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The p-Block Elements
Boric Acid
1 question from 1 paper, each with its answer.
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Concepts tested
- Boric acid as a Lewis acid
All Questions
2003 AIPMT 1 question
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Which one of the following compounds is not a protonic acid :A protonic (Brønsted) acid releases a proton ($H^+$) from its own –OH group.
$PO(OH)_3$ (phosphoric acid), $SO(OH)_2$ (sulphurous acid) and $SO_2(OH)_2$ (sulphuric acid) all ionise by releasing $H^+$ from their –OH groups.
Boric acid, $B(OH)_3$, does not release its own proton. Boron has an incomplete octet, so it accepts an $OH^-$ ion from water, which releases $H^+$ from the water:
$B(OH)_3 + H_2O \rightarrow [B(OH)_4]^- + H^+$
So boric acid is a weak monobasic Lewis acid, not a protonic acid.
So the compound that is not a protonic acid is $B(OH)_3$.