How do you calculating freezing point from molality?

Uno di proprietà colligative of Solutions is depressione del punto di congelamento.

This phenomenon helps explain why adding salt to an icy path melts the ice, or why seawater doesn't freeze at the normal freezing point of #0# #""^"o""C"#, or why the radiator fluid in automobiles don't freeze in the winter, among other things.

The equation for depressione del punto di congelamento è dato da

#ulbar(|stackrel(" ")(" "DeltaT_f = imK_f" ")|)#

where

• #DeltaT_f# rappresenta la change in freezing point della soluzione

• #i# è chiamato fattore van't Hoff, which is essentially the number of dissolved particles per unit of soluto (for example, #i = 3# for calcium chloride, because there is #1# #"Ca"^(2+) + 2# #"Cl"^(-)#).

• #m# Monteverede vecchio è molality of the solution, the number of moles of solute dissolved per chilogrammo of solvente:

#"molality" = "mol solute"/"kg solvent"#

• #K_f# Monteverede vecchio è molal freezing-point depression constant for the solvent, which the following table lists some values for certain solvents:

(the far-right column shows the #K_f#)

Once you've calculated the cambiamento in freezing point, to find the new freezing point, Si sottrarre il #DeltaT_f# quantity from the normal freezing point of the solvent:

#ul("new f.p." = "normal f.p." - DeltaT_f#

(I'd like to point out that depending on how you're taught, the #DeltaT_f# quantity may be negativo (possibly because the constant #K_f# was negative). Just know that the grandezza tutte lungo la #DeltaT_f# quantity (regardless of sign) represents by how much the freezing point is lowered.)