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РЕГИСТРАЦИЯ ЭКСКУРСИЯ

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Water

One of the most striking properties of water is its ability to dissolve many substances, forming aqueous solutions. Solutions are very important kinds of matter — important for industry and for life. The ocean is an aqueous solution that contains thousands of components: ions of the metals and non-metals, complex organic ions, many different organic substanccs. It was in this solution that the first living organisms developed, and it was from it that they obtained the ions and molcculcs needed for their growth and life. In the coursc of time organisms that were evolved could leave this aqueous environment, and move out onto the land and into the air. They achieved this ability by carrying the aqueous solution with them, as tissue fluid, blood plasma, and intracellular fluids containing the neccssary supply of ions and molccules.

The properties of solution have been extensively studied, and it has been found that they can be correlated in large part by some simple laws.

Water not only is the most widely used of all solvents, but also, of all liquids, it most nearly approaches being the "universal solvent". Every substancc is probably soluble in water to some extent, although in many cases the solubility is so small that it is almost impcrscptiblc. Thus, a saturated solution of barium sulphate contains less than a quarter of a milligram of solute per litre, and the solubility of silicon dioxide (quartz)—is even smaller than this. Yet, water that is allowed to remain for a long time in a quartz vessel must eventually become saturated with quartz; a saturated solution of this substancc is so extremely dilute, however, that many litres of it would have to be evaporated to dryness in order to yield a visible residue. Such substanccs as barium sulphate, silver chloride, quartz, glass, mercury, and cellulose are usually considered as "insoluble" in water, but this term, it must be remembered, is merely a relative one, and it would be more accuratc to say that their solubility is exceedingly small.


19.01.2015; 01:28
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