Weak Bases

[604805638]

Why are weak bases like NH3 not completely ionized? What forces them to not completely dissociate?

[Sandra Maesta 1C]

Hey!
So, it has to do with the equilibrium constants. You see, molecules in a solution are constantly dissociating and reprotonating, and the relative stability of the acid and conjugate base, represented by equilibrium constants, determines the rate of the forward and backward reactions, right? So, equilibrium being a reversible process, the system (the molecules dissociation and reprotonation) is actually a flux. That being said, weaker bases have lower equilibrium constants (considering the forward equation one in which the reactant is the base and the results are the ions OH- and the conjugate bases), which makes their forward reaction less common than the backwards one, which is why there is more reactant (base) than product (dissociated base).

[edward_qiao_3I]

Additionally, weak bases are weak bases because they are more stable and are less likely to take another H to form the conjugate acid, and therefore will result in less production of OH- when combined in an aqueous solution.

[Wayland Leung]

How do you determine just by looking at a molecule that it is a weak base?

[Charles Ang 1E]

How do you determine just by looking at a molecule that it is a weak base?

I'm not quite sure, but I do know that there is chart towards the end of the course reader, right before the sample tests, listing common weak bases.