How to Do an Osmosis Science Experiment with Baking Soda

Help your children complete a simple science experiment demonstrating osmosis. Watch what happens when water being moved by osmosis has something else dissolved in it. Allow the children to do as many of the steps on their own as they can to facilitate the learning process and build confidence and independence. Afterward, discuss how osmosis works. The water is attracted to the string, which absorbs the water. It brings the baking soda with it and gradually soaks the whole string. But the baking soda, though dissolved, is too large to soak into the string. As the water evaporates, the baking soda crystals can be seen in clumps on the string.

Things You'll Need

• 2 cups
• 12-inch piece cotton string
• 2 tablespoons baking soda
• Food coloring, optional

Instructions

1. Fill the cups about three-quarters full of water.

2. Add 1 tablespoon baking soda to each cup. Add a few drops of food coloring to each cup, if desired.

3. Put one end of the string in one cup and the other end in the second cup. Leave the experiment undisturbed for two days.

4. Examine the string and the cups and make observations. Discuss your findings.

References

• U.S. Forest Service: Dripping Crystals
• I love Bacteria: Egg Osmosis