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The Chemistry of Colour

o Substances are coloured if they absorb energy that is in the visible frequency of the
electromagnetic spectrum.
o The energy absorbed causes electronic changes; electrons are promoted from their ground
state to a higher energy level (they become excited).
o The…

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o These can form part of an extended delocalised electron system called a chromophore.
o Electrons in double bonds are more spread out than those in single bonds, and therefore
require less energy to become excited; this means that the energy absorbed is within the
visible…

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Paints

o Paints contain pigments of different colours mixed with a liquid which carries the pigment
(the medium).
o In water colours, the finely ground pigment is suspended in water; when the water
evaporates it leaves behind the pigment on the page.
o In spray paints,…

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o When restoring historical art work, it is important that the new colours used in retouching are
a good match of the original colours.
o Chemists can identify the colours and select the most appropriate pigments using a variety of
techniques.

Reflectance Spectra

o The surface…

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o Once the reflectance spectrums for the different pigment colours are produced, they can be
used to select another pigment that is the same colour; for example the reflectance
spectrum for a blue-red pigment was measured:




o The reflectance spectrum for ultramarine is as follows:




o…

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Laser Microspectral Analysis (LMA)

o This technique is used to identify the different elements present in a pigment.
o A pulse of high power laser light is focused onto a small sample of paint, resulting in the
vaporisation of the metal compounds (which have high boiling…

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o Glycerol can react with three palmitic acid molecules to form a triester:




o The triesters found in natural oils are usually mixed triesters (the three fatty acid groups are
different:




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Fats and Fatty Acids

o The carboxylic acids in fats and oils are usually unbranched, containing an even number of
carbon atoms ranging from C4 to C24.
o The fatty acids can either be fully saturated (all single bonds) or they can
be unsaturated (contain one…

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o The following diagram shows the structure of an unsaturated triglyceride:




o The unsaturated triglyceride molecules can not pack so closely together due to the kink
caused by the presence of the cis double bonds; the intermolecular forces are therefore
weaker and so less energy is…

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Hydrolysis of Fats

o Like all esters, the ester linkage holding the molecules together can be hydrolysed.
o When this is done with concentrated sodium hydroxide solution, a soap is made.
o Soaps are the sodium or potassium salts of fatty acids and they are made…

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