Wednesday, March 7, 2018

homework due 3.8.18

Read
  Chapter 15.10, pp 495 - 496
Do
  Problems 50, 51, 59

Calculation of Freezing Point Depression

If the solution is treated as an ideal solution, the extent of freezing-point depression depends only on the solute concentration that can be estimated by a simple linear relationship with the cryoscopic constant ("Blagden's Law"):
ΔTF = KF · b · i,
where:
  • ΔTF, the freezing-point depression, is defined as TF (pure solvent) − TF (solution).
  • KF, the cryoscopic constant, which is dependent on the properties of the solvent, not the solute. (Note: When conducting experiments, a higher KF value makes it easier to observe larger drops in the freezing point. For water, KF = 1.853 K·kg/mol.[7])
  • b is the molality (moles solute per kilogram of solvent)
  • i is the van 't Hoff factor (number of ion particles per individual molecule of solute, e.g. i = 2 for NaCl, 3 for BaCl2)

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