Students can experiment with substances to discover the different ways water molecules can interact, including in hydrophilic and hydrophobic ways. Hydrophilic means water loving and refers to substances that bond transiently with water. Hydrophobic, by contrast, means water fearing and refers to substances that repel water. Capture student interest with participatory activities that bring these concepts to life as children explore the fundamental properties of water molecules through observing interactions with hydrophilic and hydrophobic substances.
Contact Angle Investigation
Investigate the practical implications of hydrophilic and hydrophobic substances by observing the impact of windshield treatments on water droplets. Explore how the contact angle -- the shape a water droplet forms on a surface -- influences whether water forms into droplets or sheets. Provide students with three glass slides. Leaving one slide untreated, have students coat one slide with rain-repellant treatment and one slide with anti-fog treatment. Have students use eyedroppers to drop water onto each slide, observing and comparing the results. Instruct students to tilt each slide to observe the motion of the water to finally decide if each surface is hydrophilic or hydrophobic. Ultimately, students should express how the windshield treatments improve driver visibility.
Let students discover what happens when a substance that is both hydrophobic and hydrophilic is added to milk. Pour 2 percent milk onto a plate until it is 1/4 inch deep. In the center of the milk, have students add a few drops of food coloring. The food coloring allows students to see the interaction of the hydrophilic and hydrophobic molecules when you next add soap. Have students touch a cotton swab to the center of the milk and observe that nothing happens. Instruct students to put a drop of dish soap on the other end of the cotton swab and hold it in their plate of milk. Observe what happens and discuss with students the effect of the soap on the milk.
Making Magic Sand
Allow students to compare how hydrophilic sand and hydrophobic sand interact with water. Make "magic sand" by spraying sand with several coats of silicon spray. Allow the treated sand to dry overnight. Have students fill plastic cups halfway with water. Give them some of the silicon-coated sand to put in their cups, and have them observe what happens to the sand in the water and what happens once the water is dumped out. Repeat the experiment using regular sand and compare the results. Discuss why regular sand becomes wet and why treated sand stayed dry when added to water.
Shaving Cream Marbling
Investigate how the dual hydrophilic and hydrophobic properties of shaving cream can be manipulated to create artwork. Provide students with shaving cream on paper plates. Allow them to add a few drops of food coloring to the shaving cream and swirl it with a toothpick. Watching the colors move on their own allows students to see the interaction that takes place. Discuss what this has to do with hydrophobic and hydrophilic properties. Press a paper card on top of the colored shaving cream to reveal a marbled effect.
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