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 different colors are made.
- Students will design an extension activity using spinach leaves based on this experiment.

Context for Use

This lab activity is appropriate for a primary classroom with appx. 20-25 students. I would allow two 45-60 minutes sessions for this activity because I will be walking students through the scientific process as I teach them. For optimal results, you should allow 24 hours for each experiment to take place and have students exposed to the scientific method frequently. You will need 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.
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 already did. This activity might be a bit over the heads of beginning first graders but can easily be adapter to older grades.

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

Description and Teaching Materials

I would introduce this unit using the 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 already did. This activity might be a bit over the heads of beginning first graders but can easily be adapter to older grades.
Introduction:
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. Ask students what they are thinking. Record 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

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:
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 soak into the filter paper as well 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).

Day 2:
Step 1: Allow students to review yesterday's OKWHL 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 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:
Tell students that you wonder if all black markers are made up of the same colors or if they are like chocolate chips (there are many recipes). Repeat the procedures above with two different bands 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).

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 did not investigate further. 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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