This is the most important rule to know for acid-base reactions:
Stronger acid plus stronger base gives weaker acid plus weaker base.
The relative strengths of the starting acid and the final acid (i.e. the “conjugate acid”) give you a rough idea of how favored it should be.
How do you tell if an acid is stronger or not? Well, to be honest it really helps to have a pKa table. Some instructors say, “don’t memorize pKas”, but I think it’s essential to have this list in your head – at least these 10 rough values. You wouldn’t want to play poker without knowing the value of the hands, right? You’ll find this useful all through Org 1 and Org 2.
HCl: –8 (stongest acid on this list)
H2SO4: -3
H3O(+): –2
Acetic acid: about 5
NH4(+): 10
Water, alcohols: about 16-18
Acetylene: 25
H2: about 35 35
NH3: 38
Alkanes: 50 (weakest acid on this list)
Here’s a quick example.
Tomorrow: how acidity and basicity are related.
Thanks for reading! James
P.S. For a more detailed walkthrough, see this post: “How to Use a pKa table“