To demonstrate the separation of pigments in plants through the process of chromatography
Small clear jar (baby food jar)
Leaves (green and red)
Cut the filter paper into 1" x 1.5" strips (depending on jar size) and tape to the middle of the pencil. When the pencil is balanced across the top of the jar, the paper should hang freely, not touching the bottom of the jar. This saves a lot of time.
1. Assign half of the class green leaves and the other half red leaves.
2. Distribute materials.
3. Place the leaf upside down (so that the bottom of the leaf is up) on the filter paper relatively close to the bottom of the strip and rub gently on the leaf with the pencil lead. Make the rubbing approximately the size of a nickel.
4. Readjust the leaf and continue rubbing until the spot on the filter paper is dark green or red, depending on the leaf assigned.
5. When rubbing is completed, balance the pencil with filter paper in the jar.
6. Fill the jar with rubbing alcohol until the liquid just touches the bottom of the filter paper.
Teacher Note: I suggest that the teachers distribute the alcohol.
Safety: Inform the students not to put their noses in the jar to smell the alcohol. Explain the "rule of wafting": take a deep breath and then waft the scent towards your nose to smell.
7. Let the experiment stand for 15-30 minutes.
8. Observe the filter paper and record observations.
The alcohol has moved up the paper and the pigment has moved from its original location. New pigments are now present on the filter paper and staggered location along the paper.
As the alcohol moves up the paper, the pigment dissolves into it. Because of the different characteristics of the pigments in the leaf, some pigments move faster than others.
Teacher note: Because of the different chemical properties of pigment molecules, pigments will move at different rates.
During the spring and summer, the red and yellow pigments in these maple leaves are masked or hidden by large amounts of chlorophyll in the leaf. This is not unlike making a batch of chocolate chip cookies. If we added ten pounds of flour, five chocolate chips, and a pinch of sugar, what would we taste? Flour. Similarly, we only see the chlorophyll because there is such a large amount. So why are the other leaves read? Because they have already changed for the season. In fall, chlorophyll breaks down and reveal the wide range of colors produced by these other pigments. This occurs because during the fall, the tree is forming a plug at the base of the stem, which cuts off the water to the leaf. Because there isn't any water, the leaf stops making food, chlorophyll breaks down, and we start to see the other colors.
Kelley Bassett, 2000.