Salt water
As salt water one will solution of salts in water , respectively. As a rule, it is understood to mean a saline solution of at least 1% ( mass fraction ). In the Anglo-Saxon region, a salt content above 1.8% is assumed. Water with a lower salt content (e.g. in the area of river mouths into the sea) is called brackish water , water below 0.1% salt content is fresh water . On earth, the sea water in the oceans is the most abundant salt water and at the same time the largest amount of water. The average salt content of the oceans is 3.5%. The highest salt concentration (44.2%) is found in the (hypersaline) water of Lake Don Juan , but there is v. a. Calcium chloride and relatively little sodium chloride (2.9% mass fraction) dissolved.
properties
Due to the salt content of around 3.5%, the density of sea water is a good 3% higher than fresh water at the same temperature, around 1.025 kg / l at 25 ° C. This increase in density increases the lift force per penetration volume, so that, for. B. Ships submerge less deeply in salt water - or can load more - than in fresh water. Due to equilibrium, the total buoyancy force must also remain constant for a ship with constant weight force, so the ship must sink deeper in order to maintain the buoyancy force constant. Fresh water from an emptying river tends to flow into the sea in a near-surface layer before it is mixed in by eddies and waves, even if it is much colder than seawater. In the Strait of Gibraltar there are superimposed opposing currents of the sea water: Atlantic water with less salt flows (depending on the surface gradient) into the more evaporation-intensive Mediterranean, and at depth the Mediterranean water, which is heavier due to the higher salt content, flows out into the Atlantic.
A saturated saline solution has a freezing point of −21 ° C, a boiling point of 108 ° C and contains 356 g sodium chloride per liter at 0 ° C (359 g / l at 25 ° C). Compared to pure water, salt water up to a salt concentration of 190 g per liter has a specific heat capacity up to 0.13% lower , with a higher salt content up to 1.8% higher heat capacity.
If ice is to be used for cooling, low temperatures can be generated by adding different salts (see common cold mixtures ).
Compared to pure water, salt water has an electrical conductivity that is several orders of magnitude higher .
Habitats
Habitats that are determined by salt water are also called saline (from Latin sal 'salt') or haline (from ancient Greek háls 'salt' ) biotopes . Life in salt water requires special adaptations from organisms that have conquered habitats in the sea or in salt lakes in the course of evolution . B. salt glands or increased efficiency of the kidneys , Malpighian vessels or protonephridia for excretion / excretion. Plants that are specially adapted to saline biotopes are called halophytes .
Depending on the salinity, a distinction is made between mixohaline waters with a salinity below that of seawater (e.g. brackish water in estuaries or the Baltic Sea), global seawater itself with a salinity of 3.47% (called euhalin ) and waters with an even higher salinity (called hyperhalin ) (e.g. Mediterranean, Dead Sea).
Overview
The following table gives an overview of the usability and designation of salt water of different concentrations:
Type of water according to origin or type of use |
Salinity Salt concentration in ppmw |
particularities | |
|---|---|---|---|
| From | to | ||
| Rainwater | 0 | ? | Freezing point 0.0 ° C, carbonate ions from dissolved CO 2 , traces of salt near the sea or other sources of salt dust |
| Freshwater | 0 | 1,000 | Freezing point 0.0 ° C |
| Brackish water | 1,000 | 10,000 | Freezing point 0.0 ° C to −0.6 ° C |
| Brackish water (Anglo-Saxon) | 500 | 30,000 | Freezing point 0.0 ° C to −1.75 ° C |
| Mixohaline water | 1,000 | 30,000 | |
| Sea water, euhaline water | 34,700 | Freezing point -1.9 ° C | |
| Salt water, hyperhaline water | 30,000 | Freezing point below −1.75 ° C | |
| Don Juan Lake | 442,000 | Freezing point −51.8 ° C, as mainly calcium chloride | |
| Dead Sea | 280,000 | Freezing point −21 ° C | |
| Saturated saline solution | 356,000 | Freezing point −21 ° C; Boiling point 108 ° C | |
| Drinking water , edible for humans | 0 | 3,000 | |
| Drinking water recommended for people | 0 | 200 | |
| Isotonic saline solution | 9,000 | ||
| Irrigation water (with optimal soil and drainage conditions) |
0 | 750 | no risk of salination |
| 750 | 1,500 | low yields in sensitive plants | |
| 1,500 | 3,500 | lower yields with many plants | |
| 3,500 | 6,500 | only salt-compatible plants | |
| 6,500 | 8,000 | lower yields with salt-tolerant plants | |
| urban sewage | ? | ? | strongly fluctuating depending on the proportion of rain or sewage from roads sprinkled with thawing agent salt |
See also
- Saltwater intrusion , the penetration of saltwater into groundwater
- Brine
- Salinity
- Isotonic saline solution
- Distilled water
Web links
Individual evidence
- ↑ A. Goudie: Physical Geography - An Introduction , 4th Edition. Spektrum Akademischer Verlag, Munich, 2002, ISBN 3-8274-1872-0 .