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In this issue:
Chromatography is one of the simplest techniques for separating the individual components of a mixture. In chemistry, a mixture is a combination of substances that can be separated because they are not chemically bonded. (As opposed to a compound, which has elements chemically bonded together.)
In paper chromatography, a mixture is dissolved and pulled across a piece of paper. The mixture separates because its components travel across the paper at different rates, based on their attraction to the paper or solubility in the solvent.
The word "chromatography" comes from the two Greek words for "color" and "writing." Once you try out the fun projects below, you'll see why that's such a fitting name!
>> Watch our chromatography video to see this cool process in action!
Color Hide-and-SeekIs black really black? Let’s start with some simple paper chromatography to find out.
What to do:
As the water travels up the paper strip, it dissolves the ink and pulls it up the paper too. The black ink is actually a mixture of several different pigments, or coloring agents. Some pigments dissolve in water easier and are pulled with the water farther up the paper. Others are more attracted to the paper and move more slowly. Usually smaller molecules will move farther than larger ones. What colors do you see on your chromatogram? Was the black marker really black?
The three primary colors used when mixing dyes or paints are red, yellow, and blue. Other colors are often a mixture of these three colors. Try running a chromatography test again with non-primary-color markers, like purple, brown, and orange. See what hidden colors are really there! You can also try using other solvents, such as rubbing alcohol or nail polish remover, especially for permanent pens and markers that won't dissolve in water.
Fall Colors in Summer LeavesEvery fall we watch amazing chemistry color changes happen all around us. Trees that were green all year suddenly become bright yellow, orange, red, or even purple! How does this happen?
Leaves contain different pigments, which give them their color. Green chlorophyll, which is essential for photosynthesis, is the most common type of pigment, but there are also cartenoids (yellow, orange, brown) and anthocyanins (red). During the summer months, the leaves are so full of chlorophyll that green overpowers any other colors present in the leaves, such as yellow and orange. In the fall the days start to get shorter and the temperature drops, signaling to the tree that it is time to go into storage mode for the winter. The chlorophyll starts to break down, causing the green in the leaves to disappear, and allowing us to see the colors of the other pigments, which were present all along.
You can use chromatography to find out what pigments are present in a leaf when it is still green.
What to do:
Read our article to learn more about how leaves change colors in the fall.
More Fun Chemistry Projects
Learn more about plant chromatography and watch an animation of the process in this online activity.
Explore the nature of color with this beautiful and informative web exhibit: Causes of Color.
Check out this site to see how all colored printing is really made from just four colors.
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