Seawater freezing point

The freezing point, temperature of maximum density, osmotic pressure and specific heat for seawater of various salinities are given in Table 21.23. 

Assuming that each ion acts independently of all the others and that seawater has a density of 1.026 g/mL, calculate the freezing point and osmotic pressure of seawater. The actual freezing point of seawater is - 1.96 ° C. What conclusion can you reach about your assumptions Take this into account and recalculate the osmotic pressure of seawater. 

Thermal expansion Temperature of maximum density decreases with increasing salinity for pure water it is at 4°C Fresh water and dilute seawater have their maximum density at temperatures above the freezing point this property plays an important part in controlling temperature distribution and vertical circulation in iakes... 

The temperature at which seawater reaches its maximum density also decreases with increasing salinity. Most seawater in the ocean has a salinity between 33% and 37%. At salinities greater than 26%, the freezing point of seawater is higher than the temperature at which it reaches its maximum density. Thus, seawater never undergoes the anomalous density behavior of pure water. Instead, sea ice floats because it is mostly pure water (some pockets of brine are often occluded into the crystal structure). 

Each kilogram of seawater contains roughly 35 g of dissolved salts. Assuming that all these salts are sodium chloride, what is the freezing point of seawater ... 

Because this value is merely the freezing point depression, you must subtract it from the freezing point of the pure solute to get 0°C-2.23°C = -2.23°C, the freezing point of seawater. 

Alternatively, potable water can be extracted from seawater by freezing salts, which depress the freezing point of water, remain in the liquid phase. Generally, though, it is more practical to remove the relatively small amount of solutes (typically, 0.02% for river water) from the great excess of water, rather than vice versa. Seawater is an exceptional case, with about 3.5% dissolved solids. Water softening is concerned primarily with removal of Ca2+ and Mg2+, but for some purposes removal of all dissolved solids (deionization or demineralization) is necessary. 

The temperature of the present ocean averages 4°C, with the surface waters somewhat warmer. Whereas the freezing point of water is 0°C, the freezing point of seawater is - 1.8°C. Seawater solidifies almost completely at -21°C. The temperature of the primitive ocean is not known, but it can be said that the instability of various organic compounds and polymers makes a compelling argument that life could not have arisen in... 

Assuming that seawater is a 3.5 mass % solution of NaCl and that its density is 1.00 g/mL, calculate both its boiling point and its freezing point in °C. 

Table A.5 is the output file for salts in the 4.5- to 5.0-km layer, where the system pressure is 484.5 bars (102 bars km-1 x 4.75 km). The temperature of 268.28 K is the freezing point depression for this particular composition and pressure at 268.27 K, ice forms. The pH of this system is 8.02. The number of independent components is seven. This example deals with lithostatic pressures on solutions dispersed in a regolith, which is fundamentally different from the previous examples (Tables A.2-A.4) that dealt with seawaters.

Figure 2 The temperature of maximum density (—) and freezing point (- -) of seawater as a function of dissolved salt content (Adapted from Tchernia, 1980. )...

Miyake Y. (1939) Chemical studies of the western Pacific Ocean 111. Freezing point, osmotic pressure, boiling point, and vapor pressure of seawater. Chem. Soc. Japan Bull. 14, 58-62. 

The number of moles of the major dissolved species in a 1.000-L sample of seawater are as follows. Estimate the freezing point of the seawater, assuming K = 1.86 K kg mol for water. 

The seawater should freeze at approximately -2°C. Nonideal solution effects make the actual freezing point slightly higher than this. 

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