Freezing-point data

Carbon disulfide is completely miscible with many hydrocarbons, alcohols, and chlorinated hydrocarbons (9,13). Phosphoms (14) and sulfur are very soluble in carbon disulfide. Sulfur reaches a maximum solubiUty of 63% S at the 60°C atmospheric boiling point of the solution (15). SolubiUty data for carbon disulfide in Hquid sulfur at a CS2 partial pressure of 101 kPa (1 atm) and a phase diagram for the sulfur—carbon disulfide system have been published (16). Vapor—Hquid equiHbrium and freezing point data ate available for several binary mixtures containing carbon disulfide (9). 

Physical and Chemical Properties - Physical State at 15 C and 1 atm. Liquid Molecular Weight 237.16 (solute orUy)-, Boiling Poiru at 1 atm. 12111001373 Freezing Point Data not available Critical Terrqterature Not pertinent Critical Pressure Not pertinent Specific Gravity 1.54 at 20°C (liquid) Vapor (Gas) Density Not pertinent Rcttio of ecific Heats of Vapor (Gas) Not pertinent Latent Heat of Vaporization Not pertinent Heat of Combustion Not pertinent Heat of Decomposition Not pertinent. 

Plan (1) Evaluate the van t Hoff factor, i, from the freezing point data. 

From a thermodynamic standpoint, freezing point measurements and isopiestic measurements are similar since both yield directly the activity of the solvent. When done carefully, freezing point data can generate activity coefficient values at concentrations down to 0.001 molal. During the first half of this century, much activity coefficient data was obtained from freezing point measurements. However, the popularity of this technique has decreased and is seldom used for aqueous solutions at the present time. 

Moyers and Rousseau(25) have used equations 15.5 and 15.6. to calculate the freezing point data for o- and p-xylenc shown in Table 15.3. 

Figure 19.11. A plot of —(1 — g)/m2 against from the freezing point data for potassium nitrate (KNO3) solutions in water. Data from G. Scatchard, S. S. Prentice, and P. T. Jones, J. Am. Chem. Soc. 54, 2690 (1932). See Equation (19.63).

Prentice, J. H. 1978. Freezing point data on aqueous solutions of sucrose and sodium chloride and the Hortvet test A reappraisal. Analyst 103, 1269-1273. 

Table A.2. Sulfuric Acid Freezing Point Data. Sulfuric acid freezing point temperature versus mass % H2S04 in acid. Source Gable, C.M., Betz, H.F. and Maron, S.H. (1950) Phase equilibria of the system sulfur trioxide-water, Journal of the American Chemical Society, Vol. 72, 1445 1448. www.chemistry.org...

ACTIVITY OF SOLVENT AND SOLUTE FROM LOWERING OF FREEZING POINT DATA... 

The following freezing-point data are reported for aqueous solutions of cane sugar ... 

Boiling-point data tor a solution can be used to obtain the molecular weight of the solute in the same way as the freezing-point data. 

Rosenlieim, Zeitsch. anorg. Chem., 1907, 54, 97, where electrical conductivity and freezing-point data for solutions of this salt are also given. 

Another test of this treatment is to employ freezing point data in the following way. We have on the one hand (26.58)... 

D is correct. A greater concentration of particles lowers freezing point more. The freezing point data was collected and recorded for the cyclohexane solution, not the crushed ice solution. 

Calculation of Total Osmotic Pressure from Freezing Point Data — From the lowering of fieezing point, At the total osmotic pressure may be readily and accurately calculated by means of the equation (Washburn, loc cit)—... 

Solution of the Equations—The object before us is to calculate, m the case of a strong electrolyte such as KC1, the osmotic pressure exerted by the undissociated molecules and by the 10ns (as distinct from the molecules) m older to see whether one sort or both sorts deviate from van t Hoff s law, and thereby cause the law of mass action to be inapplicable It is assumed that the concentration of the 10ns Ct and of the undissociated molecules C can be obtained accurately from the conductivity expression, the symbol y being used to denote the ionisation coefficient determined by this method When the terms C, and C occur, it is to be understood that they are determined directly by conductivity At the same time we require to know the total osmotic pressure tr of the solution and this is to be understood as directly obtainable from the freezing point data by means of equation (4)... 

Inspection of the figuies shows that equation (17) reproduces the experimental data with considerable accuracy This agreement, as Bates pomts out, is not proof independent of that drawn from the freezing-point data that equation (13) expresses the behaviour of ions of potassium chlonde It shows that the freezing-point data and the electro-motive foice data are consistent with each other... 

Bates points out that the mistake is often made of calculating the degree of dissociation from freezing-point data by usmg the empirical expression w = zRT[Pg.211]

This relation must hold if the mass law is obeyed By eliminating C, and C from this equation and from the thermodynamic equation (i), (viz 2dirJC, - dirujCu = o), it is seen that the necessary and sufficient condition that the law of mass action should hold is that at all concentrations dmUC = dirJdCu Now the computation of van t Hoff s factor i from freezing-point data, and the consequent calculation of the degree of ionisation on this basis assumes that the ions and the undissociated molecules are normal That is, it assumes dirJdC, = dirJdCu = RT... 

This does not refer to the criticism of the use of the van t Hoff factor 1 in connection with freezing point data, which is quite indefensible, as it involves two simultaneous assumptions which are incompatible The proof, just given, of the invalidity of the t mode of calculating dissociation is quite independent of the accuracy or inaccuracy of conductivity results... 

The values of a in the KC1 column enclosed in brackets are obtained from Harned s data (Journ Amer Chem Soc, 38, 1989 (1916)) The values of a in the case of KCI should be compared with the values calculated from the freezing point data by Lewis and Lmhart, quoted later, the values obtained from the freezing point are somewhat higher than those obtained from e m f data Theoretically, they should be identical, except in so far as temperature may exert a small effect The e m f data refer to 2 50 C, the freezing point data to 0° C approximately ]... 

Calculation of the Activity of Ions as a Function of Dilution, from Freezing Point Data... 

As already pointed out the apparent molecular weights of dissolved substances—and consequently the thermodynamic degree of ionisation or activity coefficient a in the case of an electrolyte—as determined by freezing point data are necessarily those which would be obtained from direct measurements of osmotic pressure or from emf measurements, since these different modes of measurement are related thermodynamically It will be recalled that the activity coefficient a for an ion is less than the y value over a wide range of concentration... 

The authors are also indebted to Mr. John De Guzman for assistance in obtaining the flash point and freezing point data. 

To calculate the molecular weight of the unknown compound, we find the number of moles that is represented by the 1.20 grams of unknown compound. We first use the freezing point data to find the molality of the solution. The molality relates the number of moles of solute and the mass of solvent (known), so this allows us to calculate the number of moles of unknown. 

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