Boric acid can be titrated against sodium hydroxide using methyl orange as indicator only in thepresence of polyhydroxy compound like catechol, mannitol, etc. Explain .

Boric acid can be titrated against sodium hydroxide using methyl orang

1.	Boric acid can be titrated against sodium hydroxide using methyl orange as indicator only in thepresence of polyhydroxy compound like catechol, mannitol, etc. Explain .
Answer» Solution :`B(OH)_(3)` reacts with `NaOH`to formsodium METABORATE. `B(OH)_(3) + NaOH rarr Na^(+) BO_(2)^(-) + 2H_(2)O` The end pointduringthe titrationof `H_(3)BO_(3)` with `NaOH`is not SHARP since `NaBO_(2)` undergoesexcessive HYDROLYSIS to give back `H_(3)BO_(3)` and `NaOH` `NaBO_(2) + 2H_(2)O hArr B(OH)_(3) + NaOH` HOWEVER,when certainpolyhydroxycompounds such as catechol, glycerol, mannitol or sugarsor any other cis-1,2,3is added totitration solution, the metaborate ION combaines withpolyhydroxy compound toform a complex. Due to formation of this complex, `BO_(2)^(-)` ion does not undergo hydrolysis. As a result, boric acid betweenas a strongmonobasicacid and the end point can thus be easily detected.