Homeschool Curriculum – Suds and Soft Water

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Nearly everyone uses tap water, as it is readily available in many parts of the country.

Getting Started

Nearly everyone uses tap water, as it is readily available in many parts of the country. In this project, which is great for nearly any chemistry homeschool curriculum, you’ll learn about how tap water contains some minerals that interfere with some detergents. Your chemistry homeschool curriculum will be easier to understand when you apply water softeners to tap water to understand exactly how they work.

Water softeners are intended to remove the minerals from tap water that cause tap water to “harden.” You’ll then be able to determine whether hard water or soft water gets better doap suds.

Once you’re ready to get started, you’ll need to gather just a few materials together:
    •    2 cups of distilled water
    •    1 teaspoon of Epsom salt
    •    2 empty 2-liter plastic soda containers (they should be cleaned and still have the screw-on caps)
    •    A few drops of liquid dishwashing detergent (but not the kind used with automatic dishwashers)

You may have noticed that the bottle without the Epsom salt got more suds than the bottle with the salt in it.

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Procedure

After you’ve gathered these materials together, you should be ready to get started. If so, then follow these simple steps:
   •   Pour one cup of the distilled water into the empty soda bottles (each).
   •   Add 1 teaspoon of the Epsom salt to only one of the bottles.
   •   Swirl the bottle around so that the salt dissolves into the water.
   •   Add a few drops of the dish washing liquid to both of the bottles.
   •   Put the caps back on the bottles.
   •   Shake both bottles.
   •   You will notice that one of the bottles has more suds than the other.
   •   Record your observations.

The water with the salt combines with soap to form a scum that does not dissolve in water (often causing soap scum in bathrooms).

Understanding It All

Understanding what you observed:
You may have noticed that the bottle without the Epsom salt got more suds than the bottle with the salt in it. Here’s why: suds are actually tiny bubbles that are formed when air is trapped in a liquid film. This air becomes trapped in the film when the film is shaken in the water. Therefore, the film is made of liquid detergent and water. The molecules that are in the detergent hold the water molecules in place within the film of the bubble.

By the way, if you teach science at home and are looking for more hands-on experiments for your science curriculum, a great resource is the free Homeschool Science Experiment Guide and workbook.

Conclusion

When you have hard water, the water is usually made of minerals that contain elements of calcium and magnesium. Adding the Epson salt to the water made it hard. Epsom salt is magnesium sulfate. You also observed that calcium and magnesium deposits in water interfere with the cleaning action of soap because the water with the salt in it does not form bubbles as well as the water without the salt. Instead, the water with the salt combines with soap to form a scum that does not dissolve in water (often causing soap scum in bathrooms).

There are a few ways to soften water. Many water supply pipes have an automatic water softener attached to them that automatically removes magnesium and calcium and replaces those elements with sodium, which does not react with soap. I bet you didn’t think you’d learn about how to maintain a clean bathroom with this experiment!