MnSTEP Teaching Activity Collection > MnSTEP Activities > Investigating Chromatography: Separating Pigments

Investigating Chromatography: Separating Pigments

Sybil Haas
Victoria Elementary School
Victoria, MN
Based on an activities from:
Little Scientists: Learning About Changing Seasons by Dr. Heidi Gold-Dworkin p. 34-7.
Sandwich Bag Science by Steve "The Dirtmeister" Tomecek p.22-4.
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Summary

In this chemistry classroom activity, students will investigate colors used to create a black, water soluble marker. An extension can be done using primary and secondary colored water soluble markers as well as spinach leaves. See attachment for the spinach leaf pigment extraction.

Learning Goals

Students will name the pigments that are used to create water soluble markers and leaves.
Students will raise questions about how colors are created.
Students will design an extension activity using markers based on this chromatography experiment.

Context for Use

This lab activity is appropriate for a 2-3 grade classroom with appx. 20-25 students if you complete it as a whole group. Intermediate may be able to complete it individually or small groups (it depends on your group of students). It is possible to use parts or all of this experiment with a younger or older crowd. Pieces of this activity (or using the independent approach) might be a bit over the heads of primary students but can easily be adapted to challenge or reinforce the scientific method in the intermediate and middle school grades. This would depend on the ability of your students and/or their exposure to the scientific method. I would allow two 45-60 minutes sessions for this activity because of the time needed to walk students through the scientific process. For optimal results, you should allow 24 hours for each experiment to take place. Another vital component to designing an extension activity is to have students exposed to the scientific method frequently.

Materials: water soluble markers (three must be black and of different brands), primary and secondary markers that are water soluble, fresh spinach leaves, fingernail polish remover, alcohol, water, wide mouth porcelain mug, spoon, scissors, coffee filter or paper towel (chromatography paper would work best if it is available to you), toothpick, ¼ measuring cup, rubbing (isopropyl) alcohol, zipper style sandwich bags, and paper cup.

Subject: Chemistry
Resource Type: Activities:Classroom Activity
Grade Level: Primary (K-2)

Description and Teaching Materials

I would introduce this unit using the following picture books: Mouse Paint by Ellen Stoll Walsh or White Rabbit's Color Book by Alan Baker
Previous to this activity, I would have introduced the terms primary and secondary colors. We would have experimented with mixing colors. I would also have shown them how white light can be broken into pieces using a prism (sometimes an overhead works)-AKA "the light spectrum." Introducing my friend, ROY G BIV (Red, Orange, Yellow, Green, Blue, Indigo and Violet), will assist students in naming the colors in the light spectrum. We will also discuss why we see colors. (The color we see is the light wave that is being reflected back to us.) The rest of the color waves are being absorbed by the object. I believe that this activity will be beneficial to my students after they have repeatedly been exposed to the scientific method. This activity is meant to help students design an experiment that is similar to the one we are about to do. The amount and length of these prerequisite lessons depends on your students, the amount of time devoted to science and availability of resources.

Introduction: (Set up may take a while. Give yourself about 20 minutes to be safe.)
Lay out the following materials: spinach leaves, porcelain wide mouth mug, spoon, fingernail polish remover, scissors, coffee filter (already cut to 2" x 8"), toothpicks, ¼ measuring cup, rubbing alcohol, and paper cups. On the board (or students may record in a science journal) in your classroom you will have six categories. Each will be labeled with one of the following abbreviations: O (Observe), K (Know), H (Hypothesize), W (Want to know), L (Learned from experiment), Q (Question further). Ask students what they are thinking. Do not give hints about the experiment. If they need prompting, "think aloud. For example: I know that nail polish remover takes color away. Record these comments under O (Observe) in the chart below.
Review what we have learned about colors. Students should mention that they can be mixed, etc. They should talk about ROY G BIV. Why we see color should also be mentioned. This should be written under the K (Know) in the chart below.
Ask students if there is anything else they would like to know about colors. Jot these down under W (Want to Know).
Explain that we will be investigating spinach leaves to see what colors they have in them. Students should hypothesize what they think will happen as I record on the chart under H (Hypothesize).

Observe, Know, Want to Know, Hypothesize, Learn, Question

We will design our experiment using the LCD and Scientific Method power point. As we go through the slides, we will record information and the criteria needed.

Day 1:
Step 1:
Procedure: (Large group demonstration...if you have access to a document camera, this would be a great tool for students to see what you are doing up close.)
1. Break up the spinach leaves into little pieces and place them into the mug.
2. Using the bottom of the spoon, grind and smoosh the leaves until they become mush. (If you see a lot of liquid, this is great, you will need that.)
3. Add a spoonful of fingernail polish remover to the leaves. (This will help to extract the color.)
4. Continue to grind and smoosh the leaves until you see that the liquid is green from the spinach.
5. Use a toothpick to place a drop of the spinach liquid one inch from the end of the coffee filter. Let it dry.
6. Put ¼ cup of alcohol in the paper cup.
7. Place the end of the coffee filter (with spinach drop) into the alcohol but do not let it touch the alcohol. (The alcohol will travel up the filter paper separating the different colors in the spinach.)
8. Leave for an hour or so. The longer you wait (yes, even over night), the more dramatic your results will be.
9. When you choose to observe the chromatography, note the different colors and explain that the pigments that "got along" with filter paper are the ones at the bottom. The colors near the top didn't, soaked into the filter paper later and that is why they climbed up the paper higher.
Explain that separating colors is known as chromatography. Students should record what they learned on the chart under L (Learn).

10. Discuss questions they have from the results of the experiment. How can we apply this knowledge? What else do students want to know? What other investigations could do based on this experiment? Record this under the Q on the chart.

Day 2:
Step 1: Allow students to review yesterday's OKWHLQ chart and the power point we made (Scientific Method). Tell them that they are the scientists today and they get to design the chromatography experiment themselves. Explain that yesterday's chromatography experiment will help them with today's experiment. Their teacher wants to know what colors create the color black.
Step 2: I will go through the OKWH sections (with the aid of students). I will parallel yesterday's experiment as we decide what we must do with the materials we have in front of us. I will have the following materials lying out: zipper-style sandwich bags, black water-based marker, 2"x10" strips of paper towel, stapler, pipette, and water.
Procedure:
1. Using masking tape or permanent marker, label the bag with the brand name. Use the marker to draw a thin line across one end of the paper towel strip about a ½ inch from the bottom. Staple the top of the sandwich bag to hold the paper strip in place. The other end should touch the bottom of the bag.
2. Using a pipette, drop about ten drops of water into the bottom of the sandwich bag so that the bottom of the paper towel is resting in the water. (It is important that the black line should be above the water level.)
3. Leave for 15 minutes or so. The longer you wait (yes, even over night), the more dramatic your results will be.
Step 2:
Ask the students if all black markers are made up of the same colors or if they are like chocolate chip cookies where there are many recipes. Repeat the procedures above with two different brands of black markers. Be sure to label the bags.
Step 3:
Ask students if they think it will work like mixing colors. Do they think that we will see that yellow and red make up the secondary color orange (green, purple, etc.)? What colors make up the primary colors?
Explain that black is the combination of many colors. Record what they learned on the chart under L (Learn). Discuss questions they have from the results of the experiment. How can we apply this knowledge? What else do students want to know? What other investigations could do based on this experiment? Record this under the Q on the chart.

Teaching Notes and Tips

Spinach Leaves Chromatography: Dr. Heidi Gold-Dworkin states that Red Maple leaves work very well.
Marker Chromatography: Depending on maturity of my students, I may place them into groups follow the same experiment design to test the secondary and primary colors in the marker experiment.
The reason that the marker or dried spinach solution must not touch the liquid the paper is sitting in is because the solution would cause the markers to dissolve into the liquid rather than have the pigment climb the paper.
In the past, the spinach leaves have not worked, the pigment would not travel up the paper. I would do the experiment ahead of time to have a "back up" to replace (just in case).
Chromatography paper works best but coffee filters should work with either experiment. I am not sure if paper towels will work with the spinach experiment and I have yet to try them.
Once, I tried chromatography using the spinach leaf experiment. When it did not work, I consulted a few "senior" science teachers but did not come to a conclusion and I did not investigate further (which really disappointed my students). I also have not attempted to teach students how to lead their own scientific inquiry so I am anxious to see if they can follow my example to create the marker experiment.

Assessment

See the Excel attachment.
Observations during class discussions will also be taken into account.

Standards

Grade 1: Physical Science: Structure of Matter-The student will understand that objects have physical properties: The students will describe objects in terms of color, size, shape, weight, texture, flexibility and attraction to magnets.
Grade 1: History and Nature of Science: Scientific Inquiry- The student will raise questions about the natural world, make careful observations, and seek answers: The student will observe, describe, measure, compare and contrast common objects, using simple tools including but not limited to ruler, thermometer and balance.

References and Resources

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