Seven Layer Density Column Think of it as a Science burrito… email to friend
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Everyone knows that vegetable oil floats on water. That’s because the two liquids have different densities. Density is basically how much “stuff” is smashed into a particular area… or a comparison between an object’s mass and volume. So, the exact same volume of two liquids may actually have different masses, so they would have different densities. That’s why vegetable oil floats on top of water.

But, vegetable oil and water are just one way to explore density. What if you could float seven different liquids in seven different layers? We’ll show you how to be amazing and make a seven-layer density column!

Materials

Light Karo Syrup
Water
Vegetable Oil
Dawn dish soap (blue)
Rubbing alcohol
Lamp Oil
Honey
Graduated cylinder
Food Coloring or True Color Coloring Tablets
Food baster
9 oz. portion cups

Experiment
Video
Related Experiments

Measure 8 ounces of each type of liquid into the 9 oz. portion cups. You may want to start the experiment by coloring each of the liquids to make a more dramatic effect in your column. Light Karo syrup is easier to color than the dark syrup. The only liquids that you may not be able to color are the vegetable oil and the honey.
Start your column by pouring the honey into the cylinder. Now, you will pour each liquid SLOWLY into the container, one at a time. Make sure you pour them in the following order.
- Honey
- Karo syrup
- Dish soap
- Water
- Vegetable oil
- Rubbing Alcohol
- Lamp oil

Note: It is VERY important to pour the liquids slowly and into the center of the cylinder. Make sure that the liquids do not touch the sides of the cylinder while you are pouring. Also, it’s okay if the liquids mix a little as you are pouring, the layers will always even themselves out because of the varying densities.

As you pour, the liquids will layer on top of one another. After you pour in the liquids you will have a Seven-layer science experiment. Density is too cool!

Observations

We've had lots of teachers and scientists help contribute to this experiment. We inadvertently made an error in verbiage in the very first line of our experiment! It's true, vegetable oil and water are close enough in density that they actually don't mix because of the polarity of their molecules, not because of the slight difference in their densities. Oil molecules are non-polar and water molecules are polar, so the non-polar molecules like to hang out with other non-polar molecules and the polar molecules like to hang out with other polar molecules.

Special thanks to Joe F. and Cathy V. for helping us with the correction to our explanation!

How does it work?

Density Chart The same amount of two different liquids will have different weights because they have different masses. The liquids that weigh more (have a higher density) will sink below the liquids that weigh less (have a lower density). To test this, you might want to set up a scale and measure each of the liquids that you are pouring into your column. Make sure that you are measuring the weights of equal portions of each liquid. You should find that the weights of the liquids correspond to each different layer of liquid. For example, the honey will weigh more than the Karo syrup, etc. By weighing these liquids, you will find that density and weight are closely related.

Here are the densities of the liquids used in the column as well as other common liquids:

Have you found a way to make more than seven layers in your column? Let us know, we would love to hear you success story! Email us at webteam@stevespanglerscience.com

Additional Info

So, we've had the density column sitting in our office for a few days now and have noticed a very interesting change... the layers of vegetable oil and rubbing alcohol have switched places. The rubbing alcohol is now below the vegetable oil, indicating that the density has changed. We are not exactly sure why the change occurred.

Since posting this observation, our email box has been flooded with hypothses. Thanks for all of the valuable input we've received! Here are some of your ideas:

Hey science guys -
I have colored vegetable oil using powdered tempera paint. Every year one of the first activities I do with my preschool class is a color mixing experiment. I call over 2 children at a time. I have already dyed 3 small glasses full of water - one each red, yellow, blue - using regular food colors. I also prepare 3 small glasses of veggie oil and dye those the same red, blue, yellow with powdered tempera paint. Then I have one child pick a color of water and the other pick a different color of oil. We pour them into a baby soda bottle half of each liquid. Obviously it doesn't matter which one goes in first since the oil floats. After the cap is securely on, we predict what will happen when we shake it. Then I let the kids each have a turn to shake it and voila! - we have a new color! Of course, after it sits for a while, the misture goes back to the original 2 colors. I leave it out all year - the kids love to go back to those tubes and shake them up just to see what happens!!

Karen I.
Pre K
Children's Circle
Indianapolis Indiana

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As the alcohol in the alcohol solution evaporates what is left is water. This will eventually make the alcohol solution sink down to the water level. Of course by this time the alcohol solution won't really be alcohol but water. So these are my thoughts on the seven layer density experiment. BTW my daughter did something very similar to this for her science project a few years ago. She had bystanders figure out solution was which by looking at the chart for density and seeing which solutions sank and which settled higher.
Cheryl
Mom of 4 (soon to be 5) and
Elementary School teacher

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Likely water has been absorbed by the alcohol layer.
So the question is how to test this hypothesis?
We could use a small pipet to remove part of the alcohol layer and measure the density, but we already know the density changed.
Perhaps we could the color change of cobalt chloride (red = water, blue = no water). I think some silica packing still has the color crystals
to show this change.
Best Wishes,
Mike
West Grand High School

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It would seem the only way for the alcohol to change positions would be for it to change density......if something could be added or subtracted the density could change. If the alcohol is actually a mixture of alcohol and water, then the water and the alcohol could be evaporating from the mixture at different rates, that could change the density. That’s my hypothesis.

Madelon
Arch Ford Education Service Cooperative
Plumerville, AR

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Hi, I just read about the alcohol and vegetable oils switching spots in your density demo. I am not sure this is a guess, but alcohol evaporates at a faster rate than many other liquids, right? I believe the carbon can’t bond to the hydrogen (not sure if that is exactly right, I thought I read that once somewhere), therefore the gas component in it is evaporating. If that’s the case, wouldn’t the liquid being left behind be more compact and have a heavier density?

Hope I’m not totally off base, if I am I will need to get a rag to wipe the egg off of my face…lol. I’d love to know the answer.

Ali (Atomic Ali)
Jacksonville, FL

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Try putting just vegetable oil and rubbing alcohol in a column and then capping the column. The idea here is to exclude water. I think some water may be diffusing into the rubbing alcohol which is usually a 70% solution of isopropyl alcohol in water, and increasing the density slightly.

I think you should rethink your opening statement "Everyone knows that vegetable oil and water don’t mix. That’s because the two liquids have different densities." Oil and water don't mix because they have different intermolecular forces and the oil molecules cannot force water molecules apart in order to mix. Alcohol and water have different densities and yet they mix quite well because they both rely mainly upon hydrogen bonding to hold them next to their neighbors.

Joe
Department of Chemistry
University of Minnesota

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OK, when you add alcohol and water, the alcohol fits in beween the water molecules, right? I wonder if the alcohol simply falls between the molecules of the other substances?

When alcohol and water mix the resulting volume of the two solutions is less than the total of the individual volumes. In this case "one plus one" does not equal two. The reason for this decrease in volume can be attributed to the hydrogen bonds which develop between the alcohol molecules and the water molecules (See "Surface Tension of Water" to see a further explanation of hydrogen bonding). This hydrogen bond pulls the molecules really close to each other and the small water molecules will fit nicely in the spaces between the alcohol molecules.

Having read the reference above, I have revised my thoughts. How about if the alcohol slips through each of the substance molecules, making temporary bonds as it passes down through the column?

- Judith

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Perhaps some of the vegetable oil dissolved into the rubbing alcohol, increasing the density of the new mixture enough that it became denser than the oil. Did something similar happen with the dawn or either sugar and the water layer?

Karen

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Hello Spangler Team!!
Just a quick thought on why the rubbing alcohol and vegetable oil may have changed places in your density column. Rubbing alcohol typically contains acetone, methyl isobutyl ketone, water and denaturants. Some of these compounds evaporate quickly (the acetone, for example) causing the rubbing alcohol itself to change. Since the major compound in rubbing alcohol is water, it makes sense that the density of the rubbing alcohol as it evaporates would change to be very close to the density of pure water (1.00) and making it more dense than the vegetable oil (density 0.91.)

Keep the great ideas coming!!

Karin
8th Grade Science Teacher
Auburn Middle School
Auburn, MA