‘Philic’ means loving and ‘phobic’ means hating.
Lyophilic colloids are therefore, colloidal solutions in which dispersed phase has great affinity for dispersion medium. These solutions are quite stable and are reversible in nature. Eg. sols of gum, gelatine, starch, proteins and certain polymers in organic solvents.
Similarly, lyophobic colloids are colloidal solutions in which dispersed phase has very little affinity for the dispersion medium.
Such solutions are unstable and are irreversible in nature. Eg. Sols of metals and their insoluble compounds like sulphides and oxides.
Lyophobic colloids can be easily coagulated because on addition of small amount of electrolyte, the charge on colloidal particles is removed, due to which the particles will come closer to each other and under the influence of gravity, they combine to form a cluster and settle down.
(i) A process known as electrophoresis occurs.
When electric current is passed through a solution, then positively charged ions move towards cathode and negatively charged ions move towards anode and then they get coagulated.
(ii) A process known as Tyndall effect occurs.
When a beam of light is passed through a solution, the light gets scattered by the colloidal particles and path of light becomes visible.
(iii) Coagulation occurs.
We know that lyophobic colloids can be easily coagulated because on addition of small amount of electrolyte.
When NaCl is added to ferric hydroxide sol, a negatively charged solution is obtained with absorption of OH– ion as the positively charged colloidal particles of ferric hydroxide sol get coagulated by the oppositely charged Cl− ions provided by NaCl.
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