Freezing point depression constant table

The freezing point depression constant for water is known from experiments and can be found in tables Tf = 1.858 ° C kg/mol. To calculate the freezing point, we must first determine the molality of the... 

PROBLEM 11.20 Assuming complete dissociation, what is the molality of an aqueous solution of KBr whose freezing point is —2.95°C The molal freezing-point-depression constant of water is given in Table 11.4. 

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

Dielectric constant 5.9 at 1 MHz Freezing point depression see Table 111. 

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

Thus the molality, m, of a solution may be determined from the depression of freezing point. If the weight of solute, w, dissolved in 1 kg of solvent is known the molecular mass of the solute may be calculated from the relation M2 = 1000w/m. K iis is called the freezing-point-depression constant for the solvent. It may be readily calculated if the relevant properties of the solvent are known (Table 6.1), thus enabling the freezing-point equation to be used in a convenient form. 

In principle, any of the colligative properties can be used to find the solute s molar mass, but in practice, some systems provide more precise data than others. For example, to determine the molar mass of an unknown solute by freezing point depression, you would select a solvent with as large a molal freezing point depression constant as possible (see Table 13.5). If the solute is soluble in acetic acid, for instance, aim concentration of it depresses the freezing point of acetic acid by 3.90°C, more than twice the change in water (1.86°C). 

Table 14.6 Molal Freezing Point Depression Constants Kf) ... 

A solutions freezing point depression, ATf, is the difference in temperature between its freezing point and the freezing point of its pure solvent. Molal freezing point depression constants (Kf) for several solvents are shown in Table 14.6. For nonelectrolytes, the value of the freezing point depression is directly proportional to the solutions molality. 

The values of Kp the molal freezing-point-depression constant, for several common solvents are given in Table 13.3. For water, Kfvs 1.86 °C/m.Therefore, any aqueous solution that is 1 w in nonvolatile solute particles (such as 1 tn C6H12O6 or 0.5 m NaCl) freezes at the temperature that is 1.86 °C lower than the freezing point of pure water. 

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. 

Here Ky is the freezing-point-depression constant and depends only on the solvent. Table 12.3 gives values of Ky for some solvents. The freezing-point-depression constant for benzene is 5.07°C/m. Thus a 0.100 m solution freezes at 0.507°C below the freezing point of pure benzene. Pure benzene freezes at 5.46°C the freezing point of the solution is 5.46°C - 0.507°C = 4.95°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. 

By taking the freezing point constant for water as 1.86 from Table 9-3 and then substituting the values into the equation for freezing point depression, you obtain the change in freezing temperature ... 

---