The UN Resolution introduces an annual World Daywater, which is celebrated in different countries on March 22. On this day, activities are carried out whose purpose is to preserve and develop water resources that are in rivers, lakes, canals, storages, seas and oceans, in underground sources in the form of soil moisture, polar and mountain ice or vapor in the atmosphere. All resources include underground and surface sources and can be used or used for human needs. The total volume of them (in the liquid, gaseous or solid state) on Earth is 1390 million cubic meters, and only less than 3% of all resources fall to fresh stocks.
In the oceans and seas is the largestthe amount of water (about 98%) of all surface sources. Its chemistry varies depending on the terrain and season. Sea water contains much more dissolved ions than any kind of fresh water. Also sharply differs by the ratio of the substances dissolved in it. For example, in seas and oceans, there are approximately 2.8 times more bicarbonates than in rivers, but their molar fraction with respect to all dissolved ions is much lower (0.14%) than in river sources (48%). This is due to the different residence times of the solutes. Sodium and chlorine ions are in a dissolved state, while calcium precipitates as a carbonate. According to the content in a kilogram of sea water, the most common ions are:
- chlorine (0.546 mol);
- sodium (0.469 mol);
- magnesium (0.0528 mol);
- sulfate (0.0282 mol);
- calcium (0.0103 mol);
- potassium (0.0102 moles).
One of the most important indicatorscharacterized by sea water - it's salinity. It is measured in ppm (‰) and is different for all seas and oceans. The average salinity is 35 ‰, that is, in 1 liter, 35 g of salts are in the dissolved state, mainly sodium chloride. With an average salinity, the elementary composition of water is as follows:
- oxygen 85.84%;
- hydrogen 10.82%;
- chlorine 1.94%;
- magnesium 1.1292%;
- sodium 1.08%;
- sulfur 0.091%;
- calcium 0.04%;
- potassium 0,04%;
- bromine 0.0067%;
- carbon 0.0028%.
Sea water on the surface at 25 ° C has an averagethe density of 1,025 g / cm3 is more than the pure one, whose density at 25 ° C is equal to 1.003 g / cm3. Density is a physical quantity that has a direct dependence on the salt concentration and is inversely related to temperature. The more dissolved the salts, the greater the density. The lower the temperature of sea water, the greater the density. Temperature at the highest density minus 3.52C for marine and plus 3.98C for clean. But these quantities vary not only from source to source, but also depend on the depth at which they are measured. At great depths, the density can reach a value of 1,050 g / cm3 and even higher. The change in the qualitative and quantitative composition is also well traced in the pH value, which varies within 7.5-8.4 (the medium is slightly alkaline) and is caused by the nature of the dissolved ions and their concentration. The pH of the surface is higher than at the depth. A neutral and slightly acidic medium may be a medium of freshened areas. The highest pH value (the lowest concentration of hydrogen ions) is always observed at the sea surface.
The freezing point of sea water decreases withincrease in salinity (concentration of dissolved salts). At an average salinity, it freezes at a temperature close to minus 2C. In 2010, the lowest temperature in the stream under the Antarctic glacier was recorded in history, when it was measured minus 2.6C. There are other characteristics that show the difference between sources, as well as their variability depending on other parameters. For example, the speed of sound at 0С. It passes through the marine environment in 1 second 1450 m, and through a clean one - 1407 m. Sea water at 25C has a dynamic viscosity of 9.02 mPO. For a pure medium, this same characteristic at the same temperature equals 8.09 millipoise.
Sea water is not used for drinking because ofhigh concentration of mineral salts. When you use it, you need to drink a lot more pure liquid to remove all the salt that came with it from the body. Therefore, only fresh water is consumed, in which not more than 0.001 g / cm3 of salt is dissolved. Because of its deficiency, plants are built and special methods are used to reduce the concentration of salts. These include freezing, distillation, electrolysis, ion exchange, reverse osmosis, separation (hydrodynamic separation). For example, in Kazakhstan, the city of Aktau (formerly known as Shevchenko) was built in 1972 and the world's only nuclear desalination plant operated for almost 30 years.
