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9) Biphasic titration
This is done in case of salts which are water soluble but their
corresponding acids are not, e.g. the assay of sodium salicylate or sodium
benzoate. The salt solution in water is titrated with HCl in the presence of
methyl red indicator and ether (immiscible solvent). Salicylic (or benzoic)
acid is liberated and is soluble in ether. At the end point only NaCl is
present in aqueous layer and the first drop in excess of the titrant
produces a color change of the indicator.
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