5. what are lyophilic and lyophobic sols? Give one example of each . Why hydrophobic sols are easily coagulated ?
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Hydrophobic sol or lyophobic sol get discharged when they meet electrolyte of opposite charge.....due to which they get coagulated
Answer:
(i) Lyophilic sols: Lyophilic sols are colloidal sols that are formed by mixing substances such as gum, gelatin, starch, etc. with a suitable liquid (dispersion medium). These sols are reversible in nature i.e., if two constituents of a sol are separated by any process, such as evaporation, then the sol can be prepared again simply by shaking the mixture of dispersion medium and dispersion phase.
(ii) Lyophobic sols: Colloidal sols are not formed, when substances such as metals and their sulphides are mixed with the dispersion medium. Only special methods are used to prepare their colloidal sols. Such sols are called lyophobic sols. These sols are irreversible in nature. For example: sols of metals.
Now, two things determine the stability of hydrophilic sols – the salvation of a colloidal particle and the presence of a gas.
At the same time, the presence of a charge determines the stability of a hydrophobic sol. Therefore, the former is much more stable than the latter. If the charge of hydrophobic sols is removed (by addition of electrolytes), then the particles present in them come closer and form aggregates, leading to precipitation.