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Zipper-lock Bag Variation to show a chemical reaction

1. Fill three, quart-size zipper-lock bags with approximately 1 tablespoon of baking soda.
2. Fill three, snack-size zipper-lock bags with varying amounts of vinegar.  For example, fill one bag with 60 mL (1/4 cup) of vinegar, the next bag with 80 mL (1/3 cup) of vinegar and the last bag with 120 mL (1/2 cup) of vinegar.
3. Seal the vinegar bags and place them in the bags with the baking soda.
4. Make sure the baking soda bags are tightly sealed and put on your safety glasses.
5. Put the bags on a table where it's okay for things to get a little wet and messy (maybe even outside).
6. Now get ready for the fun... Punch the vinegar bags inside the baking soda bags to break them open and then shake the baking soda bags to make sure the substances mix.
7. Make observations about how large each bag gets and how long it takes before you hear the giant POP!

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

• 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?

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 (measured in g/cm3):

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

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

www.washoe.k12.nv.us/sunvalley

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