Science Buddies: "Ask an Expert"

Experiment using orange & green M&Ms and Skittles with alcohol as solvent. Orange did not separate at all. Why? Green formed chromatographs 2x and a tie dye effect 3x. Why? Same dye used in both candies but results don't look the same. Why?

Hi Carolyn!

An interesting topic you are doing, it seems. It's a bit unusual that the orange doesn't separate, but my suggestion is that you try to use a different solvent in your experiment. Maybe the alcohol cannot separate the orange color; I suggest that you use water as the solvent (after all, water is the universal solvent).
I am not completeley sure about what you mean when you talk about "dye" and "tie dye effect". What are you using dye for? It might be helpful if you clarify this.

Hope this helps.

I agree with the idea of using a different solvent. You may want do an online search about how paper chromatography works, just so you understand all the variables involved really well. I would also recommend using water as a solvent for your experiment, but if you want to add another level of complexity to your project, I would suggest using polar and nonpolar solvents for your chromatography experiement. I am not sure what grade you are in, but most high school chemistry classes introduce the concept that "like dissolves like", so if the pigments coloring your candy are nonpolar, a polar solvent such as water will be ineffective in separating those nonpolar pigments.

I hope this helps.

Hi Carolyn,

Here is some additional information that will help you get better results. Willz and vtrip have given you the correct advice to try a different solvent, and I think some additional information on chromatography and the chemical characteristics of the dye will help you solve this problem. Molecules will not separate by chromatography unless they are completely dissolved in the solvent you are using for your experiment. The fact that you are getting only one band for orange and a tie dye effect for the other colors suggests that the food dyes are not particularly soluble in alcohol. (I assume you are using isopropanol.) Here is a website that includes a list of solvents based on polarity.

http://books.google.com/books?id=gcCFIo ... YhBiSQsMHM

This is called the eluotropic series. Water is the most polar solvent so it works best for dissolving polar molecules like sugar and sodium chloride. Pentane is the most non-polar solvent and it works best for dissolving non-polar molecules like fats and pesticides.

Food dyes are large organic molecules containing rings of carbon atoms with alternating single and double bonds. Here is a website that shows structures of typical food dyes:

http://icn2.umeche.maine.edu/genchemlabs/Dyes/dyes1.htm

Since food dyes contain lots of carbon and hydrogen, they are relatively non-polar so switching to a solvent that is above isopropanol on the eluotropic series should solve the separation problem. One obvious possibility is acetone, which is found in nail polish remover, so that would be easy enough for you to try. If that doesn't work, then ask your teacher for help in finding another solvent. Remember that non-polar solvents are very flammable, and they should not be used in enclosed areas, so please follow all safety precautions.

One more suggestion. You could contact the manufacturer of M & M's and Skittles and find out what dyes are used for the various colors of candy. That would help you confirm your results.

Please let us know if you have any other questions about the chemistry of your project.

Donna Hardy

I am also planning on doing the candy chromatography for my science fair project. The experiment sheet says to test the Rf value in all the test strips. The problem is that it doesn't say how to do it. I've researched it and haven't found anything.

Please help!

Thanks,

Lydiabob

Hi Lydiabob --

Check out this article:

https://www.sciencebuddies.org/science- ... p006.shtml

It tells you exactly how to measure the Rf value.

--Rajeev

Duh!
Thanks SO MUCH Rajeev! Sorry for wasting your time. I did not think that there would be important information like that in the intro. Now I know and won't waste your time like that again. That is pretty embarrassing ! I know that was breaking the do's and don'ts of the forum.

Again: Thank You!

Lydia

Just in case anybody reads this old post -- my daughter also did the M&M, Skittles, Spree food dye chromatography experiment. After our research, we are pretty sure that the orange candies are just 1 dye -- not 2 as you might assume. Orange is made from one Yellow 6 and Yellow from Yellow 5, or something close to that.