compare cleaning solutions. Which surface cleaner is really best?
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!
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.
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
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