Solve a Chromatography Mystery

Overview

Students will learn about the color wheel and the science of color by solving a crime using ink chromatography!

Experiment Length

30 minutes

day 4

materials
  • 3-4 different types of black markers (e.g. a sharpie, a Crayola marker, and a Papermate marker)

  • Coffee filters or paper towels

  • Cups

  • Water 

  • Popsicle sticks

  • Tape 

  • Scissors

steps

Preparation

  1. Have a parent or sibling write a secret note with one of the black markers on the coffee filter. Make sure your student scientist doesn’t see which marker was used!

  2. Use tape and Sharpie to label each type of marker with a number for easy organization and identification.

Experiment

  1. Cut up your coffee filter 3-4 into long 1-inch strips

  2. Cut a strip from the ransom note that includes some of the writing. 

  3. Draw a medium-sized dot at the bottom of each strip using the different markers you chose for each. 

  4. Make a note of which marker you used for each strip

  5. Tape each of the strips to your popsicle stick such that they don’t touch. Make sure each strip will fit inside your cup without touching the bottom. 

  6. Fill your cups with water until the bottom edge of the filter strips are just touching the water. The dots you drew should still be above the water level.

  7. Wait and observe as the water moves up the strips! (5 mins)

  8. Compare the colors of your resulting patterns with those from the ransom note to determine which marker the thief used to write the note!

  9. Clean up!
     

the science

Chromatography is a technique used to separate mixtures and analyze their components. Since black ink is actually made of many colors, certain colors don’t always stick well to the paper and easily get carried by the water, moving further up the strip and the coffee filter absorbs the water. Think of it as a running race. At first, all the runners are gathered at the starting line, but soon, runners spread out and go faster/slower because of their different abilities. Notice how the coffee filter strips for each marker look different from one another. This is because different types of markers have different combinations of ink pigments in them.

 

Think about why this might be the case. What differentiates a Sharpie from a Crayola marker? Why might these differences affect the ingredients that go into their ink?

Taking it further

Solving crimes is just one of the many ways adults use chromatography in the real world. Environmentalists use chromatography to analyze the components of our drinking water to make sure it’s sanitary. Doctors use chromatography to detect levels of chemicals in a person’s bloodstream. What other experiments can you think of that could involve chromatography? 
 

If you want to take your learning further, watch this Khan Academy video. 

Inspired by webinnate.co.uk

Special thanks to Emily Deng for the Spanish translation

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