Flower Petal Chromatography

 

This is a quick easy science project you can do with children of all ages. You can make it very simple for young ones, or more complex for older children. In this project, you crush flower petals with a household solvent, then separate the colorful components of the petals using paper chromatography.
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What is Chromatography?

The word chromatography describes any method that can separate components of a substance by dissolving the substance in a mobile phase (a liquid or gas, called a “solvent”), then passing that mobile phase through a stationary phase (a solid, like paper). The separation happens because as the various components are carried by the mobile phase, they begin to interact with the stationary phase. If a component is very attracted to the stationary phase, it will slow down and not travel as fast as the rest of the mobile phase because it is spending a lot of time “stationary” on the stationary phase instead of being “mobile” in the mobile phase. Components that are not attracted to the stationary phase will travel as fast as the mobile phase. Therefore, when you stop the flow of the mobile phase, the components will be separated based on how much they have interacted with the stationary phase, which is related to how far they have traveled.

For an analogy, say you had a bunch of strawberries in a row on the floor (your stationary phase) stretching across the room. Then, you let three babies (the components in the mobile phase) crawl along the row of strawberries. A baby who doesn’t like strawberries will just crawl on by and not eat anything. This is kind of like a component traveling with the mobile phase that has no attraction to the stationary phase. A baby who really likes strawberries will stop and eat almost every one. This will slow down their pace compared to the other baby. The third baby kinda likes strawberries but not much, and stops to eat only some of them. That baby will have a pace somewhere in between the two other babies. If you freeze frame the babies before the fastest one reaches the end of the strawberries (stationary phase), you have just separated the babies based on their attraction to strawberries. In chromatography, you separate molecules based on their attraction to a stationary phase, where instead of strawberries, you use things like silica or antibodies.


Flower Petal Chromatography

The protocol I did below was the one I did with my two year old. At the end, I’ve included examples of other projects you can do with older children.

Supplies

  • flower petals
  • household solvent like acetone (some types of nail polish remover), ethyl acetate (other types of nail polish remover), or isopropanol (rubbing alcohol). I recommend acetone.
  • Mortar and pestle (or some other way to crush the petals, like a spoon and bowl, or rock and bowl) Fox Run 6240 Porcelain Mortar & Pestle, White
  • Filter paper (the kind I have and is available on Amazon Filter Paper, Qualitative, Medium, 18cm) (*coffee filters will not work well for this project)
  • A glass container like a mason jar or drinking glass
  • Something to cover the top of the glass container (like a coaster)
  • Tape

Safety

This project uses household solvents. You and the kids should wear eye protection and work in a well ventilated room or outside. Do not get the solvents in your eyes or mouth, and follow the instructions on the bottle for appropriate handling. Do not work near an open flame. Read all the instructions before you begin.

Procedure

1. Gather a few flower petals of varying colors.

2. Make note of the colors on a piece of paper by drawing and describing the petals with your kids. They can try to match crayon/pencil colors with each petal, too.
3. Cut your filter paper into a rectangle shape that will fit in your glass container.
4. Depending on your glass container, you will have to figure out how to suspend the filter paper from the top of the glass so that only the bottom of the paper just touches or just hovers over the bottom of the glass. Try
using a pencil and tape to suspend the paper. The paper should not touch the glass on the sides, otherwise the solvent will just run up the side of the paper.
5. (The solvents come into play now, so if your child is young, make sure they can’t touch or play with any of it, but can just see what’s going on. My daughter just sat on the other side of the island and watched while I narrated.)
Put the petals in the mortar and add about 1/2 tsp of
your solvent.
6. Carefully crush the petals until the solvent is a bright, saturated color.
7. Dip a spoon or toothpick into the solvent to pick up just enough to make a line about a centimeter above the bottom of the filter paper. Be careful not to put too much on. If you don’t put enough (the spot or line is faint), just wait until it dries and put more right on top of the first spot. (In the picture to the right, our paper has a little too much! The line/spot is too large. You ideally want it skinnier, but it will work fine, you just
won’t get defined bands.)
8. With pencil (not pen!), mark where your line/spot is. This is called the origin.
9. Pour  solvent into your glass container to come up to about 1/2 centimeter. It needs to be enough that your paper will dip into it, but not so much that the level touches your spot/line of petal extract.
10. Suspend your paper in the glass so that only about 1/2 centimeter is in the solvent (and not any of the colored extract).
11. Cover the top of the glass if possible.
12. Wait until the solvent travels about 3/4 up the paper, then take it out, mark with pencil where the solvent ended (called the “solvent front”), then let it dry.
13. Look over the paper (now called a chromatograph!) and see your separated colors! Compare them to the colors of the original flowers. Was the solvent you chose able to separate them all?

Extra Credit

For older children who seem to have a grasp on the concept of paper chromatography and that flower petals and vegetables are colored by combinations of different molecules, you can try these other experiments with them.
  • Try several different solvents to see how the chromatograph changes.
  • Do this procedure with different vegetables and compare the results. If you want to get technical, you can calculate the retardation factor (Rf value) by measuring how far a component traveled from the origin (that you originally marked with pencil) and dividing that by how far the solvent front traveled from the starting point. Take that number to two decimal places, then compare Rf values of similar colors from different vegetables to serve as evidence that they are the same compound. (To compare Rf values, you have to use the same mobile phase/ stationary phase combination to be valid, so don’t use different solvents here.)
  • Do this procedure in the fall with different colored leaves from the same tree. Do green leaves have orange and red compounds in them? Do orange and red leaves have green compounds?

I hope you get a chance to try this with kids, or even just by yourself! Tell me how it goes or send a picture on social media!
Enjoy!

2 thoughts on “Flower Petal Chromatography

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