4 Extracting colors from leaves (leaf chromatography)
Cost: Less than 6.00 Difficulty: Low Time: Low (hour) Continuous: No, but can be.
Summary:
Chromatography is the separation of a mixture by passing it through a solution. Students will extract the pigments (colors) out of leaves. Leaves contain different pigments, which give them their color. Green chlorophyll is the most common type of pigment, but there are also carotenoids (yellow, orange) and anthocyanin (red). Chlorophyll, which is essential for photosynthesis, usually hides the other pigments, except when autumn comes along and it begins to break down. This is why leaves turn different colors in the fall. Do this project to see some of the hidden colors in a green leaf and predict what color it will be in the fall!
Pro-tip: Rubbing alcohol can be poisonous if consumed, and is toxic if inhaled, adult supervision is recommended.
ELO’s – chemistry, solutions, dissolving, solute, solvent, chemistry, molecules, life science, plants, observation, discussion, building a hypothesis, critical thinking. Why leaves change color?
Supplies needed:
· A few green leaves from 3 different kinds of trees (trees with a dramatic color change like maples, work best during Fall). If possible get two of eat so students can see what the leaf looked like prior as well as the results of the same leaf torn up.
· 3 small drinking glasses (or clear containers)
· Rubbing alcohol
· Plastic wrap
· A pan or tall glass of hot tap water (microwave)
· Coffee filters (to make strips to absorb the color)
· Scissors
· Tape
· 3 pencils
Activity:
1) Keep leaves from different trees separate and follow the steps below for each set of leaves, so you can compare results later.
2) Tear the leaves into small pieces and then put the pieces of each leaf into different glasses.
3) Have an adult pour rubbing alcohol into each glass so that all the leaf pieces are covered. Put a piece of plastic wrap over the top of each glass to keep the alcohol from evaporating (getting soaked up by the air).
4) Let an adult set the glasses in the pan of hot water and leave them for about 30 minutes. Check to make sure the alcohol in each glass has turned green before you take them out. If it hasn’t, refill the pan with hot water and put the glasses back in until the alcohol turns green.
5) While waiting during step 4, cut your coffee filter into strips. Tap a strip to the middle of a pencil so you can hang into glass. Make sure strips are long enough. Make at least one strip for each glass.
6) Once the alcohol in each glass has turned green, take the glasses out of the hot water. Set a pencil with the paper strip taped to it over each glass so that the paper strip hangs down and the end touches the alcohol in the glass. Make sure the coffee filter paper is long enough to reach the rubbing alcohol in the glass, but not too long. Trim if necessary.
7) Let the glasses and papers sit for about 30 more minutes and then check to see if anything is happening. You should see the green color start to soak up on the Wait even longer to see if any other colors appear on the paper strips. Have the duplicate leaves next to each filter paper as shown in the example picture for comparison.
Discussion:
This is a good opportunity for students to write down what they observed and then discuss.
The alcohol and the heat from the hot water made the color in the leaves dissolve so you could see it in the alcohol. Think of what happens when you make tea. When you put a tea bag (filled with tea leaves) in a cup of hot water for a few minutes, the water becomes colored and flavored by the tea leaves. When you put the paper strips into the green-colored alcohol, the colors will be soaked up by the paper allowing you to see a couple different shades of green.
If you waited long enough, you might have been able to see other colors from the leaves appear on the paper – such as orange or yellow. If you saw colors besides green, those are the colors that the leaves will change into in the fall. Were there any differences in the colors from the different kinds of leaves you tested? The reason you couldn’t see all those colors in the green leaves or in the alcohol solution is because the chemical that causes the green color is much stronger than the chemical that causes orange, red, and yellow.
When you put the paper into the alcohol solution, the colors had a chance to separate, and the orange or yellow are were no longer covered up by the green pigment. The same thing happens when leaves start to change colors – the chemical that makes them green starts to decrease with the chemicals that make other colors remain. This is why leaves become pretty colors in the fall!