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15_04_86 - ed from data in the table “Enthalpy of...

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EBULLIOSCOPIC CONSTANTS FOR CALCULATION OF BOILING POINT ELEVATION The boiling point T b of a dilute solution of a non-volatile, non- dissociating solute is elevated relative to that of the pure solvent. If the solution is ideal (i.e., follows Raoult’s Law), the amount of el- evation depends only on the number of particles of solute present. Hence the change in boiling point ∆ T b can be expressed as T b = E b m 2 where m 2 is the molality (moles of solute per kilogram of solvent) and E b is the Ebullioscopic Constant, a characteristic property of the solvent. The Ebullioscopic Constant may be calculated from the relation E b = R T b 2 M /∆ vap H where R is the molar gas constant, T b is the normal boiling point temperature (absolute) of the solvent, M the molar mass of the solvent, and ∆ vap H the molar enthalpy (heat) of vaporization of the solvent at its normal boiling point. This table lists E b values for some common solvents, as calculat-
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Unformatted text preview: ed from data in the table “Enthalpy of Vaporization” in Section 6. Compound E b /K kg mol –1 Acetic acid 3.22 Acetone 1.80 Acetonitrile 1.44 Aniline 3.82 Anisole 4.20 Benzaldehyde 4.24 Benzene 2.64 1-Butanol 2.17 Carbon disulfide 2.42 Chlorobenzene 4.36 1-Chlorobutane 3.13 Cyclohexane 2.92 Cyclohexanol 3.5 Decane 6.10 Dichloromethane 2.42 Diethyl ether 2.20 Dimethyl sulfoxide 3.22 1,4-Dioxane 3.01 Ethanol 1.23 Ethyl acetate 2.82 Ethylene glycol 2.26 Heptane 3.62 Compound E b /K kg mol –1 Hexane 2.90 Iodomethane 4.31 Methanol 0.86 Methyl acetate 2.21 N-Methylaniline 4.3 N-Methylformamide 2.2 Nitrobenzene 5.2 Nitromethane 2.09 1-Octanol 5.06 Phenol 3.54 1-Propanol 1.66 2-Propanol 1.58 Pyridine 2.83 Pyrrole 2.33 Pyrrolidine 2.32 Tetrachloroethylene 6.18 Tetrachloromethane 5.26 Toluene 3.40 Trichloroethylene 4.52 Trichloromethane 3.80 Water 0.513 o-Xylene 4.25 15-27...
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