In a process called ‘chromatography’, scientists can separate the individual parts of a mixture so that each one can be identified separately. In the following science experiment, use ‘chromatography’ to analyse which other ‘pigments’ are present in green leafs, to try and predict what colour the leaves will turn in the fall:
Topics covered
Pigment, Chromatography, Capillary action
What will I need?
GREEN TREE LEAVES
COFFEE FILTERS
SCISSORS
3x SMALL GLASS JARS
3x PENCILS
RUBBING ALCOHOL
RULER
Procedure (Method)
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How does it work?
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In this science experiment you can predict the colour that green leaves will turn in the fall by separating all the colour pigments contained in a green leaf, in a process called ‘chromatography’. During ‘chromatography’, the rubbing alcohol (solvent) moves up the paper by capillary action, this occurs as a result of the attraction of the alcohol molecules to the paper. As the alcohol rises through the paper, it meets and dissolves the pigment, which will then travel up the paper with the alcohol solute sample. Different compounds in the sample mixture (the pigment) travel at different rates due to competition between the paper fibres and water for the solutes.
The pigments found in leaves are used in a plant’s food making process, called ‘photosynthesis’. Different colour pigments absorb different wavelengths of light to make this process more efficient for the plant. The main pigments are ‘Chlorophyll A’ and ‘Chlorophyll B’, which causes the green colour of a leaf. Other pigments you may see are: yellow pigments (xanthophylls – Birch & Ash trees), orange pigments (carotenes – Maple trees) or Brown / Red pigment (anthocyanins – White oaks).
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