Freezing points Table

Table 11.2 Molecular Lowering of the Melting or Freezing Point. 2 DRYING AND HUMIDIFICATION...

Abbreviations Used in the Table FP, freezing point BP, boiling point... 

Ciyst lliz tion. Low temperature fractional crystallization was the first and for many years the only commercial technique for separating PX from mixed xylenes. As shown in Table 2, PX has a much higher freezing point than the other xylene isomers. Thus, upon cooling, a pure soHd phase of PX crystallizes first. Eventually, upon further cooling, a temperature is reached where soHd crystals of another isomer also form. This is called the eutectic point. PX crystals usually form at about —4° C and the PX-MX eutectic is reached at about —68° C. In commercial practice, PX crystallization is carried out at a temperature just above the eutectic point. At all temperatures above the eutectic point, PX is stiU soluble in the remaining Cg aromatics Hquid solution,... 

Acetic acid containing less than 1% water is called glacial. It is hygroscopic and the freezing point is a convenient way to determine purity (7). Water is nearly always present in far greater quantities than any other impurity. Table 1 shows the freezing points for acetic acid-water mixtures. 

Table 1. Acetic Acid—Water Freezing Points...

Equally strict purity requirements apply to dimethyl terephthalate, as shown in Table 21. Freezing point is a sensitive measure of purity and can be ... 

Tlie freezing points of alkanolaiuines are moderately high as shown in Tables 1 and 2. Tlie ethaiiolamiiies, monoisopropaiiolamiiie and inono-j d -butaiiolainiiie, are colorless Hquids at or near room temperature. Di- and tiiisopropaiiolainiiie and di- and tri-J -butanolamine are wliite soHds at room temperature. 

Constants and Chemical Properties. The constants of sulfur are presented in Table 1. Two freezing points ate given for each of the two crystalline modifications. When the Hquid phase consists solely of octatomic sulfur rings, the temperature ranges at which the various modifications form are called the ideal freezing points. The temperatures at which the crystalline forms are in equiHbtium with Hquid sulfur containing equiHbtium amounts of... 

Many chemicals when added to water cause a freezing point depression, as shown in Table 1, and thus are termed antifreezes. The antifreeze properties of these chemicals vary widely as a function of their coUigative, or concentrative, properties. The reduction in freeze point depends both on the chemical itself and the concentration of the chemical in water. The freeze point depression increases as the antifreeze chemical is added to the water, until a characteristic concentration is achieved. Further addition of the antifreeze chemical to water will either result in insolubility or serve to increase the freezing point of the mixture, as illustrated in Figure 1. 

Table 1. Freeze Point Depression of Antifreeze Chemicals ...

Reduction in cation symmetry (ideally to Cl) lowers the freezing point and markedly expands the range of room-temperature liquid salts. Table 3.1-4 shows the effect of symmetry for a series of [NR4]X salts, in which all the cations contain 20 carbon atoms in the allcyl substituents [44]. 

The freezing point, temperature of maximum density, osmotic pressure and specific heat for seawater of various salinities are given in Table 21.23. 

The proportionality constants in these equations, fcb and kf, are called the moled boiling point constant and the moled freezing point constant, respectively. Their magnitudes depend on the nature of the solvent (Table 10.2). Note that when the solvent is water,... 

Table 10.3 Freezing Point Lowerings of Solutions A 7V Observed (°C) / (Calc from A TV) ... 

The data in Table 10.3 suggest that the situation is not as simple as this discussion implies. The observed freezing point lowerings of NaQ and MgS04 are smaller than would be predicted with t = 2. For example, 0.50 m solutions of NaCl and MgS04 freeze at —1.68 and —0.995°C, respectively the predicted freezing point is — 1.86°C. Only in very dilute solution does the multiplier i approach the predicted value of 2. 

How many grams of the following nonelectrolytes would have to be dissolved in 100.0 g of cyclohexane (see Table 10.2) to increase the boiling point by 2.0°C To decrease the freezing point by 1.0°C ... 

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