So I saw this equation for the freezing point depression, when you add a solute: $\Delta T= K_\mathrm fmi$
Where,
- $\Delta T =$ The freezing point depression
- $K_\mathrm f =$ The freezing point depression constant (Cryoscopic constant)
- $m =$ Molality
- $i =$ van't hoff factor.
I read online that $\ce{CaCl2}$ would be better than $\ce{MgCl2}$, but I cannot understand why in the terms of this formula since $i$ for both of them is the same and $K_\mathrm f$ seems to be independent of the solute since I saw values of $K_f$ of water online. (without any solute given)
So, could someone answer why this happens? Because it seems to me that the $K_\mathrm f$ could be the only factor that would explain this. Specifically I would like to know if the charge or the electronegativity of the dissolved ions would make a difference.