Sodium chloride freezing-point depression

Antifreezing agents for cement consist mainly of salts such as calcium chloride, magnesium chloride, sodium chloride, and soda. Calcium chloride is highly corrosive and very restricted in use. Some salts, especially potassium chloride, will affect the curing time of cement. The latter chemical is in fact used to increase the pot life of cement. Likewise, alcohol freezing-point depressants, such as ethylene glycol, can be also included in the composition [1022]. 

We must appreciate, however, that no chemical reaction occurs between the salt and the water more or less, any ionic salt, when put on ice, will therefore cause it to melt. The chemical identity of the salt is irrelevant - it need not be sodium chloride at all. What matters is the amount of the salt added to the ice, which relates eventually to the mole fraction of salt. So, what is the magnitude of the freezing-point depression ... 

TABLE 8.2. Sodium Chloride Equivalents (E) and Freezing Point Depression (ATI" ") Values of Selected Compounds. 

Step 3 Since 0.9% sodium chloride has a freezing point depression of 0.52, one can calculate the percentage concentration of sodium chloride required to lower the difference in freezing points, i.e., the value obtained in Step 2, ATf, by the method of proportion. The calculations involved in this method are explained best by following examples. 

The filtrate, obtained after the crystals of bis-(4-iminopentane-2-ono) copper (II) were filtered off, was evaporated under reduced pressure. The residue was extracted with water, the extracts were filtered, and the filtrate was treated with sodium hydroxide and p-toluenesulfonyl chloride (18). In this way, about 30% of the 1,3-propanediamine was accounted for as the crude ditosylate (identity confirmed by lack of freezing-point depression with authentic sample), but only a trace of diamine could be detected in the distillate. 

In Equation 4.21, the activity of pure water (a) is unity and the activity of the water with the inhibitor (a ) is the product of the water concentration (xw) and the activity coefficient (xw). The water concentration is known and the activity coefficient is easily obtained from colligative properties for the inhibitor, such as the freezing point depression. For instance the activity of water in aqueous sodium chloride solutions may be obtained from Robinson and Stokes (1959, p. 476) or from any of several handbooks of chemistry and physics. 

Various salts can cause freezing point depressions. These depressions are the results of the ions colligative properties within solution. A significant freezing point depression is created not by any particular type of material, but rather by the number of particles you have in solution. The effects can be enhanced by achieving a supersaturation of material. For example, if you mix ice with a salt such as NaCl, you will end up with two particles within solution (Na+ + Cl ) (the temperature of ice water supersaturated with sodium chloride (23% by weight) is -20.67°C). If you place a salt such as CaCl2- H20 into ice, you will end up with three particles within the solution (Ca+ + 20 ) [the temperature of ice water... 

The collected urine is centrifuged to remove solid debris and analyzed by standard methods for sodium, potassium and chloride (Durst and Siggard-Andersen, 1999, Scott et al. 1999). Osmolality is also measured with an osmometer (the freezing point depression type of instrument is recommended (Scott et al. 1999). 

Table 1 Freezing point depressions (7/° °), Ljso values and sodium chloride equivalents (E) for drugs and excipients for adjusting their solutions to isotonicity (Continued)...

The sodium chloride equivalent (E) is the amount of sodium chloride equivalent to 1 g of the drug in exerting the same osmotic effect. The E value for a new drug can be calculated from its Li o value or from the freezing-point depression as shown below. 

By definition, E gram of sodium chloride MW = 58.45 and L so = 3.4) in 1 L will have similar freezing-point depression as shown below ... 

Aqueous sodium chloride solurion (% w/v) Freezing point depression (°C)... 

Some types of injections must be isotonic with blood serum. This applies particularly to large volume intravenous infusions if at all possible hypotonic solutions cause lysis of red blood corpuscles and thus must not be used for this purpose. Conversely, hypertonic solutions can be employed these induce shrinkage, but not lysis, of red cells, which recover their shape later. Intraspinal injections must also be isotonic to reduce pain at the site of injection so should intramuscular and subcutaneous injections. Adjustment to isotonicity can be determined from either the depression of freezing point or from sodium chloride equivalents. The depression of the freezing point depends on the... 

Sodium metal is produced by the electrolysis of molten rock salt (impure sodium chloride) and calcium chloride. Calcium chloride lowers the melting point of sodium chloride (recall freezing point depression), increasing the energy efficiency of the process. 

Osmolality determinations are usually carried out using a cryoscopic osmometer, which is calibrated with deionized water and solutions of sodium chloride of known concentration. Using this technique, the sodium chloride equivalents and freezing point depressions for more than 500 substances have been determined and reported in a series of papers by Hammerlund and co-workers (e.g., see Hammerlund 1981). Figure 6.18 shows the osmolality of mannitol-water solutions. 

It is important to remember that the values just calculated are only expected values. As stated earlier, a 0.1 m solution of sodium chloride lowers the freezing point nearly twice as much as a 0.1 m solution of sucrose. The actual values of the coUigative properties for all strong electrolytes are a/most what would be expected based on the number of particles they produce in solution. Some specific examples are given in Figure 2.6. The freezing-point depression of a compound that produces two ions per formula unit is almost twice that of a nonelectrolytic solution. The freezing-point depression of a compound that produces three ions per formula unit is almost three times that of a nonelectrolytic solution. 

Media formulations do not generally specify the osmotic pressure instead, the number of dissolved particles is given as osmolarity or osmolality. Osmolality is the number of moles of particles per kilogram of solution whereas osmolarity is the number of moles per liter of solution. One mole of particles is an osmole, abbreviated as Osm. Animal cell culture media have an osmolality of 280 to 320 mOsm kg to conform to the osmolality of serum (290 mOsm kg ). Osmolality is not easily calculated especially when a medium has many components and the degree of dissociation is not known. In such cases, osmolality is estimated from measurements of freezing point depression and other colligative properties (i.e., those dependent on the concentration of dissolved particles). In cell culture media, sodium chloride is used for adjusting osmolality to the requisite value. 

Just as the freezing point depression of a solution containing an electrolyte solute is greater than that of a solution containing the same concentration of a nonelectrolyte solute, so the vapor pressure lowering is greater (for the same reasons). The vapor pressure for a sodium chloride solution, for example, is lowered about twice as much as it is for a nonelectrolyte solution of the same concentration. To calculate the vapor pressure of a solution containing an ionic solute, we need to account for the dissociation of the solute when we calculate the mole fraction of the solvent, as shown in Example 12.12. 

Table 8.Q shows the experimental/data for the freezing-point depression of sodium chloride in water at 1 atm [20]. Using this table,... 

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