But let’s get back to green M&M’s. Maybe part of you still believes that the green colour has some magical properties. What if you could scientifically compare the green colour of a Skittle with the green colour of an M&M? You can use a powerful scientific technique called Chromatography, which is the separation of a mixture by passing it through a medium (in this experiment, you’ll use filter paper) in which different parts of the mixture move at different rates. You might have seen chromatography in action if you spilled water on a paper that just came out of an inkjet printer. Chromatography works because different substances in a mixture have different Solubility. Solubility is how much of a particular substance can dissolve in a particular Solvent(a liquid). For instance, you can dissolve a lot of sugar in water, but not quite as much salt. In chromatography, the least soluble substances fall out of the filter paper column first, while the most soluble travel the farthest up the filter paper.
In this experiment you will do chromatography on green M&Ms and green Skittles and compare the chromatography patterns. Of course, you will have lots of extra candy you can experiment with or snack on later.
How are the green colors in Skittles and M&M’s different?
- 2 green Skittles
- 2 green M&M’s
- Aluminum foil
- Pencil (not a pen!)
- At least 2 coffee filters
- Metric ruler
- 2 tall clear glasses or jars.
- 2 mini binder clips (if you don’t have binder clips around, you can use tape)
- 2 straws or skewers (or two more pencils if you are using tape)
- Make your filter paper strips from the filter paper. Measure two rectangles that are 6 cm by 8 cm.
- Carefully cut out the rectangles. The edges should be as straight as possible.
- Using the pencil, write M&M’s on one strip and Skittles on the other strip.
- On the bottom side of strip, use a ruler to find the point 1 cm from the bottom of the paper. Make tiny pencil dots at 2 and 4 cm across. (See diagram 1)
- Study the colour of green Skittle and green M&M, and record any observations and predictions.
- Next, start removing the dye from your candies. Cut out two small (about 2 cm X 2 cm) pieces of foil.
- Place two separate drops of water on top of each of the two pieces of foil.
- Place a green M&M on each drop on one piece of foil.
- Place a green Skittle on each drop on the other piece of foil. Why don’t you want to have the Skittles and M&Ms on the same piece of foil?
- Wait about a minute for the candy colour to seep into the water.
- Dip a toothpick into the tiny pool of green M&M dye. Touch it just above where you made the pencil dot at 2 cm on the filter strip labeled “M&M.”
- Dab another dot at the 4 cm on the same green M&M filter paper.
- Using another toothpick and dip it into the tiny pool of green Skittles dye. Touch it just above where you made the pencil dot at 2 cm on the filter strip labeled “Skittles. “
- Dab another dot at the 4 cm on the same green Skittles filter paper.
- Let the tiny dots dry. This should only take a minute. Repeat dabbing a dot at the same places with the same candy’s dye on the filter paper, and then letting it dry, at least four times. Your chromatography results will be much better if you have thick, tiny dots of each colour. If you are bored while the dots are drying, you can take a taste of the green colors. Does the green colour taste the same in both candies?
- Make the chromatography solution by pouring three cups of water in a bowl, and adding 1/8 teaspoon of salt.
- Pour some salt solution into each of your tall glasses or jars. The liquid should make layer about a one centimeter deep.
- Put a straw or skewer through the triangular centre of each binder clip.
- Clip M&M and Skittles filter papers on each binder clip, with the dye dots on the bottom. If you don’t have mini binder clips, you can tape the filter paper on a pencil. Whatever you do, make sure that your filter papers are hanging straight.
- Hang the filter papers on top of the glass so that the bottom of filter paper is just touching the salt water in the bottom of the glass. Depending on the size of your glass or jar, you might have to add or subtract a bit of salt water.
- Now, watch and wait. The salt water should move by Capillary actionUp the filter paper, carrying the candy dyes with it. (Capillary action describes the upward flow of liquids in a narrow tube or porous material. It is caused by the attraction of the liquid molecules to each other and the tube material.) You should be able to see that there are a couple different colors in the green dye.
- When you see that the wet layer of salt water has travelled ½ cm from the top of the filter paper, remove the filter paper strip from the liquid.
- Set the strips on a clean, flat surface to dry.
- Observe the strips. Try to match the bands you see with the names of the dyes on the candy wrappers.
Results will vary, but you should expect to see bands of both yellow green and blue dyes in the strips. The green M&Ms will show a more prominent blue band.
The colour of the regular M&M is more of a true green, while the colour of a green Skittle is a more yellow green. If you opted to taste the green colors, you probably found that the Skittles dye tasted more sour, probably because the sour Skittle’s interior was also dissolving.
You didn’t want to extract the M&M and Skittles dyes on the same piece of foil because the liquids could have mixed accidently, preventing you being able to tell them apart. That is also why you used separate toothpicks for dabbing.
Your filter paper showed different colour bands because the coloring on the candy shells is a mixture of a couple dyes. The blue bands tended to be higher up on the filter paper because the blue dye was more soluble in the green dye, so it travelled farther up the column before dropping out.
Unless you ate all the leftover candy while doing this experiment, you should be able do several other investigations comparing other colors of candy. If you run out of candy, trying doing chromatography on a black water-based marker. The hidden colors are amazing. Ground-up spinach and other natural dyes are also interesting substances to test!