5 - 12 years
Preparation: 10 mins
Activity: 5 - 10 mins (hands-on), 20 - 75 mins total
* Participants work in pairs/trios
* 1 facilitator per 5 groups
Youtube ID: 9oPymoDJj1s
Each group should be provided:
Customize Activity to Venue
Identify Safety Practices
For each group:
Additional set-up for your specific venue and audience (will vary).
Make Separate a Secondary Color
Direct participants to:
Compare the Color Separation of the Black Markers
Explain how chemists use chromatography to identify the components of the markers (see Explore the Chemistry).
Create Your Own Art (Optional)
Direct participants to:
Here are some key themes to explore with the audience once they've completed the activity. Adjust the details to match the level of your audience.
What is chromatography?
This activity uses an analytical technique called paper chromatography. The word "chromatography," was first used by Russian chemist Mikhail S. Tsvet, who combined the Greek words for "color" and "writing" to describe the technique he used to separate mixtures of colored compounds.
Chromatography separates mixtures of compounds by passing a solution containing the mixture, called the "mobile phase" over a non-moving material, called the "stationary phase." In this activity, water is the mobile phase and the filter paper is the stationary phase.
As the mobile phase moves over the stationary phase, it carries the marker pigments with it. Pigment molecules move at different speeds depending on the size of the molecule and how attracted it is to the paper vs. the water. These differences cause the pigments to separate.
Separating secondary colors
Primary colors typically use one pigment, but secondary colors are made by mixing many different colors. For example, purple, which frequently relies on the food dyes Red #40 and Blue #1, separates into red and blue on the paper. (You can also use chromatography to analyze food dyes in drinks and candy.)
Separating black markers
All of the different marker brands in this activity look black on the paper, but each company uses a unique mix of pigments. Chromatography reveals which colors combine to make which black marker.
Applications of chromatography
Chemists use a variety of compounds for the mobile and stationary phases to separate and analyze parts of mixtures with chromatography. Tsvet's original work used alcohol for the mobile phase and silicon dioxide to the stationary phase to separate the pigments that give plants their colors and show how they break down in cooler weather.
Chromatography can also be used by law enforcement in crime scene investigations, by art experts to determine original paint pigments in restoration projects, and even when analyzing food.