I came across a simple, yet interesting experiment that was first described by Elizabeth Sumner Walter in 2001. She merely had students pour water into a dish containing some Gobstoppers candies.
I showed this experiment to some of my college chemistry students while they were working on a different laboratory experiment. Two of my students, Nathan Ford and Rachel Hubbard captured some video of this experiment, except that they substituted M & M’s candies for the Gobstoppers. You can see this experiment below:
The experiment sparked a lot of interest and discussion. Questions and comments ranged from “what is going on?” to “what happens if you use hot water?” and “Why don’t we try adding some soap?!” The most common question I heard was “why don’t the colors mix?”
A few students got online, and found one website on which it is claimed that the colors don’t mix due to a layer of water insoluble wax on the candies. It is claimed that this wax forms a shield that prevents the water soluble dyes from mixing. Indeed, carnauba wax is listed as one of the ingredients in Gobstoppers candy. However, carnauba is NOT listed in the ingredients in M & M’s.
We decided to test the claim that a waxy candy coating prevents mixing. If this is indeed the wax that prevents the colors from mixing, then its presence should be important in seeing this non-mixing effect. We tested a variety of candies (Gobstoppers, Dubble Bubble Gumballs, Skittles, Spree) that contained carnauba wax. Sure enough, they all showed this non-mixing effect. However, when we tested candies that do not have wax listed in the ingredients (M&M’s) the same effect was observed!
I’m interested in a couple of things regarding this experiment. First, I’m curious as to why this non-mixing effect occurs. I’m wondering if any of you have any ideas why the colors tend to stay in their own particular region in the water. We have noticed that, given enough time, the colors will bleed together. But even after very long periods of time, semi-distinct regions of colors are observed. Second, I’m wondering if any of you have any ideas for modifications on this experiment, and how these modifications might be used to illustrate chemical principles. For example, I have found one video online which shows that the temperature of the water affects the rate at which the dyes spread out from the candies – what a great way to demonstrate the kinetic-molecular theory!
Editor's Note: See a follow up post where Tom explores this idea further: https://www.chemedx.org/blog/solution-mm-mystery
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For Demonstrations: Please refer to the ACS Division of Chemical Education Safety Guidelines for Chemical Demonstrations.
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