Candy chromatography is a type of paper chromatography that is easy, inexpensive, and fun. The basic materials are colored candies, water, and coffee filters. The process separates the pigments in the dyes that color the candies. Here are two sets of candy chromatography instructions. The first targets young children and raises interest in science and exploring how things work. The second set of instructions introduces paper chromatography at the high school or college level.
Candy Chromatography for Kids
Explore color chemistry with this basic candy chromatography project.
- Colored candies
- Water
- Paper coffee filters
- Separate the coffee filters and place them onto individual plates.
- Place a single colored candy in the middle of a coffee filter.
- Add a drop of water onto the candy.
- Watch as the dye from the candy spreads outward from the center and separates into its component colors.
Tips
- Good candy choices are the ones coated with a shell, like Skittles and M&Ms.
- Green, purple, orange, brown, and black candies are the ones most likely to contains multiple pigment colors. Blue, yellow, and red candies (the primary colors) often only contain one pigment an may not be very exciting for children.
- For more concentrated color, first group candies according to color. Place one or more candies of a single color onto a plate or strip of aluminum foil. Add a few drops of water. Then, drip the resulting colored droplet onto the center of a coffee filter. Repeat with other candy colors. If you like, make custom color mixtures so kids can separate them (e.g., red + yellow = orange; blue + yellow = green; red + blue = purple). This step also reduces the risk of muddying up the colors with chocolate or whatever might be beneath the outer candy shell.
How It Works
The basic principle is that water carries the dissolved pigments into the paper and it’s easier for small pigments to navigate the fibers in the coffee filter than it is for larger pigment molecules. Some food colorings only contain one kind of dye or pigment, so the resulting image (the chromatogram) is just a ring of a single color. Other colorants actually consist of multiple dyes. The chromatogram from these candies shows rings of different colors.
- See if children can predict the colors of the pigments in a candy.
- For chromatograms with multiple rings, see if they can identify which ring represents the smallest pigment (the color that travels the farthest) and the largest pigment (the one that travels the least distance).
- If you like, introduce more complex concepts. Chromatography separates molecules according to multiple factors (not just size). Cellulose in paper is polar, so some pigments bind to it or are attracted by it. So, whether a pigment is polar or nonpolar or whether it carries an electrical charge also determines its movement through the paper.
Candy Chromatography for More Advanced Students
Although candy chromatography is simple, it actually introduces most of the basic terms and concepts of chromatography. Slightly changing the design makes it possible to directly compare the pigments in different candies or to compare candies against a standard mixture of dyes.
- Colored candies
- Coffee filters or filter paper
- Water
- Table salt
- Toothpicks
- Plate or foil
- Tall glass
Procedure
- First, cut the coffee filter or filter paper into rectangular strips. Each strip will form one chromatogram.
- Using a pencil, draw a line 1 cm or 1/2″ from the end of each strip. Place pencil dots for each candy color in the test. Label the dots.
- Place colored candies on a place or piece of foil. Separate the candies according to color and leave space between them so they don’t touch. Drip water onto each candy so you get a spot of dyed liquid around each one.
- Using a toothpick, pick up a droplet of color and place it onto the labeled dot on the paper. Try keeping each dot as small as possible. It helps applying a tiny dot, letting it dry, and then applying more color. Repeat the process using other colors, using a clean toothpick for each color.
- Prepare a 1% salt solution. Mix 1/8 teaspoon of salt with three cups of water (1 milliliter or cm3 of salt and 1 liter of water). Shake or stir the solution until the salt dissolves.
- Pour the salt solution into the bottom of a glass so the liquid level is 1/4″ or 0.5 cm. Basically, make certain the liquid level is below the pencil and sample line on the paper.
- Stand the filter paper in the glass so the pencil line is above the liquid level.
- Remove the paper when the liquid level is 1/4″ or 0.5 cm from the end of the paper. Mark this location with a pencil so you will know how far the solvent progressed through the paper. Set the paper aside so it dries. This is your chromatogram.
After the paper dries, compare the results for different candy colors. Do any candies contain the same dyes? You can tell because these bands are the same color and distance along the paper. Which candies contain multiple dyes? A candy that contains multiple pigments has bands or lines that are different distances from the pencil line.
How Candy Chromatography Works
In this project, the paper is the stationary phase. It does not move, but it separates the components of the mixture. The paper is cellulose, which is a polar molecule. So, the pigments move at different rates through the paper based not only on size and shape, but also by polarity and electric charge. The salt water is the mobile phase. It carries the sample through the stationary phase in a definite direction. The liquid phase moves through the stationary phase via capillary action, which depends on surface tension, adhesion, and cohesion.
One way of analyzing a chromatograph is according to Rf values. An Rf value is the distance traveled by the sample component divided by the distance traveled by the solvent. The Rf value makes it easier comparing different components of a sample and also has some use when comparing the results of chromatograms made at different times.
Further Investigation
- Compare the effect of the composition of the fluid phase. For example, compare what happens if you use water or ethanol instead of salt water.
- Consider sample solubility. What if you repeat the project using organic dyes instead of water soluble colorants? What solvent should you use?
- Repeat the project using food coloring, marker ink, or other colorants.
- See what happens if you change the solid phase. What are the results replacing the coffee filter with a paper towel or strip of cotton?
Chromatography Terms and Definitions
- Chromatography: Chromatography is a physical separation method. Components separate into the stationary phase and mobile phase.
- Chromatogram: A chromatogram is a physical representation that measures the movement of solvent and sample over time.
- Chromatograph: A chromatograph is the apparatus that performs chromatography. When used as a verb, to chromatograph a sample is to separate it using chromatography.
- Stationary Phase: The stationary phase is one of the two phases in the chromatography system. For example, in candy chromatography, the stationary phase is the coffee filter paper.
- Mobile Phase: The mobile phase is the fluid that moves in a definite direction. For example, in candy chromatography, the water or salt water is the mobile phase.
- Sample: The sample is the mixture that the chromatograph separates into components. For example, the sample is the candy dye in this project.
- Solute: The solute is another name for the sample.
- Solvent: The solvent is another name for the liquid phase.
- Standard: A standard is a mixture of known composition. Comparing the sample against a standard helps identify components of the mixture.
References
- Ettre, L.S.; Zlatkis, A., eds. (2011). 75 Years of Chromatography: A Historical Dialogue. Elsevier.. ISBN 978-0-08-085817-3.
- Ettre, L.S. (1993). “Nomenclature for Chromatography (IUPAC Recommendations 1993)”. Pure and Applied Chemistry. 65 (4): 819–872. doi:10.1351/pac199365040819
- Haslam, Edwin (2007). “Vegetable tannins – Lessons of a phytochemical lifetime”. Phytochemistry. 68 (22–24): 2713–21. doi:10.1016/j.phytochem.2007.09.009
- McMurry, J, (2011). Organic Chemistry With Biological Applications (2nd ed.). Belmont, CA: Brooks/Cole. ISBN 9780495391470.
- Ninfa, A.J. (2009). Fundamental Laboratory Approaches for Biochemistry and Biotechnology. ISBN 978-0-470-47131-9.