An exploration of chromatography, colors & the movement of molecules
Grade Level:
K-12
Subjects:
Physical Science:
Structure and Properties of Matter
Forces and Interactions: Push & Pull
Molecules: Structure & Movement
Light Waves: Refraction & Reflection
Tools & Materials
Small clear cup(s)
White coffee filters
A variety of black markers (different brands such as Crayola, Expo, Mr. Sketch)
Pencil
Water
Scientific Notebook
To Do & Notice
1. Question: Is the color black really black?
2. Make a Claim:
What do you think the color black is made out of? Is it simply black, or is it a blend of other colors?
3. Testing Ideas:
Choose one black marker to test first. Draw a small circle close to the center of a coffee filter with that black marker. See image for detail.
Next, fold the coffee filter in half and then in half again, creating a cone shape.
Use a pencil to label the outer edge of the coffee filter with the marker brand name you are testing.
Fill a small clear cup with about half an inch of water.
Pull apart the coffee filter so that it can balance on the cup and place the tip of the coffee filter in the small amount of water at the bottom of the cup. See image for detail.
Management tip: the water level should be low enough that it does not touch the black circle you have drawn, the water should only be touching the white tip just below your circle
Set aside and wait for approximately 20-30 minutes while the water absorbs through the coffee filter. Does the water carry the ink as it is absorbed? Does the ink remain black?
4. Analyze & Interpret Data:
Do you see any other colors on the coffee filter besides black? Which colors do each of the marker brands use to create the color black? Are any of the marker brands more vibrant than others? Is there a pattern to the order of colors that separated? (Example: Did blue separate before other colors? Or travel the furthest on the coffee filter?) Return to your claim and think about what you have observed during this experiment. Is black really black?
5. Communicate Findings:
Share your results with SWEP by sending us photos or videos of your experiment or the art you create with your coffee filters (see art ideas below). Post your photos on social media and tag us @sweptahoe on Instagram and/or to @swep4 on Facebook. Be sure to hashtag and follow #SWEPsnippets. If you cannot post directly yourself, send your photos or video to SWEP (Jenna@4swep.org).
What’s Going On
What is Chromatography?
Chromatography is a way of separating a mixture of chemicals in a gas or liquid form by letting them creep slowly past another substance, which is typically a liquid or solid. So, with the ink and coffee filter trick for example, we have a liquid (the black ink) dissolved in water creeping over the surface of a solid (the coffee filter).
Colors Explained:
Primary Colors: The three colors that are called primary colors are red, blue and yellow. The fundamental rule that makes them primary is that they cannot be made by mixing other colors together.
The Color Black: When multiple color pigments are combined, a shade of black appears. A black object may appear as black, but it contains all the other colors that have collected together. Black absorbs light, while white reflects light. Black pigments are made from a combination of other pigments that, when combined, absorb most light.
Molecules on the Move:
We see a variety of colors separating from the black center of the coffee filter because different molecules have different characteristics that cause them to move or behave in different ways. For example, heavier molecules move faster and lighter molecules move more slowly.
Resources
“Explain That Stuff” breaks down how Chromatography works: https://www.explainthatstuff.com/chromatography.html
Watch this video to learn more about the Science Behind Chromatography
Watch this video to learn how you can use 3 primary colors to create black: https://www.youtube.com/watch?v=eHSo3Svqnao
Going Further
Make fun craft projects with the (now colorful) coffee filters used in your experiment:
How to make Flowers
Chromatography Butterflies
Learn more about the science of chromatography - head outside and gather a variety of leaves and try this experiment: Leaf Chromatography
Sing a song with your children all about chromatography https://www.youtube.com/watch?v=idgF61hs65o
Thanks to our partners at Excellence in Education for supporting STEAM based experiments.
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