We’re being asked to determine the mass of ethylene glycol (C2H4(OH)2) that must be added to 400.0 g water to get a solution with a freezing point of –8.35 ˚C.
Recall that the freezing point of a solution is lower than that of the pure solvent and the change in freezing point (ΔTf) is given by:
The change in freezing point is also related to the molality of the solution:
i = van’t Hoff factor
m = molality of the solution (in m or mol/kg)
Kf = freezing point depression constant (in ˚C/m)
Recall that the molality of a solution is given by:
For this problem, we need to do the following:
Step 1: Calculate for ΔTf.
Step 2: Determine the molality of the solution.
Step 3: Calculate the mass of C2H4(OH)2 needed.
How many grams of ethylene glycol, C 2H4(OH)2, must be added to 400.0 g of water to yield a solution that will freeze at -8.35 °C?
a) 37 g
b) 111 g
c) 75 g
d) 151 g
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