Jessica Blindt

Floating Spheres

Science Concept: Density and Polarity

All liquids have density. Some are more dense than others. When a liquid is sandwiched between a more dense liquid and a liquid less dense, it floats between the 2 layers.

Materials:

1. 100 mL glass graduate cylinder

2. water

3. food coloring

4. rubbing alcohol

5. oil

6. eye dropper

Directions: Fill the cylinder halfway with water. Then add a few drops of food coloring. Tilt the cylinder and slowly add the alcohol until 30-40 mL have been added. Be very careful while doing this step. Do not jiggle the cylinder. It works best to slowly dribble the alcohol down the spout side of the cylinder. Using the eyedropper, add 6-10 drops of oil and repeat several times. The oil spheres should drop through the alcohol but float on top of the water.

Introduction: Has anyone seen or eaten taco dip before? Taco dip has different layers of things that sit on top of each other and don't mix. Water and alcohol are like that. When we put alcohol on top of water, they don't mix. What do you think the oil will do? Stay on top? Sink? Let's find out.

Explanation: If done correctly, the alcohol will stay on top of the water and not mix. The oil sinks through the alcohol because the oil is denser than the alcohol. But it is less dense than the water so it floats on top of the water layer. It stays in between the 2 non-mixing layers. Food coloring helps us to see the 2 layers. The alcohol is the key here. If some alcohol breaks into the water, the layers are broken and the oil won't sit between the two. The oil being sandwiched between the water and alcohol shows its density. Polar properties also come into play. Water and alcohol are polar but oil is non-polar. Since both water and alcohol are polar, you must not mix them since like dissolves like. Because the oil is non-polar, it will not mix with the alcohol and water.

Safety: Be careful with the alcohol, especially during the pouring into the cylinder.

Waste Disposal: Dump all liquids into the sink and discard the oil.

Reference: Unknown