Ethanol freezing-point depression

Like brines, alcohols were readily available and widely used as antifreeze Hquids in the early 1900s. Both methanol and ethanol offer exceUent heat transfer and efficient freeze point depression. However, the alcohols have the distinct disadvantage of their low boiling points. During the summer months when the engines operate hot, significant amounts of the alcohols are lost because of evaporation. These evaporative losses result in cosdy make-up requirements. Additionally, the alcohols have very low flash points and potentially flammable vapors. These safety concerns have, particularly in recent years, caused the use of alcohols to be completely discontinued for most heat-transfer systems. 

The freezing-point depression constant of pure H2SO4 is 6.12 K kg mol . When 2.3 g of ethanol (C2H5OH) is dissolved in 1.00 kg of pure sulfuric acid, the freezing point of the solution is 0.92 K lower than the freezing point of pure sulfuric acid. Determine how many particles are formed as 1 molecule of ethanol goes into solution in sulfuric acid. 

An important clinical difference between the vapor pressure technique and the freezing point depression osmometer is the failure of the former to include in its measurement of total osmolality any volatile solutes present in the serum. Substances such as ethanol, methanol, and iso-propanol are volatile, and thus escape from the solution and increase the vapor pressure instead of lowering the vapor pressure of the solvent (water). This makes use of vapor pressure osmometers impractical for identifying osmolal gaps in acid-base disturbances (see Chapter 46). Thus use of this type of osmometer cannot be recommended for most clinical laboratories. 

The dotted line with the open symbols on the right side of the diagram is the freezing curve of ethanol in tire mixture. As one passes downward through this curve, solid ethanol precipitates from the solution. Note that the temperature at which ethanol begins to freeze decreases as the amount of water in the solution increases. Therefore, we see that the addition of impurities decreases the freezing temperature of a substance. This phenomena is known as freezing point depression. 

Pentaethoxyuranium is a dark-brown, mobile liquid with a density of 1.71 g/cm3 at 25°.2 The liquid boils at 123° at 0.001 torr and is thermally stable below 170°. The compound is readily hydrolyzed and is oxidized by dry oxygen (in the presence of excess NaOC2Hs) to hexaethoxyuranium.2 Pentaethoxyuranium has a dimeric structure at room temperature as determined by freezing-point depression measurements in benzene.2 It is miscible with ethanol, diethyl ether, benzene, petroleum ether, ethyl acetate, carbon tetrachloride, chloroform, carbon disulfide, pyridine, dioxane, and nitrobenzene. The proton magnetic... 

The freezing point depression of solutions of ethanol in water is given by... 

Challenge A 0.045m solution (consisting of a nonvolatile, nonelectrolyte solute) is experimentally found to have a freezing point depression of 0.08°C. What is the freezing point depression constant (/Cf). Which is most likely to be the solvent water, ethanol, or chloroform ... 

The vapor pressure depression method has the advantage of smaller sample size. However, it is not as precise as the freezing point method and cannot measure the contribution of volatile solutes such as ethanol. This method is not used as widely as the freezing point depression method in clinical laboratories. 

The automotive windscreen de-icer and screenwash market is a significant user of methanol, ethanol and isopropanol. The alcohol present acts as a freezing point depressant. Western Europe uses 80-100ktpa of these alcohols. 

Acetic and benzoic anhydrides give four fold freezing point depressions in sulfuric acid (134) but because of their instability (221) one cannot be sure whether they are completely protonated. Phthalic and succinic anhydrides are only partially protonated in this medium (134,221). However, against ethanol as a hydrogen-bond donor acetic anhydride is more basic than ethyl acetate (64). 

In higher doses, ethanol and barbiturates also depress the thermoregulatory center (Bl), thereby permitting cooling of the body to the point of death, given a sufficiently low ambient temperature (freezing to death in drunkenness). 

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