Last year I came across this leaf chromatography experiment from one of my favourite websites Playdough to Plato. It shows what colours make up a leaf and why they change colour in autumn. Unfortunately all the leaves had long since fallen when I came across it. However I was determined to do it this year. Plus EC and YC ask every year why they do change so this was the perfect experiment to help explain the process.
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You will need:
- Rubbing alcohol
- Cling fling
- Deep sided pan
- Coffee filter paper
For the first part of this you need to go on a walk to find your leaves. EC and YC had great fun filling my bag with all sorts of leaves of every shape and colour.
When you get home begin by tearing up your leaf and put it into a jar/cup. Only one leaf per cup.
Next cover your torn up leaf with a couple of spoonfuls of rubbing alcohol.
Then cover the cup with some cling film. You can either leave this like this over night. As we didn’t want to wait we sped up the process. To do so fill a deep-sided pan with some boiling water and sit the cups in it. Leave this to sit for at least 30 minutes.
While the leaves are “cooking”, cut up your coffee filter into long strips.
After the 30 minutes remove the cling film and take the cups out of the water. The rubbing alcohol should have turned a different colour as it has absorbed the pigment. Finally place the filter paper into the solution; make sure that it doesn’t sink into the solution by hanging some of the paper out of the cup. I asked EC what colours he thought would appear and he said black!
After a few hours (we left ours overnight) you will begin to see different coloured bands appear on the filter paper.
The Science Behind Leaf Chromatography
Leaves had special cells in them called chloroplasts that produce energy and food through the process of photosynthesis. The chloroplasts contain pigments, which is what gives the leaves their colours. Green chlorophyll is the most common type of pigment, but there are also xanthophylls (yellow), cartenoids (yellow/orange) and anthocyanins (red). The green chlorophyll is the most dominant and hides the other colours through most of the year. However, when autumn comes the chlorophyll breaks down allowing the other colours to shine through.
I did this experiment with EC and he was fascinated by it, especially when he saw that one of the bands looked black. He was very happy that his prediction had come true. It was in fact a very deep purple colour, but I didn’t want to spoil his joy and I’m sure he will remember now how the leaves change colour.
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