1.

Compound (A) on reaction with iodine in the solvent diglyme gives a hydride (B) and hydrogen gas. The product (B) is instantly hydrolysed by water or aqueous alkali forming compound ( C) and liberating hydrogen gas. The compound ( C) in aqueous solution behaves as a week mono basic acid. But in presence of certain organic polyhydroxy compound behaves as a strong monobasic acid. The hydride (B) in air catches fire spontaneously forming oxide which gives coloured beads with transition metal compounds. Aqueous solution of product (C) can be titrated against sodium hydroxide using phenolphthalein indicator only in presence of:

Answer»

`cis-1,2 DIOL`
trans-`1,2` diol
borax
`Na_(2)HPO_(4)`

SOLUTION :If certain organic polyhydroxy compounds such as glycerol, manitol or sugars are added to the titration mixture, then `B(OH)_(3)` behaves as a strong monobasic acid and it can be now titrated with `NaOH` and the end point is detected using phenolphthalein as indicator `(pH=8.3-10.0)`.
The added compound must be a cis-diol, to enhance the acid properties. The cis-diol forms very stable complex with the `[B(OH)_(4)]^(-)` thus removing it from solution.The REACTION is reversible and thus removal of one of the products shifts the equilibrium in the forward direction and thus all the `B(OH)_(3)` reacts with `NaOH` in effect it acts as a strong acid in the presence of the cis-diol.
`B(OH)_(3)+NaOH to Na[B(OH)_(4)]+NaBO_(2)+2H_(2)O`

Reactions involved
`(A)2Na[BH_(4)](A)+I_(2)underset("solution")overset("in diglyme")to B_(2)H_(6) , (B)+H_(2)+2NaI`
`B_(2)H_(6)+6H_(2)Oto2H_(3)BO_(3)( C)+3H_(2)`
`B(OH)_(3)+2H_(2)O hArrH_(3)O^(+) + [B(OH)_(4)]^(-) , pK=9.25`

`B_(2)H_(6)(B)+3O_(2)toB_(2)O_(3)+3H_(2)O`
`COO + B_(2)O_(3)to Co(BO_(2))_(2)`(cobalt metaborate -BLUE colour bead).


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