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peptizing agent is added to convert ppt into colloidal solution. give reason?

Dear student!

The peptizing agent is an electrolyte that gives off ions which are absorbed by the precipitate particles. The similarity in charges leads to the effect of repulsion, causing the precipitate particles to disperse, forming a colloid. For example,when we add a small volume of very dilute hydrochloric acid solution(peptizing agent) to a fresh precipitate of aluminum hydroxide,it leads to formation of an aluminum hydroxide colloid.

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A product that enhances dispersion of a substance (such as clay) into colloidal form. Peptizing agents for drilling-mud clays are sodium carbonate, sodium metaphosphates, sodium polyacrylates, sodium hydroxide and other water-soluble sodium compounds, even common table salt, NaCl, if added at low concentration. The divalent cations on a clay are replaced by the sodium cations, aiding clay hydration and dispersion. Greater benefit is attained by an agent that contributes an anion (for example, carbonate, phosphate or polyacrylate) that precipitates divalent cations and removes them from solution. This process is successful only when the water first contacted is free of hardness ions, otherwise the anion in the peptizing salt (or polymer) will be precipitated by the hard water and make the peptizing agent much less effective.

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