Benzene boiling-point elevation

Because of the scarcity of electronic paramagnetic resonance data, and because of the frequent unreliability of the data from paramagnetism, boiling point elevation, spectrophotometry, and ortho-para hydrogen conversion, most published radical dissociation constants can be accepted only with reservations. An error of 50 % is not at all improbable in many cases. We are therefore not yet in a position to explain, or rather to test our explanations of, small differences in dissociation constants. Table I shows the values of K corresponding to various hexaarylethanes in benzene at 25°. Because of the order of magnitude differences in Table I, however, it is likely that some of the expected large effects, such as steric and resonance effects, exist. 

Boiling point elevation K, A/f, mono-, dicarboxylic adds in benzene, 80°C. 

A student dissolves 0.500 mol of a nonvolatile, nonelectrolyte solute in one kilogram of benzene (CgHg). What is the boiling point elevation of the resulting solution ... 

A solution containing 4.22 g of a nonelectrolyte polymer per hter of benzene solution has an osmotic pressure of 0.646 torr at 20.0°C. (a) Calculate the molecular weight of the polymer, (b) Assume that the density of the dilute solution is the same as that of benzene, 0.879 g/mL. What would be the freezing point depression for this solution (c) Why are boiling point elevations and freezing point depressions difficult to use to measure molecular weights of polymers ... 

What information must you know to calculate the boiling point elevation of a solution of hexane in benzene (Chapter 14)... 

The constant of proportionality, Ki, (called the boiling-point-elevation constant), depends only on the solvent. Table 12.3 lists values of K, as well as boiling points, for some solvents. Benzene, for example, has a boiling-point-elevation constant of 2.61°C/m. This means that a 0.100 m solution of a nonvolatile, undissociated solute in benzene boils at 0.261°C above the boiling point of pure benzene. Pure benzene boils at 80.2°C, so a 0.100 m solution boils at 80.2°C + 0.261°C = 80.5°C. 

The molal boiling-point elevation constant of benzene is 2.5°C/m. A solution of 15.2 g of unknown solute in 91.1 g benzene boils at a temperature 2.UC higher than the boiling point of pure benzene. Estimate the molar mass of the solute. 

The dehydrogenation reaction produces crude styrene which consists of approximately 37.0% styrene, 61% ethylbenzene and about 2% of aromatic hydrocarbon such as benzene and toluene with some tarry matter. The purification of the styrene is made rather difficult by the fact that the boiling point of styrene (145.2°C) is only 9°C higher than that of ethylbenzene and because of the strong tendency of styrene to polymerise at elevated temperatures. To achieve a successful distillation it is therefore necessary to provide suitable inhibitors for the styrene, to distil under a partial vacuum and to make use of specially designed distillation columns. 

When 8.8 g of a mystery compound is added to 42.1 g of benzene, the boiling point is elevated to 81.9°C. What is the molecular mass of this mystery compound ... 

The molar depression of the freezing-point for the trichloride in benzene 4 is 0-686° and the molar elevation of the boiling-point in the same solvent is about 4-5°. 

The ethyl and methyl esters have been prepared by the usual methods. Thus (C2H5)4P207 by the action of C2H5I on Ag4P207 at 100° C. The product was a liquid soluble both in water and in alcohol.3 The elevation of the boiling-point of benzene by this ester corresponded to simple molecules.4 The decomposition of the ester on heating supports the asymmetrical constitution —... 

At room temperature there are no known solvents for SPS. Even though the good solvents for atactic polystyrene such as toluene, benzene, tetrahydrofuran and dichloroethane can swell SPS at room temperature. Some of these solvents dissolve SPS at elevated temperatures, close to their boiling point. For example, a 5-10% by weight solution can be prepared by heating the polymer with trichlorobenzene at 160 °C with agitation. 

Starch palmitate is prepared by treating 1 part of starch in a mixture of 4 parts of benzene and 1.8 parts of pyridine with 6 parts of palmitoyl chloride and 4 parts of benzene for thirty minutes at 60° and precipitating the product with ethanol. Quinoline may be substituted for the benzene and pyridine. Because of the high boiling point of quinoline, an elevated esterification temperature can be used and triesters produced in about three hours. 

M (gmol ) Osmotic pressure (mm benzene) Lowering of vapour pressure (mm Hg) Elevation of boiling point (K) Depression of freezing point (K)... 

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