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Orthoboric Acid MCQ - Practice Questions with Answers

Edited By admin | Updated on Sep 25, 2023 25:24 PM | #NEET

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Boric acid is polymeric due to 

Boric acid is an acid because its molecule:

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Orthoboric Acid

Orthoboric acid, H3BO3 is a white crystalline solid, with soapy touch. It is sparingly soluble in water but highly soluble in hot water. It can be prepared by acidifying an aqueous solution of borax.

\mathrm{Na_{2}B_{4}O_{7}\: +\: 2HCl\: +\: 5H_{2}O\: \rightarrow 2NaCl\: +\: 4B(OH)_{3}}

It is also formed by the hydrolysis (reaction with water or dilute acid) of most boron compounds (halides, hydrides, etc.). It has a layer structure in which planar BO3 units are joined by hydrogen bonds as shown in the figure given below. 
Boric acid is a weak monobasic acid. It is not a protonic acid but acts as a Lewis acid by accepting electrons from a hydroxyl ion:

\mathrm{BOH_{3}\: +\: 2HOH\: \rightarrow \: [B(OH)]^{-}\: +\: H_{3}O^{+}}

On heating, orthoboric acid above 370K forms metaboric acid, \mathrm{HBO_2} which on further heating yields boric oxide, \mathrm{B_2O_3}.

\mathrm{H_{3}BO_{3}\: \overset{\Delta }{\rightarrow}\: HBO_{2}\: \overset{\Delta }{\rightarrow}\: B_{2}O_{3}}

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