HSAB: Hard Soft Acid Base | Ferdinand's Curiousity

[fairburn96]

Hi guys, my name is ferdinand. I'm curious about HSAB, especially to predict where the reaction goes.
Exp: HI + NaF >>> HF + NaI
H is hard acid
I IS soft base
Na is hard acid
F is hard base, and

HF Is hard.hard
NaI Is hard soft.
The reaction will goes to right or left? And why?
And since hard acid like to bind hard base, why NaI formed?
Thank you...
Terima kasih.And how about the borderline? Is it count as hard or soft?

 

[insightful]

Have you calculated the equilibrium constant? My quick look says the reaction goes to the left, as you suspect.

 

[Borek]

In water? Or a solid and a gas?

 

[insightful]

In water? Or a solid and a gas?

Good question. I assumed water. OP?

 

[Borek]

I assumed water.

Then it should go to the right, HF is a weak acid.

 

[insightful]

Then it should go to the right, HF is a weak acid.

I used DeltaG_f of (all aqueous at 25C):
-129 kcal/gmol for NaF
-71 for NaI
-12 for HI
-66 for HF

and got DeltaG_rxn = +4kcal/gmol and using DeltaG = -RTlnK_eq, got K_eq = 1.2E-3 indicating left side reactants at higher concentrations than right side products.

 

[Borek]

Well, it depends on what your starting material is. Yes, in general the equilibrium is to the left, but if you add HI to the NaF solution, fluoride gets protonated and the shift is to the right.