4 Science Experiments for Leftover Halloween Candy

What to do with all that leftover Halloween candy? Here are four easy science experiments to explore chromatography, acidity, osmosis, and density with candy.

Sabrina Stierwalt, PhD
5-minute read
Episode #168

The jack-o-lantern candles have gone out, the costumes have been discarded, and the spooky décor has been stashed away for next year, but you are still left with the spoils of trick-or-treating: heaps of leftover Halloween candy. Instead of eating it all, why not use it for some science?


The process of separating and analyzing the components of a mixture is known as chromatography. Chroma is the Greek word for color and what is more colorful than candy?! Often what appears to be a single color dye, especially for brown or black candy, is really a mixture of several different colors. Anyone who has seen their kids mix many vibrant colored mounds of play dough together to form one unsatisfyingly brown blob knows this to be true.

Separating the colors in candy only takes a few household items. A great duo to start with is a brown M&M and a brown Reese’s Pieces. They both appear to be the same color brown, but as we will see, the colors that blend together to create that brown are very different. First, dip the candy in water and then use it to paint a stripe about two inches from the end of a strip of coffee filter paper. You may need to do this several times to get a good, clear line. Alternatively, if you find this to be too difficult, instead wet the candy and run a creased filter over top of it to make the line.

Next place the very tip of the filter strip in a glass of water so that your brown candy streak is just two inches or so above the water line. As the filter absorbs more and more of the water, the moisture will travel up the filter toward your mark. (This could take a few minutes, so you’ll have to be patient.)

As the water climbs up the filter, it will carry the dye with it. Lighter components will be able to travel farther while the heavier components of the dye will get left behind. What differences do you see between the chromatography results for the two candies?

Acids and Bases

When you taste something as sour, that is your brain’s way of telling you that you are eating something acidic. Acids are substances that will donate their hydrogen ions when dissolved in water. (Note that bases are the opposite of acids: they will accept hydrogen ions when dissolved in water.) Acids are defined as having a low pH and produce carbon dioxide gas when they react with carbonates (a kind of salt that consists of a carbonate ion).  

An example of a carbonate that you likely have lying around the house is sodium bicarbonate, which also goes by the name of baking soda. Fill a few cups with water (it helps if the cups are clear so that you can see the reaction better) and drop different kinds of candy in each one. Sour candy like Nerds and Sweet Tarts work well for this experiment. Then add a spoonful of baking soda. Since these candies are sour, they are highly acidic and the resulting reaction will produce bubbles of carbon dioxide gas.

Which candies make the most bubbles? If you crush the candy first, does it speed up or slow down the effect?


About the Author

Sabrina Stierwalt, PhD

Dr Sabrina Stierwalt earned a Ph.D. in Astronomy & Astrophysics from Cornell University and is now a Professor of Physics at Occidental College.