How to See a Rainbow in a Leaf – Chromatography for Kids
Oct 07 2014
What colour are leaves?
Easy! Leaves are green, except in autumn when many leaves turn red, yellow and brown.
But did you know that there is actually a whole rainbow of colours inside every leaf, all year long?
This rainbow is created by the different chemical compounds found in leaves. The main compound is chlorophyll, which is necessary for photosynthesis - the chemical process that uses sunlight to turn carbon dioxide and water into nutrients to help the plant grow.
Chlorophyll also gives leaves their trademark hue because it is naturally bright green - all the better for absorbing as much light as possible. However, chlorophyll only absorbs red and blue coloured light, so leaves contain pigments (like yellow and orange) to capture other colours of light. It’s possible to see all these pigments at once by performing a fun, child-friendly science experiment!
You can reveal the myriad colours in a leaf through a simple process called chromatography. This process separates all the chemicals present in an object, allowing you to identify each one.
Using Chromatography to See a Rainbow in Leaves
You will need a few materials for this experiment:
- Coffee filters
- Rubbing alcohol
- Glass jar
- Tin foil
Step 1: Cut the coffee filter into one inch strips. Cut one end of each strip into a point.
Step 2: Place a leaf onto the paper, about ¼ of an inch above the pointed end. Take a coin and roll it over the leaf, pressing the green ‘juices’ into the paper.
Step 3: When the paper is dry, repeat the process with 3 more (different) leaves.
Step 4: Fill a jar with a small amount (1/2 inch layer) of alcohol.
Step 5: Tape the paper strips to a pencil, and balance the pencil across the jar so just the very tip of the strip touches the alcohol. The leaf juices should not touch the alcohol.
Step 6: Lay a piece of foil over the jar to prevent the alcohol from evaporating.
Step 7: Watch as the alcohol moves up the filter paper, carrying the colours along with it. In 10-20 minutes the colours will have separated and you will have your very own chromatograph!
You’ll probably recognise the colours that show up on the strip – they are the vibrant and beautiful colours that you see when the leaves change in autumn. Like the green colour of chlorophyll, they’re also caused by different pigments. A compound called anthocyanin gives a shade of red, while different carotenoids produce yellows and browns.
In spring and summer, there is more chlorophyll than anything else, so the result you see is a green leaf. As the amount of sunlight decreases in autumn, there is less light for chlorophyll to absorb and the amount of chlorophyll in the leaf decreases. However, other compounds like carotenoids and anthocyanins increase to absorb light more effectively. That’s why leaves change colours.
You don’t have to wait all year to witness this rainbow of colours! It’s always hidden in the leaf – as this little test reveals.
Hungry for more?
If you are interested in chromatography, you may enjoy this recent interview with Wolfgang Lindner. Lindner was a Jubilee Medal winner in 1991 and was awarded the Society’s Martin Medal in 2009. In fact, he was the first person to have been awarded both medals. In this interview, he reflects on his distinguished career and also muses on the current status of separation science – an amazing opportunity to get an insider’s glimpse at this fascinating scientific field.
Image Source: Rainbow Leaf
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