Get ready for all the rainbow heart eyes in this easy and gorgeous introduction to chromatography. 🌈😍 Recommended age 3.5+
This activity focuses on the concept of solubility and how an appropriate solvent can carry molecules along a stationary phase. Read on for some basic science and how to make some jaw dropping art!
- Paper Towels
- Sharpies in several colors
- Rubbing alcohol/ isopropanol
- Eye dropper (can also use a spoon in a pinch)
- Baking sheet or something to protect your table
- Safety glasses (to protect eyes from the isopropanol)
- Cut squares from a paper towel (four from a large sheet or two from a select-a-size sheet).
- Find the center of sheet and using different color Sharpies, heavily color in dots around the center point. Make sure the dots have a lot of ink in them, but don’t puncture the paper towel.
- Using the eye dropper, drop isopropanol onto the center of the paper towel and watch as the ink radiates out from the center. Keep slowly adding isopropanol to grow your chromatograph.
- Use your science art to make new crafts or hang it up to display!
Extra Experiments and Questions
- Try doing this with water instead of isopropanol. Does it work? What’s happening?
- Try doing this with washable markers (like Crayola). Which works better- water or isopropanol?
- Do you think this would work with crayons?
- How does this relate to stain removal? Why can’t you wash Sharpie out of your clothes with water?
- Try putting less ink on the dots and see if you can separate some of the colors within the ink. The success of this will vary on the markers/colors you use, but its worth a shot!
Chromatography is used frequently in labs to separate compounds in a mixture. There are many types of chromatography but they are all based on a similar concept: a mobile phase carries your molecules of interest through a stationary phase, and based on the different interactions with the mobile and stationary phase, the different compounds can be separated. This experiment illustrates how a solvent (the isopropanol) can carry soluble molecules (the ink) through a stationary phase (the paper towel). After kids grasp this concept, you can move on to more delicate examples of chromatography like separating the components of fall leaves or a bouquet of flowers. See below for some key definitions to go over.
Chromatography: A way to separate parts of a mixture by moving the mixture and a solvent (mobile phase) along a surface (stationary phase). Because the different parts of the mixture will “prefer” to be on the stationary phase or mobile phase differently, they travel at differing rates, causing the parts to separate.
Solubility: A demonstration really helps to explain this to kids. They first must know that everything is made up of smaller parts, like molecules, ions, or atoms. Mix sugar or salt into warm water and show them that it seemingly disappears into the water. Explain that the smaller parts are being broken off from the larger crystal and surrounded by water molecules, which keeps them suspended in the liquid. They are still there, we just can’t see them. Then try doing this with chalk or something else that is not soluble in water. They will be able to see the bulk either floating or sinking to the bottom. Explain that these things are insoluble. The sugar or salt have properties that make them want to associate with water, kind of like magnets sticking to each other, while the chalk molecules do not.
In this experiment, the ink from Sharpies is soluble in isopropanol but not in water. The isopropanol is called a solvent, and the ink molecules are called the solute.
Mobile Phase: In this experiment, the mobile phase is the isopropanol. It carries the ink molecules along the paper towel through capillary action.
Stationary Phase: In this experiment, the stationary phase is the paper towel. If solute molecules interact strongly with the stationary phase, they will stick to it earlier than molecules with less attraction to it.
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