Today we will observe what happens when water and oil try to mix. We will decide if oil is hydrophobic or hydrophilic?
- Clear Plastic Cups
- Vegetable Oil
- Food Dye
- Alka-Seltzer Tablets
- Wax Paper
- In order to prepare for class I would pre-pour small classes of vegetable oil using clear plastic cups. You want those cups to be about 1/2 full. They need to have enough room for the drops of water to fall down, but not so full that we waste all of our vegetable oil.
- It also might be a good idea to pre-mix your water and food dye in different cups
- Try making the art project yourself so that you can better explain – https://babbledabbledo.com/easy-art-projects-for-kids-watercolors-oil/
Are oil and water both liquids? Or are they solids or gasses? How do you know? What to do they look like? Feel like? Smell like?
Try the first activity!
- Give students a clear plastic cup filled about ½ way with oil (baby oil or vegetable oil). Give them each a pipette, and a small cup of water with a few drops of food color added. Have students experiment with dropping the food color water into the oil. Have them observe, and share their observations. Ask the students to explain what is happening!
- Next, give each student an Alka-Seltzer tablet, broken up into pieces. They should drop the pieces in the cup with oil and water. Again, ask them to observe what happened, and offer an explanation.
Oil and Water Art
- Pass out cardstock to each student.
- Give them clean cups of oil and colored water, or set up stations for oil and water.
- Have the students use their pipette/dropper to drop some colored water around their paper.
- Then, with a clean pipette, have them drop oil in top of those spots.
- Have them observe the reaction between these and what is happening.
- They can use multiple pieces of paper if they wish.
- Allow the one they want to make into art to dry for a few hours or overnight. The reaction between the two liquids will cause a cool art effect!
- Hydrophobic – Water avoiding, or fear of water
- Hydrophilic – Water loving
- Additional InformationWater molecules are polar and one end has a slight negative charge, the other a slight positive charge. The polarity means those water molecules can form hydrogen bonds and attach to other molecules that are also polar, this includes other water molecules. It is like little magnets attracting each other. Polar substances are hydrophilic! They like water.
On the other hand, we have oil molecules which are non-polar. This means they can’t form hydrogen bonds with water molecules. They are hydrophobic! This results in water and oil not mixing and instead bunching together. Instead they stay separate. Because oil is less dense than water, it floats on top, and the colored drops of water sink to the bottom.
When we shake the water and oil mixture you are attempting to emulsify the mixture through a physical process. It breaks down the water bubbles into smaller bits, but it still does not mix and dissolve. When Alka-Seltzer mixes with water it creates a gas. This gas forms bubbles in the liquid and rises to the top, out into the air, because it is lighter. When the bubble forms it will often form around the colored water, causing the colored light bubbles to rise and fall, like a Lava Lamp!