Freezing from

The compound is very soluble in most organic solvents. In order to get a high recovery, it is necessary to complete the crystallization in the deep freeze. From aqueous ethanol the aldehyde crystallized in high yield as the hemihydrate, m.p. 95°. 

Equation (8.26) relates the melting temperature, T, of an ideal solution to the mole fraction,, v of the (pure) component that freezes from solution. It can be integrated by separating variables and setting the integration limits between T, the melting temperature where the mole fraction is. y, and 7, the melting temperature of the pure component, /, where. v, = 1. The result is... 

Figure 8. Photomicrographs of frog erythrocytes in serum during the course of slow freezing from -1.5 °C to -10 °C. Note that the cells are confined to the channels of unfrozen solution between the ice crystals (I), that the channels decrease in diameter with decreasing temperature, and that the cells shrink. (From Rapatz el al., 1966.)...

FIGURE 26.11 Frictional properties of ice when slight amounts of different salts are added to the water before freezing. (From Roberts, A.D. and Lane, J.D., J. Phys. D, 16, 275, 1983.)... 

When a crystal freezes from the melt, it tends to reject impurities. If zone - refining is applied to such a crystal, the resulting single crystal can be purer than the originaL If we make more than one pass, we can approach a high degree of purity. Such a procedure is called "zone- refining". 

If water acted like benzene, lakes would freeze from the bottom up and become solid ice. In a benzene world, fish could not survive in colder climates. Icebergs would be at the bottom of the sea, and the Titanic might still be afloat. The world as we know it would be topsyturvy if water behaved like benzene. That leads to the question Why doesn t it ... 

The nature of the bonds between an oxygen atom and two atoms of hydrogen has an enormous impact on how our planet works. Because of the highly polar covalent bond, salt dissolves in water, which enabled our ancestors to preserve meat. It also produces the hydrogen bonds that make our lakes freeze from the top down, per-... 

When frozen from both surfaces a = half thickness for freezing from one surface. 

Figure 3.6 Experimental heat transfer coefficients in fluidized bed freezing. From Vazquez and Calvelo (1983a), by permission of the Institute of Food Technologists, USA.

If cooling occurred at the bottom of a pond instead of at the surface, would a lake freeze from the bottom up Explain. 

There is some form of hydrogen disorder in nearly all polymorphs, just as in ice(Ih). However the rhombohedral ice(II) is an exception. Its protons are ordered. As was suggested by Whalley (1967), this may have profound significance. Were ice(II) proton-disordered, it would have a higher entropy. A possible consequence would be that this polymorph would become thermodynamically stable under conditions that might arise on Earth. As ice(II) has a density 1.2 g cm-3, it would then accumulate at the bottom of lakes or seas, so that Earth s waters would freeze from the depths upwards. Life, as we know it, could hardly have developed, or survived, in such circumstances. 

Latent heat of freezing from a dilute sodium chloride solution assumed to be same as for pure water... 

The relationship between melting temperature T and mole fraction when a pure solid freezes from an ideal solution is given by equation (11.85)... 

It is instructive to compare the changes that occur when liquids with compositions given by points a, f, and j are cooled. Cooling along line abcde reverses the process described above. That is, ice freezes from the solution at point b. With continued cooling, more ice forms and the liquid follows line bp. At point c, the ice that has collected reacts with the liquid solution (composition given by p) to form hydrate... 

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