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March 2019 | Resource Feature
Teaching Essential Concepts … with T-Shirt Chromatography
By Lindsay Davis
Children of all ages love to tie-dye. Who wouldn’t like to, with its pretty colors and cool effects?
That said, I am a firm believer that activities in a chemistry classroom should always have a specific academic purpose, and should not be done just because they are “cool.” So, instead of doing real tie-dye, I do T-Shirt Chromatography with my students. This is a chemistry version of tie-dye, where we take Sharpie markers (which are supposed to be permanent) and expose them to rubbing alcohol (isopropanol). With some simple techniques, this method creates a beautiful, colorful T-shirt while teaching the students about concepts like solubility, saturation, polarity, and intermolecular forces (IMFs).
This activity can be modified for younger children, probably as young as four years old. Younger children can just look at how colors are comprised of different colors. Older children can learn about simple concepts like solute, solvent, and solution. My own version of this activity is geared toward students in a first-year standard or honors chemistry class, so much higher-level concepts will be discussed below.
Figure 1. The first step in the T-shirt chromatography process.
Figure 2. An example of T-shirt chromatography in progress.
Chromatography is an important analytical process that is used in research and industry to separate components of a mixture by color. In chromatography, solutes are distributed along a medium by a moving solvent, and are then separated into their component colors. There are many kinds of chromatography, but all have a few things in common. First, there is a stationary phase (or medium) that may be either polar (attracting polar components) or nonpolar (attracting nonpolar components). In this experiment, the stationary phase is the T-shirt.
The second necessary component is a solvent (the mobile phase) that washes the third component, the solute (the color components in permanent markers), across the fabric of the T-shirt. This solvent has to be a different polarity than the stationary phase. The components of the solute may be more strongly attracted to the solvent or to the shirt, depending on their polarity. As the solvent washes through the shirt, the components of the solute spend some time being absorbed on the T-shirt and some time traveling in the moving solvent. Solubility of the solute is based on that substance’s IMFs illustrating the concept of “like dissolves like” — i.e., polar solutions can dissolve other polar solutions and nonpolar solutions can dissolve other nonpolar solutions. Substances are not just polar or nonpolar; there is a range of polarity based on the strength of the substance’s IMFs.
In this experiment, we will use Sharpie “permanent” markers as the solute and rubbing alcohol (isopropanol) as the solvent.
After teaching the necessary concepts of solubility, saturation, polarity, and intermolecular forces, start by asking the students what happens when Sharpie markers come into contact with water. They will tell you that nothing happens, because they are permanent. This activity really gets the students to think about the term “permanent” — and hopefully, they will come to see that permanence depends on the actual components of the solute and solvent.
Figure 3. An example of a T-shirt that has been used for chromatography many times.
Procedure and technique
- Stretch a single thickness of the cloth of the T-shirt over the top of the beaker. Pull the cloth taut and secure it with a rubber band around the outside of the beaker.
- Select a Sharpie marker and make a shape or design. Fill a pipet with rubbing alcohol. Slowly drip it into the center of the shape. Continue dripping the rubbing alcohol onto the cloth until the solvent has spread to the desired width.
- Allow the wet section of the shirt to dry before putting more ink on it.
- Repeat steps 1-3 on different parts of the shirt using a variety of colors.
- After all of the chromatography patterns have developed, allow the shirt to dry completely.
- Dispose of any excess rubbing alcohol in the sink and wash it down with lots of water. Rinse out the beaker and pipet with water. Clean up your work area and wash your hands.
- At home, you can iron the shirt to help set the inks. Wash the T-shirt by hand. Do not put it in the washing machine, as the color will fade.
- Students should always wear safety goggles and aprons when handling chemicals in the lab.
- Students should wash their hands thoroughly before leaving the lab.
- When students complete the activity, instruct them how to clean up their materials and dispose of any chemicals.
Tips and tricks
- My school pays for me to buy each student a T-shirt. If yours does not, ask each student to bring in one. As long as it is mostly white, the activity will work.
- Student must use at least four colors to be able to analyze their possible differences.
- Designs can be as simple as making dots of color (but be sure to saturate the ink on the T-shirt), or can be as complicated as tying the shirt with rubber bands in the same fashion as real tie-dye. Then students can color on the shirt while it is all tied up, really saturating it with the ink. Once the alcohol has been added, the outcome looks very similar to a real, normal tie-dyed T-shirt.
- It is not about how much surface you can cover with the ink. Instead, it is about how much ink you can saturate in any one spot. The more color in a particular spot, the more spreading of color.
- Students can be as creative as they like. Some can draw pictures; some can write words; others just imitate the example that I show them with dots of color to create colorful pinwheels that look like the backs of CDs.
- When applying the alcohol to the shirt, point the pipet with alcohol in the direction you want the alcohol to travel.
- Do not use the marker to color on wet alcohol, as it tends to dry out the marker very quickly.
- Any receptacle to catch the excess alcohol can be used. I use beakers, since they are readily available in a chemistry classroom.
- Be sure to use a rubber band to pull the T-shirt taut when applying the alcohol — otherwise the color will not spread well.
To download additional resources related to this activity, including essential questions and answers for students, click here.
In my experience, it helps to keep in mind a few common student misconceptions, and look for opportunities to clarify when appropriate. For example, many students use the words “polar” or “nonpolar,” even when they are not referencing molecular compounds. Be sure they understand that “polar” is short for “polar covalent” and “nonpolar” is short for “nonpolar covalent.” Likewise, the concept of “like dissolves like” is important, so try to make sure students cannot only quote the phrase, but also be able to explain what it means, especially as it relates to the concept of intermolecular forces (IMFs). Last, some students have a hard time recognizing that molecules are neither fully polar or nonpolar, but actually fall somewhere on a range of polarity, based on the strength of the molecule’s IMFs.
T-Shirt Chromatography is a fun and creative way to teach several high-level chemistry concepts to students. Students have a choice in what they make, and everyone ends up with a product that reminds them of what they learned and how much fun they had learning it. I conclude the lesson a few days later by taking pictures of the students wearing their T-shirts and either e-mailing the pictures to the students or posting them on my chemistry website provided by my school.
(article cover) Gene_L/Bigstock.com