Mechanism of Acidity - Boric Acid [closed]

How does boric acid behave as an acid? Is it a Lewis acid or a Brønsted-Lowry acid?

closed as off-topic by Klaus-Dieter Warzecha, tschoppi, user2117, Philipp, MichielMay 11 '14 at 20:10

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• what are your thoughts/ideas on the question? – Apurv May 11 '14 at 14:33

A Brønsted acid is a compound that is able to provide $\ce{H^+}$ ions. A Lewis acid is a compound that can accept an electron pair; it would need to be electron poor. Some molecules have both characteristics and either feature could be used in explaining the reactivity of the compound.
Tribasic means that there are 3 hydrogens that can be used. I'm believe that the author used the term basic acid to mean that the hydrogen is attached as a hydroxyl group instead of hydrogen bonded. Phosphorous acid is always written as $\ce{H3PO3}$, although it could be written as $\ce{P(OH)3}$.
• The term "basicity" of an acid refers in this context to the number of conjugate bases. $\ce{H3BO3}$, when reacting as a Brönsted acid, is tribasic because the 3 conjugate bases $\ce{H2BO3^-}$, $\ce{HBO3^{2-}}$ and $\ce{BO3^{3-}}$ are formed in the dissociation steps. The term does not imply that the acidic protons are bound to an oxygen (OH group). $\ce{H2S}$, for example, can be described as a weak dibasic Brönsted acid. – Jannis Andreska May 14 '14 at 16:51
Boric acid is a Lewis acid, therefore when in water it accepts the lone pair from oxygen and becomes $\ce{(OH)3B^{-}-OH2^{+}}$. From this compound a proton can be donated and this is how boric acid behaves as a Brønsted acid.