Distinguishing strong vs. weak acids

[juliaddc]

I understand that for the most part, it's best to just memorize the strong acids, but I'm having a hard time understanding dissociation. I know that strong acids will completely dissociate in water, but why is that, and why is it that weak acids don't?
For example, in the Achieve assignment for the week I saw, HCN, but I don't understand what it is about the molecule that will maintain HCN instead of dissociating into H+ and CN-.

Thank you!

[305920501]

Strong acids fully dissociate in an aqueous solution because the equilibrium favors their deprotonation so strongly. There is technically still some movement with the conjugate base potentially gaining a hydrogen and becoming an acid again, but we represent it with a forward reaction and call it a strong acid because for the most part, the strong acid is just deprotonated. Weak acids, on the other hand, are considered this because only a small fraction of the molecules donate their protons. For example, with HCN, the equilibrium is dynamic, meaning the protons can infinitely exchange back and forth between HCN and H2O with constant, low concentration of CN- and H3O+ ions. It is easiest to try to understand this process but memorize which acids are strong acids to differentiate.

[Shaniya Kerns 4D]

A strong acid is able to disassociate completely in an aqueous solution due to being completely ionized because their conjagate bases are weaker than water, having more hydrogen ion concentration. Weak acids tend to be more partially ionized due to having less concentration of hydrogens therefore competing with water for protons. Hope this helps.

[Ashley Peterson 2C]

Hello!
Answering the question on why strong acids will completely dissociate in water and weak acids won't, I believe it's because strong acids have a high affinity for donating protons..in this case H+ ions. (+ highly stable conjugate bases) When weak acids are added to water, only a fraction of the acid molecules would ionize (and have weaker conjugate bases), and therefore release a limited number of protons.
And for how the molecule will maintain HCN rather than dissociating into H+ and CN-,I think it's because HCN has a polar bond and will be more electronegative than hydrogen. HCN is also a weak acid and its dissociation into H+ and CN- wouldn't be as favorable as it is for strong acids.
I hope this helps!