Saturday, September 17, 2011

Unsociable Liquids

Unsociable Liquids
You may have a bottle of Italian dressing in your refrigerator. Notice how the oil and water don't mix? An how the oil floats on top of the water? Or you may have seen a rainbow of colors on a puddle of water in the grocery store parking lot. That's due to a thin layer of oil from automobiles floating on top of the water. Oil and water don't mix because oil is insoluble in water, and it floats on water because its density is less than that of water.

Make sure you have an adult helping you.
Do not drink any of the liquids!
Do this experiment in a place where it's OK to make a mess.

1/3 cup (80 mL) light corn syrup
1/3 cup (80 mL) water
1/3 cup (80 mL) cooking oil
Food coloring - two colors
3 small glasses - paper cups will do
1 tall, narrow, clear glass or jar
Funnel (optional)
Various objects to test their densities, for example:
small piece of carrot or celery
small piece of candle wax
small cork
small glass marble
small piece of metal like a BB or metal marble
whatever else you might like to try

Measure out the liquids into the small glasses.
Add a few drops of one food coloring to the corn syrup and stir well. Add a few drops of another color to the water and stir. Do not add any food coloring to the oil.
Pour the colored corn syrup into the tall, clear glass. Try not to get it on the sides of the glass.
Carefully pour the colored water down the inside of the glass to avoid disturbing the corn syrup. You may wish to use a funnel to do this.
Repeat step 4 with the oil.
Carefully drop one or more of the objects into the liquids, and see what happens!

What happens as each liquid is poured into the glass?
What happens when various objects are dropped into the liquids? Where do they end up?
What do you think would happen if you poured the liquids into the glass in a different order? Give it a try!

What's Happening?!?
Separate layers: You probably noticed that the liquids did not mix, but remained as separate layers. The corn syrup and water do not mix simply because the corn syrup is so thick. If you stirred them for a while, they would mix, because corn syrup is soluble in water. The oil does not mix with the water because it is insoluble in water. You see that in Italian dressing and in oil on puddles of water.
Top or bottom?: You used the same volume of each of the liquids, but each has a different mass. The ratio of the mass of a liquid to its volume is called its density. The corn syrup is more dense than the water and oil, so it stays on the bottom. Water is less dense than corn syrup, so it floats on top of it. Finally, the oil is the least dense liquid of them all, so it floats on top of the water.
Objects: Where did the various objects end up? Cork is less dense than any of the liquids, so it floats on the oil. A piece of wax is more dense than oil but less dense than water, so it sinks through the oil and floats on the water. A piece of carrot is more dense that water but less dense than corn syrup, so it floats on the corn syrup (you may have to give it a little push through the water layer if it has some oil stuck to it). Finally, a marble or piece of metal is more dense than any of the liquids and goes all the way to the bottom. You can use this "density column" to compare densities of all kinds of things!
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