A 0.561 m soluation of an unknown electrolyte depresses the freezing point of water by 2.93 C . whatis the van't hoff factor for this electrolyte.
?TF = KF · b · i
- ?TF, 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.
- b is the molality (mol solute per kg 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).
i = 2.8
That's a reasonable value for something like CaCl2. Due to ion-pairing, the measured value for the van 't Hoff factor is less than the predicted value (which for CaCl2 would be 3).