Freezing point constants

It is often useful to know the freezing point depression of a solution. An example is given by the detection of adulteration of milk due to dilution with water. This is possible because milk as it comes from the cow has a very constant freezing point depression. Can you think of a method for accurately determining the freezing point of a solution ... 

Dielectric constant Freezing point Depression (°C) Osmolality (mosm/kg) pH... 

Nernst distribution law constant Boiling point elevation constant Freezing point depression constant Equilibrium constant Acid ionization constant Michaelis-Menten constant... 

TABLE 11.2 Molecular Lowering of the Melting or Freezing Point Cryoscopic constants. 

The fixed points in the lTS-90 are given in Tabie 11.39. Platinum resistance thermometers are recommended for use between 14 K and 1235 K (the freezing point of silver), calibrated against the fixed points. Below 14 K either the vapor pressure of helium or a constant-volume gas thermometer is to be used. Above 1235 K radiometry is to be used in conjunction with the Planck radiation law,... 

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... 

VP = vapor pressure point CVGT, constant volume gas thermometer point TP, triple point MP, melting point FP, freezing point. Note MP and FP at 101.325 Pa (1 atm) ambient pressure. 

Other purification procedures include the formation of the picrate, prepared in benzene soln and crystd to constant melting point, then decomposed with warm 10% NaOH and extracted into ether the extract was washed with water, and distd under reduced pressure. The oxalate has also been used. The base has been fractionally crystd by partial freezing and also from aq 80% EtOH then from absolute EtOH. It has been distd from zinc dust, under nitrogen. 

Attachment of a hot or cold stage to the ordinary microscope stage allows the specimen to be observed while the temperature is changed slowly, rapidly, or held constant somewhere other than ambient. This technique is used to determine melting and freezing points, but is especially useful for the study of polymorphs, the determination of eutectics, and the preparation of phase diagrams. 

If 0 lies below the freezing point of the solvent, the value of the dissociation constant will fall over the whole range of temperature. 

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,... 

Molal Freezing Point and Boiling Point Constants... 

When 13.66 g of lactic acid, C3H603j is mixed with 115 g of stearic acid, the mixture freezes at 62.7°C. The freezing point of pure stearic acid is 69.4°C. What is the freezing point constant of stearic acid ... 

Molal boiling point constant, 269,270t Molal freezing point constant, 269,270t Molality (m) A concentration unit defined as the number of moles of solute per kilogram of solvent, 259,261-262 Molar mass The mass of one mole of a substance, 55,68-68q alcohol, 591 alkane, 591... 

The most important case is the alteration of freezing-point with concentration at constant pressure, when ... 

At fairly high nitrous acid concentrations (0.1 m) and at moderate acidities (4 m) the blue color of N203 (Amax = 625 nm) is easily detected by eye. The overall equilibrium of Scheme 3-10 has been determined. A relatively recent determination of the equilibrium constant gave the value K = 3.0 x 10"3 m (Markovits et al., 1981). Accurate determinations of this constant are difficult, as N203 decomposes easily into NO and N02. Pure N203 is stable only as a pale blue solid or as an intensely blue liquid just above its freezing point (-100°C). The liquid starts to boil with decomposition above -40°C. 

The constant kf is called the freezing-point constant of the solvent it is different for each solvent and must be determined experimentally (Table 8.8). The effect is quite small for instance, for a 0.1 m C12H220n(aq) (sucrose) solution,... 

Take the freezing-point constant from Table 8.8. 

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