Molal cryoscopic constant

The quantity MiRTojAfH is the molal cryoscopic constant of the solvent, given in the limit as ->0 by... 

SAQ 5.6 Pure water has a normal freezing point of 273.15 K. What will be the new normal freezing point of water if 11 g of KCI is dissolved in 0.9 dm3 of water The cryoscopic constant of water is 1.86 Kkg-1 mol-1 assume the density of water is 1 gem-3, i.e. molality and molarity are the same. 

You dissolve 90 g of sucrose (molar mass = 342 g/mol) in 1000 g of water. What is the molality of the solution If the cryoscopic constant for water is 1.9 degrees/molal, what is the freezing point of the solution ... 

The cryoscopic method was used in Hantzsch s original work 53, 54) and was later developed by Hammett and Deyrup 56) and by Gillespie et al. 48). Sulfuric acid freezes at 10.371 C and has a relatively large molal freezing-point depression or cryoscopic constant fc = 6.12 32). It is thus a convenient solvent for cryoscopic measurements provided that adequate precautions are taken to prevent absorption of water from the atmosphere. From freezing-point measurements the number, v, of moles of particles (ions and molecules) produced by one mole of any solute may be obtained. Some examples are given in Table IV. 

Cryoscopic constant (T ) - The constant that expresses the amount by which the freezing point of a solvent is lowered by a non-dissociating solute, through the relation AT = m, where m is the molality of the solute. 

Following Eq. (8.12) the freezing point depression is proportional to the cryoscopic constant and the concentration of the solute (m2 (mol/kg)) in the molality scale. Since the cryoscopic constant K ry of the solvent depends on the molar mass, the melting temperature T and the enthalpy of fusion, the various liquids show different values. From Eq. (8.12) it can be seen that the measurement of the freezing point depression allows the determination of the molar mass of unknown compounds, if the melting temperature and the enthalpy of fusion is known. 

Note that the melting point depression of a solution is only dependent of molality of solute but not of the chemical composition of it and can be used to determine the molality of the solute and its molar mass. A selection of cryoscopic constants is given in Table 20.10. 

The molal freezing-point depression constant or cryoscopic constant, Kf, is defined... 

This paper reports cryoscopic measurements for NiS04 aqueous solutions (0.00 > t /°C > - 0.21), and demonstrates the dependence of the calculated value of K on the assumptions in the complexation model. Based on the arguments of Brown and Prue, it is clear that use of the SIT as is done in the TDB project imposes constraints on the data analysis, and that these constraints should lead to a specific value for K. However, recalculations show that the association constant is also strongly dependent on the concentration at which the data set is truncated. For the purposes of the present review, recalculations were done using the SIT, but only results for molalities < 0.03 were used in the selection of the value of log . When data for higher concentrations were included, the calculated value for the association constant increased, and log,Q = 300 was obtained if the entire data set was used. 

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