Boiling point elevation constant table

C. The boiling-point-elevation constant of 0.512°C kg/mole would be expected to raise the B.P. 0.0256°C for a 0.05 m solution when i = 1. The data show that the boiling-point elevation is 0.0255°C. This agrees with the theory. Therefore, C6Hi206 does not dissociate. With few or no ions in solution, poor electrical conductivity is expected. This is supported by the evidence in the table. 

What is the molality of an aqueous glucose solution if the boiling point of the solution at 1 atm pressure is 101.27°C The molal boiling-point-elevation constant for water is given in Table 11.4. 

TABLE 2. Freezing-point depression and boiling-point elevation constants... 

Table 3.6 lists Kf and Kb for several solvents. In general, the higher the molar mass of the solvent, the larger the values of Kf and Kb. If the freezing point depression and boiling point elevation constants are known, the molecular weight of the dissolved solute, M2, can be determined ... 

The boiling-point elevation constant for water is 0.512°C/m (see Table 15.3). Thus,... 

TABLE 17.5 Molal Boiling-Point Elevation Constants (Kb) and Freezing-Point Depression Constants (Kf) for Several Solvents... 

The molal boiling point elevation constant, S), is the difference in boiling points between aim nonvolatile, nonelectrolyte solution and a pure solvent. It is expressed in units of °C/w and varies for different solvents. Values of A j, for several common solvents are found in Table 15-4. Note that water s A j, value is 0.512°C/w. This means that a m aqueous solution containing a nonvolatile, nonelectrolyte solute boils at 100.512°C, a temperature 0.512°C higher than pure water s boiling point of 100.0°C. 

The term A7)j represents the elevation of the boiling point of the solvent, that is, the boiling point of the solution minus the boiling point of the pure solvent. The m is the molality of the solute, and is a proportionality constant called the molal boiling point elevation constant. This constant is different for different solvents and does not depend on the solute (Table 14-2). 

The molal boiling point elevation constant, Kb> thus can be calculated from the properties of the solvent, namely 7J, Mi, and AHyap. Table 5.3 gives Kt values calculated in this way, as well as experimental Kt, values obtained by direct rneasurement of ATb for solutions of known molality. The agreement is quite satisfactory. 

Table 5.3 Molal Boiling-Point Elevation Constants...

Table 12.2 lists values of A), for several common solvents. Using the boiling-point elevation constant for water and Equation (12.6), you can see that if the molality of an aqueous solution is 1.00 m, the boiling point will be 100.52°C. 

Using Equations 9.21 and 9.24 and data from Tables 7.7 and 7.8, calculate the freezing-point depression and boiling-point elevation constants for diethyl ether. 

The magnitude of Ky, which is called the molal boiling-point-elevation constant, depends only on Ihe solvent. Some typical values for several conunon solvents are given in Table 13.4 . 

Use the data in Table 12.4 to evaluate the molal freezing-point depression constant and the molal boiling-point elevation constant for H2O at a pressure of 1 bar. 

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 proportionality constants Kb and Kf, called the boiling-point elevation constant and the freezing-point depression constant, respectively, are characteristic of the solvent. Constants for some common solvents are listed in Table 10.2. 

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 elevations are directly proportional to the molality of a solution, but chemists have found that some solvents are more susceptible to this change than others. The formula for the change in the boiling point of a solution, therefore, contains a proportionality constant, abbreviated K, which is a property determined experimentally and must be read from a table such as Table 13-2. The formula for the boiling point elevation is... 

TABLE 4.6 Molecular Elevation of the Boiling Point Ebullioscopic constants... 

A knowledge of the boiling-point elevation and the appropriate constant from Table 1-4 allows one to calculate the molality of the solution, and this figure coupled with the weight of material added gives the molecular weight. The values thus determined are usually accurate to about 10 per cent. 

TABLE 11.2 Boiling-Point Elevation and Freezing-Point Depression Constants... 

The boiling-point constant, kb, depends on the solvent and has units of K-kg-mol (Table 8.8). -> The boiling-point elevation equation holds for nonvolatile solutes in dilute solutions that are approximately ideal. 

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