Key Concepts
Chemistry, dyes, food coloring, chromatography, solubility

Introduction

Do you have a favorite M&Ms or Skittle candy color?  Have you ever wondered what dyes are used to make that particular color?  Some candies are the color they are because of a single food coloring, while others may use a couple different dyes to create just the right appearance.  In this activity you’ll get to do some scientific detective work at home to investigate which colored M&M’s candies use which dyes.  If you have some M&M’s leftover from Easter, this is a way to put those candies to good, scientific use!

This activity is not appropriate for use as a science fair project. Good science fair projects have a stronger focus on controlling variables, taking accurate measurements, and analyzing data. To find a science fair project that is just right for you, browse our library of over 1,200 Science Fair Project Ideas or use the Topic Selection Wizard to get a personalized project recommendation.

Background

If you’ve ever seen a drop of water hit a print-out from an inkjet printer, you know that when this happens the ink starts to run.  The water is absorbed into the fibers of the paper by capillary action.  As the water travels through the paper, it picks up ink particles and carries them along.  This same process can be put to good use as a technique called paper chromatography.  

Chromatography includes a group of techniques that are used to separate various components in a complex solution.  In each chromatography apparatus, there is generally a mobile phase (which is a fluid the components are dissolved in) and a stationary phase (which is the material the fluid moves through).  For example, in paper chromatography, water is the mobile phase and paper is the stationary phase.  The solution’s components ideally move at different speeds as they travel through the stationary phase so that they can be separated.  In paper chromatography, different pigments can be separated based on their solubility.  A pigment that is more soluble than another will generally travel farther because it’ll be easier for it to dissolve in the mobile phase and be carried with it along the paper. 

Materials

  • Paper towels. Thicker ones will work better.  
  • Scissors
  • Pencil
  • Large bowl or pot
  • Measuring spoon
  • Measuring cup
  • Water
  • Salt
  • Large jar with a narrow opening
  • Medicine dropper
  • A clean plate
  • M&Ms, one of each color you want to test.
  • Timer or clock
  • Red, green, and blue food coloring
  • Clothespins
  • Drying rack (optional)

Preparation

  1. Cut the paper towels into strips that are each about one inch wide.  Make each strip at least one inch longer than the height of your large jar.  Cut three strips for the food coloring samples and an additional strip for each M&M color you want to test.
  2. Use a pencil to label which candy color or food coloring will be spotted on each paper strip.
  3. Draw a pencil line about one inch from the bottom end of each paper strip.  
  4. In a large bowl or pot, mix together 1/8 teaspoon of salt with 4 cups of water.  (To get approximately 1/8 teaspoon you can fill a ¼ teaspoon measuring spoon so that it is half full.)  Pour a small amount of the salt solution into a large jar with a narrow opening so that the jar is about one inch full. 

Procedure

  1. Put a single drop of water on the clean plate.  Set an M&Ms candy in the drop of water and leave it there for three minutes.
  2. After three minutes, flip the candy over so its other side is in the drop of water.  Leave it there for another three minutes.  Then remove the candy.
  3. Take one of the paper towel strips you prepared and place the pencil line you drew on top of the now-colored drop of water.  Do you see the dye soak into the strip, coloring the area around the line? You can get some extra dye on the line by dabbing the sides of the wet candy with it.
  4. Repeat these steps with the other M&M colors you want to test, using a new strip for each M&Ms candy.
  5. Next prepare a strip for each food coloring.  Put a small drop of food coloring on the plate and lightly dab the line on a new strip against it.  Repeat this so that you have three food coloring strips (one each for the red, green, and blue food coloring).
  6. Carefully put the pigmented end of a strip into the jar you filled with salt water.  Put the strip into the jar until the strip just touches the salt water.  Drape the top of the strip over the jar’s opening and secure it with a clothespin.  Make sure that each strip is not touching the jar’s sides, but only contacts the jar where it is secured.  Place and secure as many of the other strips as will fit in the jar, being sure that they do not touch the jar’s sides or each other.
  7. Let the water rise up the strips until it is about an inch or two from the top.  Remove the strips at this point.  (This may take around 10 minutes.)  What has happened to the colors on the strips? Keep a close eye on the strips and where the water is – if you let the strips run too long, the water can reach the top of the strips and distort your results. 
  8. If you could not fit your other strips in the large jar, put them in the jar now, as you did with the other strips, and run them until they are similarly done.
  9. Let the strips completely dry out.  You can set them on a drying rack, or on the clothespins laid flat, to do this.
  10. Look at your strips.  How many dye components does each M&M color have? Can you identify which dyes that are in the food coloring are also likely in the M&Ms candies? Do your results make sense to you?  

Extra: A more accurate way to identify colored components in a solution using paper chromatography is by determining their retention factor (Rf value). The Rf value is the ratio between how far the component travels and the distance the mobile phase (solvent) travels from a common starting point (the line you drew on the strips).  If other conditions are kept the same, the Rf value for a certain component should be consistent.  You can do this activity again but this time measure these distances and calculate the Rf value for each component.  Based on the Rf values, can you identify which dyes are used in the different colored M&M candies by comparing them to the known food coloring dyes?

Extra: In this activity you used M&M candies, but you could try it with other colored candies as well, such as Skittles.  Does the red in Skittles look the same as the red in M&Ms when you test both using paper chromatography? What about their other colors?    

Extra: You could try this activity again but this time compare using different kinds of mobile phases (e.g., salt water, water, vegetable oil, isopropyl rubbing alcohol, etc.).  Does a dye travel different distances depending on the mobile phase you use?  What do you think this tells you about the solubility of that dye in the different mobile phases?

Observations and Results

Did you find that green and brown M&Ms are made up of two dyes, while blue, yellow, and red M&Ms only use one dye?  Did some of these dyes match the ones from the red, blue, and green food coloring strips?

You may have seen that blue food coloring has blue and red dyes, red food coloring has two different red dyes, and green food coloring uses a blue and a yellow dye (the yellow may be covered by the blue dye, making it appear green, and all of this can depend on the exact food colorings used).  Looking at the ingredients list on the packaging can help you determine exactly which FD&C dyes these are.  Blue M&Ms use one of the same blue dyes and red M&Ms share one of these red dyes (you can figure out which by looking at their packaging).  If you tried brown M&M’s, you probably saw that they contain a red dye (the same one as red M&M’s) and a blue dye. Green M&M’s also use two dyes, a yellow dye and a blue dye, although the latter may be too faint to easily see.  Yellow M&M’s use a yellow dye.        

Cleanup

  1. If you want, you can eat the wet M&M’s candies!

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Credits

Teisha Rowland, PhD, Science Buddies

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Key Concepts
Chemistry, dyes, food coloring, chromatography, solubility
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