Aqueous freezing points

Free Energy Perturbation Monte Carlo Simulations of Salt Influences on Aqueous Freezing Point Depression... 

Fig. 2. Freezing points of aqueous glycol solutions. A, ethylene glycol B, diethylene glycol C, triethylene glycol and D, tetraethylene glycol. Ethylene glycols...

Freeze Point Depression. The slight heat-transfer penalty incurred when an antifreeze is added to the aqueous heat-transfer fluid is necessitated by the need for increased operating temperature range in most internal combustion engines. Because most parts of the world achieve temperatures below freezing during some time of the year, an antifreeze fluid is required to keep equipment operational in these subfreezing temperatures. 

Potassium hydroxide is the principal electrolyte of choice for the above batteries because of its compatibiUty with the various electrodes, good conductivity, and low freezing point temperature. Potassium hydroxide is a white crystalline substance having a mol wt = 56.10 density = 2.044 g/mL, and mp = 360° C (see Potassium compounds). It is hygroscopic and very soluble in water. The most conductive aqueous solution at 25 °C is at 27% KOH, but the conductivity characteristics are relatively flat over a broad range of concentrations. 

Commercial appHcations of calcium chloride and its hydrates exploit one or more of its properties with regard to aqueous solubiUty, hygroscopic nature, the heat gained or lost when one hydrated phase changes to another, and the depressed freezing point of the eutectic solution at a composition of about 30% by weight calcium chloride. 

Figure 11-16. Freezing points of aqueous solutions of ethylene and propylene glycol. (Used by permission 1977ASHRAEHandbook, l-P Ed., Fundamentals, 1979 ASHRAE Handbook and Product Directory, 1979,1980 2"= printing, American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc. All rights reserved.)...

The internal structure of a liquid at a temperature near its freezing point has been discussed in Sec. 24. Each molecule vibrates in a little cage or cell, whose boundaries are provided by the adjacent molecules, as in Fig. 20, and likewise for each solute particle in solution in a solvent near its freezing point. It is clear that the question of the hydration of ions no longer arises in its original form. In aqueous solution an atomic ion will never be in contact with less than three or four water molecules, which in turn will be in contact with other water molecules, and so on. There is an electrostatic attraction, not only between the ion and the molecular dipoles in immediate contact with it, but also between the ion and molecular dipoles that are not in contact with it. For solvent dipoles that are in contact with a small doubly charged ion, such as Ca++,... 

The freezing points of electrolyte solutions, like their vapor pressures, are lower than those of nonelectrolytes at the same concentration. Sodium chloride and calcium chloride are used to lower the melting point of ice on highways their aqueous solutions can have freezing points as low as —21 and — 55°C, respectively. 

What is the freezing point of vinegar, which is an aqueous solution of 5.00% acetic acid, HC2H3O2, by mass (d = 1.006 g/cm3) ... 

The ionisation may be attributed to the great tendency of the free hydrogen ions H+ to combine with water molecules to form hydroxonium ions. Hydrochloric and nitric acids are almost completely dissociated in aqueous solution in accordance with the above equations this is readily demonstrated by freezing-point measurements and by other methods. 

A similar method was used in connexion with the lowering of vapour pressure in 130. It is evident that, since the factor i was introduced in the same connexion in both investigations, the values of i obtained by both methods, viz., by measurements of vapour pressure and of freezing-point, are necessarily the same, and their agreement is therefore independent of any theory which we may adopt to explain the anomalous behaviour of aqueous salt solutions. 

J. B. Goebel (Zeitschr. physik. Chem., 53, 213, 1905 54, 314, 1906 71, 652, 1910) has found an empirical equation for the depression of freezing-point in aqueous solutions of total molecular concentration n ... 

Freezing point methods are often applied to the measurement of activities of electrolytes in dilute aqueous solution because the freezing point lowering, 6= T — T, can be determined with high accuracy, and the solute does not dissolve in the solid to any appreciable extent. Equations can be derivedgg relating a to 9 instead of T and T. The detailed expressions can be found in the literature.16... 

Determine the freezing point of a 0.10 mol-kg aqueous solution of a weak electrolyte that is 7.5% dissociated into two ions. 

Colligative properties can be sources of insight into not only the properties of solutions, but also the properties of the solute. For example, acetic acid, CH.COOH, behaves differently in two different solvents, (a) The freezing point of a 5.00% by mass aqueous acetic acid solution is — l.72°C. What is the molar mass of the solute Explain any discrepancy between the experimental and the expected molar mass, (b) The freezing-point depression associated with a 5.00% by mass solution of acetic acid in benzene is 2.32°C. Whar is the experimental molar mass of the solute in benzene What can you conclude about the nature of acetic acid in benzene ... 

C12-0069. List the following aqueous solutions in order of decreasing freezing point, and explain your listing 0.30 M NaCl, 0.75 M NH3,0.25 M MgCl2,0.25 M NH3. ... 

C12-0074. The freezing point of an aqueous solution containing pantothenic acid... 

C12-0097. When an aqueous solution cools to low temperature, part of the water freezes as pure ice. What happens to the freezing point of the remaining solution when this occurs A glass of wine placed in a freezer at -10 C for a very long time forms some ice crystals but does not completely freeze. Compute the molality of ethanol in the remaining liquid phase. 

Mixtures of aqueous emulsions of oil can be more effectively transported through pipelines if certain antifreeze formulations are added to the system. Stable oil-in-water emulsions for pipeline transmission by using 0.05% to 4% ethoxylated alkylphenol as an emulgator and a freezing-point depressant for water enable pipeline transmission at temperatures below the freezing point of water [736]. 

Similarly, concepts of solvation must be employed in the measurement of equilibrium quantities to explain some anomalies, primarily the salting-out effect. Addition of an electrolyte to an aqueous solution of a non-electrolyte results in transfer of part of the water to the hydration sheath of the ion, decreasing the amount of free solvent, and the solubility of the nonelectrolyte decreases. This effect depends, however, on the electrolyte selected. In addition, the activity coefficient values (obtained, for example, by measuring the freezing point) can indicate the magnitude of hydration numbers. Exchange of the open structure of pure water for the more compact structure of the hydration sheath is the cause of lower compressibility of the electrolyte solution compared to pure water and of lower apparent volumes of the ions in solution in comparison with their effective volumes in the crystals. Again, this method yields the overall hydration number. 

Industrial liquid urea is known as Adblue . This industrial liquid [chemical formula (NH2)2CO] is an aqueous solution of 32.5% wt urea solution (see Figure 7.14). Adblue is corrosive and requires stable materials for the components like tank, pipes, injector, etc. Moreover, this solution is not suitable for year-round use in the Northern countries the freezing point is at —11°C. Urea hydrolysis requires at least 180°C. 

Procedure Allelopathic aqueous leachate is prepared by soaking dried leaves (lg/100 mL or 1% w/v) in distilled water for 3 h. This leachate is filtered through Whatman paper (No. 4) and then through a sterile Millipore membrane (0.45 mm). Then, it is poured in Petri dishes and mixed with agar (2%) for a final aqueous leachate concentration of 0.5%. The volume will depend on the size of the Petri dish, 3 mL of leachate plus 3 mL of agar are enough for a 6 cm Petri dish. Osmotic potential of the leachate is measured with a freezing-point osmometer (Osmette A, Precision System Inc.). 

---