# Why is boric acid written as B(OH)3 and not H3BO3? [duplicate]

Why is boric acid written as $\ce{B(OH)3}$ and not just $\ce{H3BO3}$, like it should be for an acid?

• I've seen it written both ways. If anything, the second way seems to be more common. – Ivan Neretin Mar 22 '17 at 17:58
• yeah, i did agree in the question, its written both ways, and not just as B(OH)3, but why does this happen only for boric acid? being written in the form of a base @IvanNeretin – Supernova Mar 22 '17 at 18:02
• @QuarkyLittleThing Writing H3PO4 as PO(OH)3 is actually weird. Same applies for H2SO4. For H2SO4 writing it as SO2(OH)2 looks very confusing and rather i would prefer writhing it as H2SO4. I think its just a way of writing. If there is any chemical or structural reason behind that, then I am eager to know. – Yb609 Mar 22 '17 at 18:11

This is mostly because boric acid is commonly believed to have different acidity mechanism. While common acids generally dissociates

$\ce{HNO3 <=> H+ + NO3-}$

boric acid is commonly believed to associate with water

$\ce{H2O + B(OH)3 <=> H+ + [B(OH)4]-}$

this type of acidity is rather common for metal hydroxides, hence the way of writing.

For that matter, not every hydrogen should be written at the beginning of a formula of an acid, but only actually acidic ones. So, $\ce{H2SO4}$, but $\ce{HPH2O2}$

• Even the convention of writing acidic hydrogens at the beginning is not always followed, and it is all too easy to suppose that $\ce{HCOOH + NaOH}$ will give ... $\ce{NaCOOH}$. Oy! – Oscar Lanzi Mar 22 '17 at 19:02
• And given that the second $\mathrm pK_\mathrm a$ of sulfuric acid is a modest $\sim 2$, one could also envision it being written as $\ce{HSO3OH}$. Interestingly, in the early development of chemistry apparently it was thought simply to be an adduct of $\ce{SO3}$ and $\ce{H2O}$! – hBy2Py Mar 23 '17 at 12:40