Kaplan FL#8 PS Q#1

[170559]

How many hydrogen bonds does boric acid(H3BO3) form? Kaplan's answer says 9, 3 with the positively charged hydrogens and 6 with the lone pair's on oxygen. Can both the lone pair really form hydrogen bonds? In that case does water form 4 hydrogen bonds? Should I be thinking about steric hindrance in this case? I am fully confused!

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[TieuBachHo]

I think you are right. By looking at the three dimentional structures of water and boric acids, they form almost the same way with tetrahedral 109.5 degree. So the hindrance here is limited as compared to the available lone pairs of Oxygen. I actually think it's less hindered than the H2O bonds due to the spacial nature given by Boron molecules. If I am not wrong then H2O form 4 H bonds.