In the Freezing Point Depression experiment, you will calculate the colligative
ID: 481456 • Letter: I
Question
In the Freezing Point Depression experiment, you will calculate the colligative molality of the solutions you produce, the freezing point depression, and the predicted boiling point of the resulting solutions. This question will give you practice doing this before you come to lab.
In an experiment, you use 9.000 g of solvent (FP = 91.7°C; Kf = 5.1°C/m) and 0.560 g of solute (molecular mass = 223.65 g/mol).
SIGNIFICANT FIGURES MATTER
(a) How many moles of solute have you used? 40Z .00426 x mol (b) What is the colligative molality of the solution formed? 4.0 (c) What is the predicted freezing point depression ATf? 4.0 OC (d) What is the predicted freezing point of the solution formed? 4.0 OCExplanation / Answer
(a) Moles of solute = mass/molar mass of solute
= 0.560/223.65
= 2.50*10^-3mol
(b) Molality = moles of solute/mass of solvent in kg
=2.50*10^-3/0.009000
= 0.28 m
(c) DTf = Kf x molality
= 5. x 0.277
= 1.385 deg C = 1.39 deg C
(d) Freezing point of solution = freezing point of solvent - DTf
= 91.7 - 2.64
= 89.06 deg C = 89.1 deg C