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15_05_86 - Compound E f/K kg mol –1 Acetamide 3.92 Acetic...

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CRYOSCOPIC CONSTANTS FOR CALCULATION OF FREEZING POINT DEPRESSION The freezing point T f of a dilute solution of a non-volatile, non- dissociating solute is depressed relative to that of the pure solvent. If the solution is ideal (i.e., follows Raoult’s Law), this lowering is a function only of the number of particles of solute present. Thus the absolute value of the lowering of freezing point ∆ T f can be ex- pressed as T f = E f m 2 where m 2 is the molality (moles of solute per kilogram of solvent) and E f is the Cryoscopic Constant, a characteristic property of the solvent. The Cryoscopic Constant may be calculated from the re- lation E f = R T f 2 M /∆ fus H where R is the molar gas constant, T b is the freezing point tem- perature (absolute) of the solvent, M the molar mass of the solvent, and ∆ fus H the molar enthalpy (heat) of fusion of the solvent. This table lists cryscopic constants for selected substances, as cal-
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Unformatted text preview: Compound E f /K kg mol –1 Acetamide 3.92 Acetic acid 3.63 Acetophenone 5.16 Aniline 5.23 Benzene 5.07 Benzonitrile 5.35 Benzophenone 8.58 (+)-Camphor 37.8 1-Chloronaphthalene 7.68 o-Cresol 5.92 m-Cresol 7.76 p-Cresol 7.20 Cyclohexane 20.8 Cyclohexanol 42.2 cis-Decahydronaphthalene 6.42 trans-Decahydronaphthalene 4.70 Dibenzyl ether 6.17 p-Dichlorobenzene 7.57 Diethanolamine 3.16 Dimethyl sulfoxide 3.85 Compound E f /K kg mol –1 1,4-Dioxane 4.63 Diphenylamine 8.38 Ethylene glycol 3.11 Formamide 4.25 Formic acid 2.38 Glycerol 3.56 Methylcyclohexane 2.60 Naphthalene 7.45 Nitrobenzene 6.87 Phenol 6.84 Pyridine 4.26 Quinoline 6.73 Succinonitrile 19.3 1,1,2,2-Tetrabromoethane 21.4 1,1,2,2-Tetrachloro-1,2-difluoroethane 41.0 Toluene 3.55 p-Toluidine 4.91 Tribromomethane 15.0 Water 1.86 p-Xylene 4.31 15-28...
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