Cryoscopy Freezing Point Depression

Methods for the determination of Molecular weight based on colligative property are vapour-pressure lowering, boiling point elevation (ebulliometry), freezing-point depression (cryoscopy), and the Osmotic pressure (osmometry). 

The number average molecular weight determines the colligative properties (i.e., those which depend only on the number of dissolved molecules) of polymer solutions. Measurements of freezing point depression (cryoscopy) or... 

The constitution of the thorium(lV) carbonate complex formed at high carbonate concentration has been determined by cryoscopy. This is a method that provides information about the number of solute particles in solution and for the case of complex formation reactions, the change in this number as a result of complex formation, e.g. for the reaction Th" + 5CO3 Th(C03)5 there is a decrease of five. The authors have determined the molar freezing point depression and this is used to test the stoichiometry of the complexes formed. One important conclusion from this study is that the experimental data are only consistent with the stoichiometry Th(C03)j". Experimental data of this type caimot be made in a medium of constant ionic strength and it is also not possible to determine equilibrium constants. However, the proposed stoichiometiy is in agreement with that proposed in a large number of other studies. 

Cryoscopy Number average molecular weight Freezing point depression [Pg.124]

In the next section we shall discuss the physical properties and structure of the more important of the organic solvents mentioned in later chapters. In Chapter 2, the thermodynamic properties of solutions are discussed. Firstly, C. M. Criss discusses solubility and calorimetric measurements. In planning new work with unfamiliar solvents the extent of solubility of compounds is a primary consideration. Viscosity is also considered under this heading since although it is a transport property it is often used in the same way as thermodynamic measurements, to infer structural properties. An important technique for obtaining thermodynamic quantities of certain solutions is cryoscopy, the measurement of freezing point depressions, and this is discussed by R. Garnsey and J. E. Prue. Measurement of the e.m.f.s of suitable cells... 

When you dissolve something in water, for example, salt, the solution has slightly different properties than pure water. For example, a salty solution boils at a higher temperature and freezes at a lower temperature than pure water. Physical chemists have established that these changes, from pure solvent to solution, depend on the number of particles of the solute and not so much on the type of solute. The common name for these effects is colligative properties of mixtures and solutions. Outside of a physical chemical laboratory those of us who live in colder climates are well familiar with the phenomenon of freezing point depression or cryoscopy. This is also a physical chemical experiment actively practiced by the fish swimming in arctic seas. 

Cryoscopy n. Measurement of polymer molecular weight based on freezing point depression. 

Calculation of the freezing-point depression of the solvent and hence the molecular weight of the solute by this method proceeds exactly the same way as for the boiling-point elevation. For cryoscopy of ideal solutions, equations corresponding to those for Ar and ke are AT/ = -kftnz and = (RT Mi)l(l000Lf), where ATf = T - Tf Hhe freezing-point depression. Tf is the... 

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