Chemistry Practice Problems Freezing Point Depression Practice Problems Solution: What is Kf for water if the freezing point was low...

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Solution: What is Kf for water if the freezing point was lowered to -12°C once 30 g of Sodium Chloride was added to 150 g of water?

Problem

What is Kf for water if the freezing point was lowered to -12°C once 30 g of Sodium Chloride was added to 150 g of water?

Solution

We’re being asked to find the Kf (freezing point depression constant) of water if its freezing point decreased to -12°C when NaCl was dissolved in it. We’re going to use the Freezing Point Depression equation to calculate for Kf.


∆Tf = change in freezing point = Tf pure solvent –Tf solution
Kf = freezing point depression constant
i = van' t Hoff factor of the solute = no. of ions
m = molality


Let’s first calculate the molality of the solution. 

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