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Unformatted text preview: ls in that much larger amounts of electrolytes are requ ired to bring ab out precipitation.
T h e r e a s o n i s t h a t l y o p h i l i c particles are to some extent protected by a layer of
bound water molecules, e.g. a protein such as gelatin, which can be regarded as
surrounded by a film of water through which ions cannot easily penetrate.
Higher concentrations of electrolytes do, however, exert a salting-out effect,
this results from the tendency of the ions to bind water molecules which are
thus less available to the substance being precipitated.
The high sensitivity of lyophobic particles to precipitation by electrolytes can
sometimes be reduced by the addition of a lyophobic substance, which is said to
be a protective colloid and to exert a protective action, the protective substance
becomes adsorbed on the surface of the lyophobic particles and protects them from 4 the approach of ions of opposite sign.
A lyophilic sol can be coagulated and yield a semi rigid jelly-like mass that includes
the whole of the liquid present in the sol. The product is known as a gel.
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