Cryoscopic constants table

Their high cryoscopic constants (Table IV) also make them suitable for determining molecular and ionic weights. 

TABLE 11.2 Molecular Lowering of the Melting or Freezing Point Cryoscopic constants. 

In Table 4.9A, a range of compounds and their cryoscopic constants are recorded. All of the same data are included in Table 4.9B but they are rearranged in order of increasing melting point at the left and decreasing Kf at the right. 

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. 

There are a number of solvents for which some cryoscopic data are available but which have not been studied extensively. The melting point, cryoscopic constant and literature references to these solvents and those discussed above are included in Table 2.10.1. 

One possible way of doing this is to purchase and to store the solvent mixed with an acceptable impurity thus lowering the freezing point of the mixture. If this is practicable it will normally be a solvent that has a high cryoscopic constant (F) so that the added impurity required will only be a small addition (Table 13.1). The cryoscopic constant is defined as the depression of the freezing point of a solvent when a gram mole of any substance is dissolved in 100 g of the solvent. 

Table 1-14 shows the cryoscopic constants C. for some solvents. 

Freezirig prant curves were computed for pora- and o/rfio-xylene using Eq. (11.2-6) (the van t Hoff equation) and Eq. (11.2-7) which ured cryoscopic constants. Data from Table 11.2-1 were used in the equations and calculated equilibriom compositions are shown as a Ainction of temperature in Table 11.2-2. The computed liquid compositions are nearly identical in the high concentration range and diverge... 

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. 

Shatenshtein et al.5ia also found a similar dependence of rate coefficient upon the concentrations of stannic chloride and acetic acid in the dedeuteration of [l,4-2H2]-durene in benzene. Rate coefficients increased linearly with increasing stannic chloride concentration and at a constant value of this the rate increased only slightly with increasing acetic acid concentration, except at high concentrations of the latter when the rate then decreased (Table 155). Cryoscopic mea-... 

Table 5.3 Sample values of boiling and freezing points, and cryoscopic and ebullioscopic constants...

Hence by evaluating xa from cryoscopic measurements the constancy of Kf. in this formula can be tested. For the system phenylacetic acid 4-nitrobenzene the data in table 26.1 show that is not constant, but that the data are in closer agreement with the assumption of dimer association. However, the figures in table 26.2 show that the equations for dimerisation are not consistent with the behaviour of benzyl alcohol in nitrobenzene, but that in this case is practically constant. This indicates that benzyl alcohol associates in nitrobenzene to form a series of association complexes. 

Table 12.1 Cryoscopic and ebullioscopic constants of some solvents (from Lide D R (ed) (2008) CRC Handbook of Chemistry and Physics, 89th edn. CRC Press, Boca Raton).

Table 2.7. Cryoscopic and ebullioscopic constants for some common solvents...

In solution, the racemic tartaric acid may be represented as C02H-(CH0H)2-CO2H, as is indicated by its cryoscopic depression and its ionization constant its solubility is controlled, however, by the molecular complexity of the solid. (See Table VI.)... 

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