How do I decide if an acid or base is a Brønsted-Lowry or Arrhenius?

Question

Do I need to make some sort of equation? I understand the rules (for Arrhenius acids are H and bases are OH-. But how do I come to the conclusion that a compound has these. Or how do I know that a Bronsted-Lowry donates a proton on a certain acid or base. Please use simple terms as I don't understand chemistry at all. Thank you!

Answer 1

No calculations are typically required for deciding if an acid or base is B-L or Arrhenius.  Like you said, Arrhenius acids have H+'s to donate, and Arrhenius bases have OH-'s to donate.  It's extremely similar to the B-L definitions, which states that an acid can donate H+ (also referred to as a "proton") and a base can accept H+.  Here's the thing that you have to know: all Arrhenius acids are B-L acids (same with bases), but not all B-L acids/bases are Arrhenius acids/bases.  Other than that, it takes looking at a provided reaction or simply being familiar with how chemicals behave.  

Examples:

HCl will break up into H+ and Cl- , which means that it donates an H+, making it both an Arrhenius acid and a B-L acid.

NaOH breaks up into Na+ and OH-, which makes it an Arrhenius base.  Also, the OH- can accept an H+ to make water, H2O, which makes it a B-L base as well.

NH3 can accept an H+ and become NH4+ , making it a B-L base.  However, there is no OH- in its chemical formula for it to donate, so it is not an Arrhenius base.  How do I know that NH3 becomes NH4+ and not NH2- ?  Honestly, things like that come down to familiarity with chemistry (there's a reason in its structure and electron distribution, but that gets pretty technical, so I'll spare you).