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Thread: Colour and UV spectroscopy confusion

  1. #1 Colour and UV spectroscopy confusion 
    Forum Masters Degree organic god's Avatar
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    ok phenolphthalein. in alkaline solution it has a different structure so it appears purple. think the structure isnt that important to this question.
    i know the alternating sequence of single and double bonds gives it colour. but my question is about the colour it takes on.

    phenolphthalein is a purple solution
    The UV spectrum for phenolphthalein gives an absorbtion at 520nm
    so that means that when light of this wavelength is applied. the electrons can absorb the energy etc.
    however it seems to me that ~ 500nm is the wavelength of purple light. so doesnt that mean that this colour will be absorbed.


    Hold on may have answered my own question...
    only absorbs this frequency. electrons increase in energy.
    drop to more stable state and release energy in a photon of the same frequency so we see this colour? not sure if thats right


    everything is mathematical.
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  3. #2  
    Forum Junior Twaaannnggg's Avatar
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    Violet light has a wavelength range of 350 to 420 nm. 520 nm is in the blue-green range and thus there's no contradiction.


    Build a man a fire and he will be warm for a day, set a man on fire and he will be warm for the rest of his life.
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  4. #3  
    Forum Masters Degree organic god's Avatar
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    well although violet may be this wavelength, the colour of the compound is not violet.

    purple is a mix of red and blue, which i reckon would set its wavelength at ~500nm
    everything is mathematical.
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