Dissociation of Weak/Strong Acids/Bases

[enervate]

From the Acids & Bases section in TBR General Chemistry:

KOH is a strong base while KOAc is a weak base. Both KOH and KOAc salts are comprised of one cation and one anion. As such, they will both completely dissociate into water.

Hydrofluoric acid, HF, is a weak acid so it only partially dissociates in water.

Why the discrepancy between the weak base, KOAc, completely dissociating into water and the weak acid, HF, only partially dissociating in water?

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[QrtrLifeCrisis]

From the Acids & Bases section in TBR General Chemistry:

Why the discrepancy between the weak base, KOAc, completely dissociating into water and the weak acid, HF, only partially dissociating in water?

KOAc and KOH are potassium salts. From the solubility rules, you know that that K+ salts are always soluble.

HF is a weak acid, meaning that the F- likes to hold on to its proton due to its electronegativity.

These are two different concepts.

 

[enervate]

Cheers!

 

[gettheleadout]

KOAc and KOH are potassium salts. From the solubility rules, you know that that K+ salts are always soluble.

HF is a weak acid, meaning that the F- likes to hold on to its proton due to its electronegativity.

These are two different concepts.

Also, KOAc is a double whammy for knowing your solubility rules because acetate salts are generally soluble as well!

One note about HF though, the electronegativity of the H-F bond would actually predict a stronger acidity than the other haloacids, because greater EN means more a polar bond, leading to less activation energy for heterolytic cleavage. The reason the trend for haloacidity is the opposite is because the polarizability of the conjugate anion contributes more to the stability of the conjugate base than the EN does to the dissociation.

HF is weak because F- is unstable by itself, and the net effect is that most HF remains as-is in solution.

 

[QrtrLifeCrisis]

Yep, F- is a tricky littler bastard.