Freezing point raising

Fig. 34. Freezing point lowering AT (or raising, — AT) as a function of polymer concentration according to Eq. (26) and Eq. (27). (a) Normal polymer with no surface interaction contribution. K/kT s 1/m. Note saturation possible for > i. (b) Polymer with strong surface interaction contribution. K/kT 1/m. Note large initial depression slope and saturation possibility for x > i. (c) (K/kT + 1/m) (x — I). Quadratic term dominates. Note possibility of freezing point raising for x > b...

The particles in a solution lower the freezing point, raise the boiling point, and increase the osmotic pressure. In osmosis, solvent (water) passes through a semipermeable membrane from a solution with a lower osmotic pressure (lower solute concentration) to a solution with a higher osmotic pressure (higher solute concentration). Isotonic solutions have osmotic pressures equal to that of body fluids. 

The particles in a solution lower the freezing point, raise the boiling point, and increase the osmotic pressure. 

Liquid and Solid Acetylene. Both the Hquid and the soHd have the properties of a high explosive when initiated by detonators or by detonation of adjoining gaseous acetylene (85). At temperatures near the freezing point neither form is easily made to explode by heat, impact, or friction, but initiation becomes easier as the temperature of the Hquid is raised. Violent explosions result from exposure to mild thermal sources at temperatures approaching room temperature. 

Sucrose is often used as a decorative agent to impart a pleasing appearance to baked goods and confections (36). In jams and jeUies, sugar raises osmotic pressure and lowers water activity to prevent spoilage (18). Sucrose is a fermentation substrate for lactic acid in cultured buttermilk (40) and lowers the freezing point of ice cream and other frozen desserts to improve product mouthfeel and texture. 

As in the freezing-point method, the molecular weight is calculated from the weight of substance lequired to raise the boiling-point of too grams of solvent i°, and the result multiplied by a coefficient which depends upon the nature of the solvent. The following is a list of solvents commonly employed and their coefficients and boiling-points —... 

The freezing-point of water in contact with ether is lowered by 80,85 owing to the amount of the latter dissolved. If now a third substance (e.g., benzene) is added to the ether, which does not dissolve in the water, the freezing-point will be raised on account of the diminished solubility of the ether. The diminution of solubility of the ether is quite apparent to the eye if the liquids are contained in a graduated tube. 

The presence of a solute lowers the freezing point of a solvent if the solute is nonvolatile, the boiling point is also raised. The freezing-point depression can be used to calculate the molar mass of the solute. If the solute is an electrolyte, the extent of its dissociation, protonation, or deprotonation must also be taken into account. 

If gas-liquid and gas-solid separations are dependent on the saturation vapor pressure of the chemical component undergoing equilibration (a) What is the expected effect when the temperature of the system is raised (b) If the system is a gas-liquid system sketch what a plot of log VT vs. 1 IT would look like including when the T is below the freezing point of the stationary phase, (c) Why might it be better to sample the vapor phase above a solution as a sample to determine trace materials in the solution ... 

The freezing point of a solution of a nonvolatile solute is always lower than the pure solvent and the boiling point is always higher. It is the number of solute particles that determines the amount of the lowering of the freezing point and raising of the boiling point. 

Various alcohols and glycols can be used as antifreezes and are effective freeze point depressants for water. However, because glycols raise the boiling point of water while alcohols lower it, only glycol bases are recommended for use by engine manufacturers. 

Recent surveys have shown that over-concentration and under-concentration are common sources of cooling system problems. A minimum concentration of 33 1/3% is required to provide minimal corrosion protection. Maximum freeze protection is obtained at 68% by volume. Concentrations over 68% will adversely affect heat transfer, raise freezing point, and may cause inhibitors to precipitate from the coolant when the engine is operating. 

When a solute is present in water, the solute takes up space and decreases the number of liquid molecules at the liquid—solid interface. The space taken up by solute molecules decreases the probability of a water molecule adhering to the surface of ice and raising the overall freezing point of water. 

The lowering of the vapor pressure by a solute also brings about other changes the freezing point is lowered, and the boiling point is raised. The amount of... 

The physical stability of the casein micelle system is closely related to the degree of lactose crystallization from the unfrozen phase of the frozen concentrate. Crystallization of lactose from the unfrozen solution temporarily raises its freezing point, causing additional water to freeze, thus increasing the concentration and promoting destabilization of casein micelles. 

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