Saturday, November 19, 2011

Leaf the decorating to the Leaves: Fall Colors

In the fall, the trees turn in their lush green leaves for a more colorful display.  It is always fun to see the variety from red to yellow, and even some unusual colors like purple.    In today’s activity we are going to gather leaves during a nature walk and then do a little chemistry to see what pigment colors really make up that leaf.  Is green the only pigment color in a green leaf or are there more colors that we can’t even see?  This activity takes a lot of parent involvement and was frankly more fun for me than it was for my preschoolers, but they still had a good time. 

Parent Background
Plants have a green pigment called Chlorophyll that captures the light energy from the sun and uses that energy to form sugars.  These sugars are the basis of all of our food supply, because they are the energy source for the plant and all the animals that feed on the plant.  The Chlorophyll is so abundant in leaves that most leaves look completely green all summer.  In the fall when the temperatures start to cool, the days grow shorter and the light from the sun is less direct trees and other plants begin to shut down their sugar making factory and the leaves no longer make chlorophyll.  As the leaf starts to die and the chlorophyll fades we get to see some of the other pigments naturally in the leaves.  These pigments were always there in small amounts and helped the tree to absorb other wavelengths of light not used by the chlorophyll.  However, because they are only present on a small scale they are only visible once the plentiful green pigment is no longer present.  Today’s experiment uses rubbing alcohol as a carrier to separate the leaf pigments on a piece of filter paper so that colors other than those visible in the leaf can be seen.  This works because the rubbing alcohol dissolves the pigments and carries it with them up the paper, the alcohol evaporates leaving the pigment behind.  Each pigment forms its own line because different colors have different weights and are carried different distances before the alcohol dissolves. 

Our Leaves:  Red, Purple, Yellow, Green
Mason Jars or other Glass Jars or Bowls with a lid (one for each color of leaves)
Clothes pins, tape, or paper clips to clip coffee filters to jar
Colored Leaves from a Leaf Walk (Try to get ones right from the tree or that are still moist and don’t forget green leaves as well as the fall color leaves)
Rubbing Alcohol to fill each jar about 1.5-2 inches

Ground Up Leaves
Coffee Filters – cut into 2 inch stips (one strip per jar)

Small food processor, blender, grinder, or hand chopper

Cake pan to use as a hot water bath.

Procedure:  Do this experiment in a well-ventilated area.

1.        Take your children out to pick fall leaves.  Try to get at least 3 colors making sure to include green.  You will need a handful of each color. 

2.       Have your children separate leaves into jars with like colors so each jar only holds one color.

3.       Determine how much rubbing alcohol is required to fill your jar to the 1.5-2” mark.

4.       Making sure to protect your eyes while grinding the leaves in alcohol.  Place leaves and rubbing alcohol in your food processor, other appliance or grind them by hand making sure to produce small pieces so that the rubbing alcohol can dissolve the pigment from the cells. 

5.       Pour each alcohol/leaf mixture into a jar and rinse the bowl before doing the other color.

6.       You will notice the alcohol starting to take on each leaf color and should ask your children what color the leaves and alcohol is in each bowl.

7.       Once each bowl or jar is filled with a leaf mixture, loosely cap, and place it in a hot water bath (just around the bottom) for 30 minutes to allow the alcohol to pull as much pigment as possible out of the leaves, turning black is a great sign but mine didn’t quite get there and still worked great.  I poured boiling water into a glass cake pan around the jars.

8.       Cut Coffee filters into 2 “ strips and write the name of each leaf color on the strip. 

9.       Uncap the jars and lip or tape the strip to the rim of the jar with the bottom of the strip in the leaf/alcohol mixture.

10.   Wait one hour or more to allow the alcohol to be absorbed and evaporated from the coffee filter strips.  Ask your kids to see what colors they can find.  Our results are below:

Red Leaves:  Red and yellow sections of color.  Green Leaves:  Yellow Lines, Green Lines
 Yellow Leaves:  Yellow Line, Green Line.  Purple Leaves:  Purple color throughout, green line, yellow line.

Check back for a classic toddler leaf activity on Tuesday.  Until then – Happy Thanksgiving.

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