Freezing-point depression applications

Special formulations have been developed for cementing operations in arctic regions or for deep water applications [206,208,256,720,739,1792]. In low-temperature formations, wherein the cement is subjected to freeze-thaw cycling, freezing-point depressants must be added. Salts may serve as such, but traditional organic freezing-point depressants, such as ethylene glycol, also may be added [1022-1024]. 

The extensive application of N204 in pure form to rocketry is a fairly recent development however, its use as a stabilizer and freezing point depressant for HN03 dates back more than 15 years. Mixtures of HN03, N204, and small amounts of water and HF are referred to as inhibited red fuming nitric acid (IRFNA) or without the HF (a corrosion inhibitor) as merely red fuming nitric acid (RFNA). 

Due to a cancellation of errors, the equation (without modification) is applicable for aqueous ethylene glycol concentrations to about 0.40 mole fraction (typically for system operation to 233 K). A comparison of results from Hammerschmidt s equation, as well as the prediction by the freezing point depression of water for methanol inhibition is summarized in Table 4.6. 

The up to now most frequently used techniques as, for example, vapour pressure osmometry (VPO) or freezing point depression (with its limitation regarding the solvent dependent measuring temperature) are based upon the colligative properties of the system the classical absolute light-scattering and ultracentrifugation techniques are only occasionally and approximately applicable with respect to the determination of CMC values. Evaluation of critical micelle concentrations which are based on these latter methods suffer considerably from the insensitivity of these techniques if measurements below the CMC, i.e., below about 10-3 mol dm-3, are carried out. More sensitive methods will be discussed below. 

Kf is a function of properties of the liquid enclosed in the pores (constant). The tf term is tentatively proposed to be identical to the thickness of a surface layer of nonfteezing water, which effectively reduces the actual pore radius frrom rp to rp - tf. The pore size distribution of amoiphous silica determined independently by NMR and nitrogen adsorption agreed well. However, the application of this method to microporous materials (rp < 10 A) may be limited. By establishing a correlation between the freezing point depression AT and the pore size rp of mesoporous mat ials, a new method for the determination of pore size distributions was created (81). 

Suzuki, M. Ito, K. Fushimi, C. Kondo, T. Application of freezing point depression to drug interaction studies. I. A study of 1 1 Plus 1 2 complexes between barbiturate and a-cyclodextrin using the freezing point depression method. Chem. Pharm. Bull. 1993, 41 (8), 1444—1447. 

The four colligative properties that are of importance are 1) the vapor pressure lowering 2) the elevation of boiling point 3) the freezing-point depression and 4) the osmotic pressure. An attempt is made below to describe qualitatively and quantitatively each colligative property of solutions, with an emphasis on their interrelationship and their application later in measurement and adjustment of the tonicity of solutions, with particular reference to parenteral formulations. Although theoretical derivations based on thermodynamics can be used to show how each of the colligative properties of solution arises and relate to each other, textbooks on physical chemistry for theoretical derivations are recommended. 

Fructose contributes useful physical and functional attributes in food and beverage applications, including sweetness, flavor enhancement, humectancy, freezing-point depression, and osmotic stability.144... 

A practical application of the freezing-point depression is described in the following example. 

The toxicity of antifreeze and deicing fluids is predominantly a function of the main component, the freezing point depressant. For ethylene glycol-based fluids, the toxicity is well-defined, as the toxicity of ethylene glycol has been studied extensively because of its wide usage in varied applications (16). 

Practical applications that take advantage of freezing point depression of solutions by solutes include the following ... 

Another application of a power series in physical chemistry is in the discussion of colligative properties (freezing-point depression, boiling-point elevation, and osmotic pressure). If is the mole fraction of solvent, AyapHm is the molar heat of vaporization of the solvent, Tq is the pure solvent s boiling temperature, and T is the solution s boiling temperature, it is shown in physical chemistry textbooks that... 

You have encountered practical applications of freezing point depression if you have added antifreeze—a solution of ethylene glycol in water—to your car s radiator or have seen airplane de-icers used before takeoff. Also, roads are salted with NaCl and CaCl2 in winter to lower the freezing point of water, causing road ice to melt. 

A common application of freezing-point depression and boiling-point elevation experiments is to provide a means to calculate the molar mass of a nonvolatile solute. What data are needed to calculate the molar mass of a nonvolatile solute Explain how you would manipulate these data to calculate the molar mass of the nonvolatile solute. 

FREEZING POINT DEPRESSIONS. The application of the fundamental laws of thermodynamics to the freezing point depressions, on the assumption that the solid species coming out of solution is the pure component, leads to expressions for the activity coefficients along the freezing point curve... 

For example, in an aqueous non-electrolyte solution with a mole fraction of Xb = 0.01, ATsi is about -1 K. An example from everyday life is shown in Experiment 12.10. A prime example of an application of freezing-point depression is, however, the melting effect of road salt. 

A characteristic of such systems is that the freezing line is curved downwards, that is, mixtures of the two components have a lower freezing point than either component. This is known as freezing point depression. A common application of this phenomenon is in deicing. By mixing ice with a nonvolatile solute, the ice-solute mixture becomes liquid even at temperatures where pure water would be solid. 

The freezing-point depression caused by solutes has useful applications it is why antifreeze works in car cooling systems, and why calcium chloride (CaCl2) promotes the melting of ice on roads during winter. 

A practical application of freezing-point depression and boiling-point elevation is described in Example 9.8. 

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