Identifying Bronsted Acid and Base

[Jenny Chau 1I]

I feel like I'm thinking about this too hard but how would you be able to identify a Bronsted acid and base if there isn't a reaction? For example, problem J1 asks to identify whether NH3, HBr, etc are acids or bases.

[Chem_Mod]

In the Bronsted defenition, an acid is a proton (H⁺) donor, and a base is a proton acceptor. Therefore, it can be determined by the formula whether there is the ability for a proton acception/donation. Drawing the Lewis structure for the given molecules may make this more clear!

[Brittney Nguyen 2L]

For problems like that, I like to consider the compound's potential to form a coordinate covalent bond with a proton (in which case the compound would be a base) or the compound's potential to lose a proton (making the compound an acid) based on formal charge.

For example, NH3 has a lone pair. That lone pair can be used to form a coordinate covalent bond with a proton, since H+ has no electrons. This means that NH3 is a base. NH4+, however, is an acid. This is because atoms like to have a formal charge of 0, but the N in NH4+ has a formal charge of +1. Losing a proton would give N a formal charge of 0.

Like Dr. Lavelle said, Lewis structures really help!