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I know pH of a solution increases with increase concentration of $\ce{OH-}$.

I'm wondering: when adding MEA, is the $\ce{OH-}$ group from the MEA breaking off, or is it the whole MEA molecule taking a hydrogen from $\ce{H2O}$ leaving the $\ce{OH-}$?

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  • $\begingroup$ Nitrogenous bases work as Brønsted bases because the nitrogen can pull a proton from water to produce hydroxide. $\endgroup$ – Zhe Mar 18 at 16:32
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It is the latter case where "the whole MEA molecule is taking a hydrogen from $\ce{H2O}$ leaving the $\ce{OH-}$". Alcohols very seldom acty as arrhenius bases adding $\ce{OH-}$ to solution. One exception is triphenylmethanol but I cannot think of a second that isn't a variation of the given example. Instead the unbonded electron pair of the amine will abstract a hydrogen from water to form an ammonium ion leaving a hydroxide counter ion and thus raising the pH.

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