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Question
A colloidal sol is prepared by the given method in the figure. What is the charge on hydrated ferric oxide colloidal particles formed in the test tube? How is the sol represented?
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Solution
Colloidal particles usually adsorb those ions which are in excess and are common to its own lattice. This preferential adsorption of a particular type of ions imparts a particular type of charge to colloidal particles.
When FeCl3 is added in NaOH, the constituent of the sol is Fe(OH)3 but the dispersion medium is having an excess of OH- ions. Hence, it gets preferentially adsorbed to the sol giving the overall negative charge. The sol is represented as Fe2O3.xH2O / OH-
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