Chromatography

Give your students a fun and engaging activity that explores the process of chromatography: a process used in the field of forensic science to separate and analyze chemical mixtures. This activity can be used to teach chemistry or forensic science and is a great way to present a mystery to your class.

Grades: 3-5

Background

Chromatography is the chemical separation of a mixture through a medium as a way to analyze their chemical components and ingredients. The practice is widely used in forensic science and pollution monitoring to identify and analyze different chemical mixtures and substances.

For this activity, you will provide students with the opportunity to use chromatography to chemically separate the ingredients used to make a permanent marker. Each marker will reveal a different pattern and color scheme since they use different ingredients in different proportions to make them.

A great way to introduce this activity if you are including the forensic science concept is to introduce a mystery. Tell the class that a criminal has used a marker to write a note but the brand of the marker is not known. The class can use chromatography to identify the brand of marker that was used to write that note.

What you’ll need

  1. 3-4 different brands of permanent markers
  2. coffee filters cut into short strips (about 3 inches)
  3. wide-rimmed plastic cups
  4. rubbing alcohol
  5. (optional) Popsicle sticks and tape

Activity Procedures

It is ideal to set up the materials of this activity prior to introducing it to students. The number of cups and strips you’ll need depends on the number of groups you will use and how many students will be in each group. Here I will outline the procedure of completing the experiment and you can decide how you want to organize the activity in your classroom.

  1. Fill a wide-rimmed cup about 1/5 of the way with rubbing alcohol
  2. Take a coffee filter and cut it into strips about 3-4 inches long
  3. Take a brand of permanent marker and draw a thick black line about an inch from one end of the strip
    • Note: it is important that the black line not be at the very end of the strip.
  4. (optional) Take a Popsicle stick and tape the clean end of the strip to the center of the stick. Place the Popsicle stick to lay across the diameter of the cup in order to hold the strip in place. Measure the length from the rim of the cup to the bottom of the cup to ensure that the black line will not submerge into the liquid.
    • Note: It is very easy for the coffee strip to lean to one side of the cup. This will cause some of the color to leak from the strip into the cup of rubbing alcohol.
  5. Dip the end of the strip with the marker into the cup. When you submerge the strip, make sure the line does not come in direct contact with the rubbing alcohol. Doing so will cause the color from the line to spread throughout the cup.
  6. Hold the strip and wait as the liquid crawls up the coffee filter strip. This step will take several minutes.
  7. When the pattern of the marker has emerged and spread through the filter, look closely at the colors and patterns revealed in the strip. The longer you wait, the more you will see of the pattern of colors.
  8. Repeat this steps with a different brand of marker. It is helpful to label the strips with the brand being used on that strip.

What Happened Here?

Chromatography is a great example of the differences between chemical changes and physical changes. The activity here demonstrates a physical change and not a chemical change, as the ingredients used to make the marker are not combined or transformed, but mechanically separated. The ingredients of the marker become mechanically separated as the rubbing alcohol strips the color from the marker. Those colors move and spread across the paper as they become separated, revealing the colors used to make the marker.

This article by Explain That Stuff provides a great in-depth explanation of the process of chromatography and its applications in real-world science. Since this is an activity for 3-5 grade, don’t worry about the little details. Use this activity to focus on the differences between physical and chemical changes as well as the real-world applications of this kind of process.

Discussion Guide

After completing the activity, you can lead your students in a discussion to explore what they observed in the activity and what they learned from it. Here are some questions you can use to guide the discussion:

  1. What did you observe as the alcohol moved up the coffee filter strip?
  2. What caused the colors to separate from the markers?
  3. Why do different marker brands have different colors?
  4. Is what happened here a physical change or a chemical change? How do you know?

NGSS Standards

Performance Expectation:

  • Conduct an investigation to determine whether the mixing of two or more substances results in new substances.

Disciplinary Core Ideas:

PS1.B: Chemical Reactions

  • When two or more different substances are mixed, a new substance with different properties may be formed.

 

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