How do you calculating freezing point from molality?

Answer 1

One of the colligative properties of solutions is freezing-point depression.

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 freezing point depression is given by

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

where

  • #DeltaT_f# represents the change in freezing point of the solution

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

  • #m# is the molality of the solution, the number of moles of solute dissolved per kilogram of solvent:

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

  • #K_f# is the 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 change in freezing point, to find the new freezing point, you subtract the #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 negative (possibly because the constant #K_f# was negative). Just know that the magnitude of the #DeltaT_f# quantity (regardless of sign) represents by how much the freezing point is lowered.)

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Answer 2

To calculate the freezing point depression from molality, you can use the formula:

ΔTf = Kf * m

Where: ΔTf = freezing point depression (in °C) Kf = cryoscopic constant (specific to the solvent, typically given in units of °C kg/mol or °C/m) m = molality of the solute (moles of solute per kilogram of solvent)

Multiply the cryoscopic constant (Kf) by the molality (m) of the solute to find the freezing point depression (ΔTf).

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

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