0
$\begingroup$

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

$\endgroup$

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

This question appears to be off-topic. The users who voted to close gave this specific reason:

If this question can be reworded to fit the rules in the help center, please edit the question.

  • 1
    $\begingroup$ what are your thoughts/ideas on the question? $\endgroup$ – Apurv May 11 '14 at 14:33
0
$\begingroup$

Wikipedia says boric acid is a Lewis acid. It later states that it is a tribasic Brønsted acid.

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 $\ce{P(OH)3}$.

$\endgroup$
  • $\begingroup$ It also says it's a "tribasic" Bronsted acid. I'm not clear on what that means and it appears there is quite a bit of debate still about its acidity. I just want the best supported answer. $\endgroup$ – Dissenter May 11 '14 at 2:54
  • $\begingroup$ Yes, but what's a tribasic acid? What's a basic acid? $\endgroup$ – Dissenter May 11 '14 at 3:26
  • 1
    $\begingroup$ 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. $\endgroup$ – Jannis Andreska May 14 '14 at 16:51
  • $\begingroup$ Ah, thank you. There are the HS- and S^2- conjugate bases. $\endgroup$ – Dissenter May 15 '14 at 20:33
2
$\begingroup$

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.

$\endgroup$

Not the answer you're looking for? Browse other questions tagged or ask your own question.