How to determine which is an acid and which is a base?

[Alyssa_Hsu_2K]

Say we were only given NH3(aq), and asked what is its conjugate acids and conjugate base.
I know acids are the proton donors and bases the proton acceptors. However, in this case, how would we know whether NH3 or H2O is the proton donor or acceptor?
Seeing that Oxygen is more electronegative than Nitrogen, why isn't the H from NH3 going to H2O?

[Janette 3B]

In this case you NH3 is a weak base due to the fact that NH3 is not completely ionized in water

[604805638]

Do we just have to memorize the strong bases in order to know that NH3 is a weak base?

[Anna Makridis_L1]

Also NH3 has a lone pair. I think this may be the reason it bonds with the other hydrogen

[Katherine_Zhuo_3B]

Given NH3 (aq), by memorizing the strong/weak acids and bases, we know that NH3 is a weak base. The lone pair on the nitrogen will bond with neighboring hydrogens from the H2O to form conjugate acid NH4+ and conjugate base OH-.

[Logan 3C]

It's really really helpful if you memorize the list in the course reader. Other than that if you think about which one of the two reactants will be more likely to give up a Hydrogen, that is acid. It takes a little bit of thinking ahead for me, but once you consider that it is easier.