20 Minute Labs - Rainbow in a Jar

USING DENSITY TO MAKE A RAINBOW

Isn't it exciting to see a rainbow? The beautiful array of colors is a wonder - it may seem like magic, but we can understand rainbows through science!

Put simply, rainbows occur when white light from the sun bounces off raindrops at a particular angle and splits into all the colors we can see.

In this month's 20 Minute Lab, we'll make our own rainbows using common liquids from your kitchen! Instead of splitting light, we'll make our rainbows using density.

Like real rainbows, this one won't last forever, but it's sure neat while it does.

WHAT YOU’LL NEED

• small clear glass jar (we used a small mason jar)
• honey (generic brands work fine)
• light corn syrup
• blue or green dish soap
• canola or olive oil
• different colors of food coloring
• rubbing (isopropyl) alcohol (91% works best, but 70% will do - it's what we used)
• a small bowl (or multiple bowls if you don't want to clean the same one out a few times during the experiment)
• spoon
• eye dropper
• water

NOTE: the amount of each liquid you use will depend on your jar's size and how thick you want to make the rainbow stripes. For each liquid, you will want to use equal amounts, except for the oil - you will use double the amount. In the Yellow Scope lab, we used half a cup of each liquid and a full cup of oil. 

LET'S GET STARTED!

1. Making sure not to touch the sides, pour the honey into the center of the jar. (If your honey is crystallized, you can scoop some into a small bowl and heat for 20 seconds in the microwave).
2. Pour the corn syrup into a small bowl. Add 2 drops of red and 1-2 drops of blue food coloring. Stir to make the syrup purple.
3. Gently pour the syrup into the jar on top of the honey. (Make sure to pour in the center of the jar, avoiding the sides.)
4. Now add the dish soap, again avoiding touching the sides of the jar.
5. Measure the water into a small bowl and add food coloring. If your dish soap was blue, make the water green by adding 2 drops each of yellow and blue coloring. If your dish soap was green, add 2 drops of blue coloring to make the water blue. Stir to mix.
6. Again, gently add the colored water to the center of the jar.
7. Now add twice the amount of oil to the jar. The bottom half of this layer will be the 'yellow' layer, and the top half will become the orange layer.
8. Measure the rubbing alcohol into a small bowl and 3 drops of red food coloring. Stir to mix.
9. Using the eye dropper, carefully add the rubbing alcohol to the jar. This time you want to squirt the alcohol down the side of the jar. This prevents the alcohol from mixing with the water layer.
10. Being careful to keep the liquid still, hold your jar to the light and admire all the colors!

CONCLUSION

What's going on?

Why don't all the different liquids just mix together instead of forming layers? Well, each liquid has a different density. The different liquids stack on top of each other, with the most dense on the bottom and the least dense on the top. 

Density refers to how much stuff can be packed in a given space. Scientists call the “stuff”, mass and the “space”, volume.

You might remember from last month's 20 Minute Lab, Lava Lamp in a Glass, that some molecules are larger than others. Some liquids are made up of small molecules that are packed tightly together (more dense), while other liquids are made of large molecules that are more spread out (less dense).

Liquids made up of smaller molecules, like water, are more dense and sink toward the bottom. Liquids made up of larger molecules like oil are less dense and don't sink as much. 

In this experiment, you poured the liquids into the jar in a specific order, from the most dense (honey) to least dense (rubbing alcohol). In this way, each new layer stacked on top of the layer below it. You could repeat the experiment and try adding the liquids in a different order to see what would happen!

NOTE: If you used 70% rubbing alcohol (like we did), that means that the other 30% is water. This means that when you added the alcohol, some of it sunk into the oil (creating that orange layer), since water is denser than oil and wants to go underneath the oil layer!

SHARE WITH US!

Let us know what you did. Share your photos and results with us on Facebook, Twitter, Instagram, or send us an email to info@yellow-scope.com. We love getting your messages!

For more exciting experiments, check out our Yellow Scope Science Kits on the Shop tab of our website!