Why is it that all strong bases contain at least one hydroxide bond? What is going on here at the chemical level? For example, we know that $\ce{NaOH}$ is a strong base. I know it is strong because it completely dissociates in water. And under the Bronsted-Lowry definition of bases, I know that is is considered a base because it accepts a proton. So what is it about having a hydroxide bond specifically that lets it dissociate?
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$\begingroup$ Not clear what you are asking here. NH3 is a base, but doesn't have any hydroxide, Fe(OH)3 has plenty of hydroxide but is not basic. $\endgroup$– Burak UlgutCommented May 2, 2018 at 17:51
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$\begingroup$ NH3 is a weak base though. I am specifically talking about all strong bases. And I don't mean to say that all compounds with hydroxide bonds are strong bases, just the other way around. (Or at least the vast majority of strong bases) $\endgroup$– EliCommented May 2, 2018 at 17:55
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3$\begingroup$ There’s no hard and fast rule that a strong base should have a -OH group. Refer Which is the strongest base? $\endgroup$– MollyCooLCommented May 2, 2018 at 18:02
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3$\begingroup$ Sodium hydride and sodamide are strong bases with no hydroxide bond present $\endgroup$– WaylanderCommented May 2, 2018 at 18:32
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$\begingroup$ There is not such thing as a "hydroxide bond" afaik. $\endgroup$– Buck Thorn ♦Commented Oct 22, 2022 at 9:23
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2 Answers
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All strong bases you know contain at least one hydroxyl group because we live in a world dominated by water, almost like in that old movie with Kevin Costner. Water chemistry is of paramount importance to us, and acid/base reactions in water pretty often boil down to $\ce{H+ + OH- ->H2O}$.
There is nothing special about the hydroxyl group that lets it dissociate. Come to think of it, the group itself does not even dissociate in bases - I mean, $\ce{O}$ and $\ce{H}$ remain together, the bond between them does not break. (It does in acids, but that's another story.) If you mean the dissociation of metal hydroxides, there is nothing special here either. $\ce{NaOH}$ dissociates like any water-soluble ionic compound. On the other hand, $\ce{Fe(OH)3}$ refuses to dissociate, like any water-insoluble ionic compound, of which there are plenty.
In a wider chemical world outside, there are bases which are many orders of magnitude stronger than that, and they don't contain any hydroxyl groups whatsoever. $\ce{NaNH2}$, $\ce{NaH}$, $\ce{BuLi}$ come to mind. You don't see them much in everyday life, though, because they don't survive in our world. Water act as an acid on them, and instantly transforms them to mere $\ce{NaOH}$, etc.
So it goes.
answered May 2, 2018 at 19:04
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Not all strong bases are hydroxides. Guanidine has no oxygen at all and is not ionic in its free base form, yet it competes with alkalies. The highly stabilized, delocalized electron structure of the cation formed upon protonation gets credit in one of the strongest non-ionic bases.
answered May 3, 2018 at 0:00