Thursday 14 November 2013

SCIENCE: Why do leaves change colour in Autumn?

This is a science experiment we tried out today to show why leaves change colour in autumn.  
Leaves changing in autumn is such a magical thing but how does a green leaf change to all some beautiful colours?  

This is an experiment you can do at home to learn how and all you'll need is...

  • Test tubes 
  • Tongs
  • Isopropyl alcohol (surgical spirit will have the same effect)
  • Leaves (green ones) from a deciduous tree (one that looses it's leaves in the winter
  • Leaves (green ones) from a different type of deciduous tree - this is optional but having more than one to compare makes it more fun.
  • Leaves from an evergreen (a tree which leaves remain green all year long
  • Kitchen roll
  • A pan

Now what to do...

Cut the leaves from one of the trees as finely as possible and put it into a test tube labelled A.  Cut the leaves from one of the other trees really finely and put that into test tube B.  Finally cut up the leaves from the last tree really carefully and put into a test tube labelled C.


Fill each test tube with isopropyl alcohol until leaves are completely covered.  Put the lids on firmly.
Heat a pan of water on your stove.

WARNING TAKE LIDS OF BEFORE BOILING (when gases get hot they expand and pressure is increased and your lid will pop off.  We are simply using the lids to avoid breathing in the alcohol unnecessarily and I used them to label what we were doing).

Right, now using your tongs to grab a test tube and hover it in the boiling water (don't let it touch the bottom of the pan if you can help it).


What you are doing is boiling the alcohol - you'll know when it's boiling when the leaves are bouncing about and the alcohol is bubbling - when you look in the test tube you will see that the alcohol has gone green, this is what we want!

Cut three strips of white kitchen roll paper like this...
Dip one strip of kitchen roll into each of the test tubes like this...

We are doing a chromatography test and if you get it right you will be able to see the colours from the green we extracted from the leave split into several colours as it clubs up the paper.

How can we take this further...

Does the progression of colors on the blotting paper follow the same order as the progression of colors that the leaf will actually change?

Does a leaf from one tree e.g an oak, have the same colour pattern on the kitchen roll as from another tree e.g a lime tree?

Does the evergreen have the same colour pattern on the kitchen roll?

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