identifying polyprotic acids and bases [ENDORSED]

[Tyler Thompson 1A]

How do you identify a polyprotic acid or base?

[Taylor Aguinaldo 2B]

Polyprotic acids have two or more protons that can be donated to other compounds. On the other hand, polyprotic bases can accept at least one H+ ion, or proton, in acid-base reactions. This can be remembered as "poly" means mulitple and "protic" simply refers to protons.
Some polyprotic acid examples: H2SO4 (which is emphasized in our syllabus), H3PO4
Some polyprotic base examples: SO4^2-, PO4^3-

[Chem_Mod]

Poly = many, protic = hydrogen with +1 charge

I'd say some of this is just memorization of the polyprotic compounds Dr. Lavelle mentioned in lecture. But in general,
if you see a compound that has at least 2 Hydrogens in the front, it has multiple protons it can donate (example H2SO4). Whereas, HCl only has 1 H+ to donate, meaning it could not be a polyprotic acid.

For polyprotic bases, a negative 2 charge or lowerr (meaning -3,-4, etc) would be an indicator that it can most likely accept more than 1 H+. For example, SO4 2- can accept 1 H+ to be HSO4-. And this ion already has a H+, but still a negative charge, so we can think maybe it can accept another positively charged proton to become nuetral (H2SO4). So you can also think of it as, can its fully dissociated base accept more than 1 proton?

Using the HCl example, Cl- (fully dissociated conjugate base) would become HCl, which has a neutral charge already with one proton. And in this case, our conjugate base (Cl-) didn't have a charge -2 or lower, so it makes sense that it is not a polyprotic base.

Another giveaway would be if they give you multiple Ka or pKa values, like Ka1, Ka2, Ka3, etc. You would know it's possible to dissociate the acid multiple times since it has more than 1 Ka value.

List of acids and bases that you can look through to see which are polyprotic in advance of the test (posted on the 14B website): https://lavelle.chem.ucla.edu/wp-conten ... _Bases.pdf

-Vivek