The sea covers most of the planet Earth. But what do we know about him? What does sea water consist of? What are its physical properties? How is sea water different from drinking? And how to make one from the other? We will try to answer all these questions in turn.
Just salt water?
Many people know what the sea tastes like, and those who don’t know guess. It is salty. But is it possible to create the sea of the house, just by mixing salt and water? This is not entirely true. The amount of ordinary water in the sea is 96.5%. The remaining 3.5% are impurities. Their exact composition was found out only at the end of the 19th century, during a round-the-world expedition. But long before that, scientists knew that the impurities that make water so salty are not ordinary table salt. In fact, all elements from the periodic table are dissolved in the sea. Their presence is minimal, but undeniable.
In the same expedition, 77 water samples were taken in different regions of the oceans. Then an amazing discovery was made: despite the huge amount of sea water on the Earth’s surface, the percentage of the main ions in it always remains unchanged. What this means is discussed below. At the same time we learn what sea water consists of.
Constancy of salt composition
It was this discovery, also called the law of Dietmar, that was made during a world expedition of the late 19th century. The chemist, whose name was given to this pattern, found that in sea water the quantitative ratio of the main ions is almost unchanged in different regions of the planet. The proportion of other substances is so small that it is not significant and is not taken into account when conducting various hydrochemical studies.
The main ions, i.e., substances in an amount of more than 0.01%, comprise the bulk of the salts. They mainly affect the physical and chemical properties of sea water. Their number depends on various factors, including environmental conditions. But with a total salt concentration in sea water equal to 35.16 ‰, the masses of impurities have a clear value, given in the table below. Let's see what sea water consists of.
Cations | Anions |
Name | Amount, g / kg | Name | Amount, g / kg |
Strontium | 0.014 | Fluoride | 0.001 |
Potassium | 0.387 | Boric acid | 0,026 |
Calcium | 0.408 | Bromides | 0,066 |
Magnesium | 1,297 | Hydrocarbonate | 0.143 |
Sodium | 10,764 | Sulphates | 2,701 |
| | Chlorides | 19,353 |
As we can see, most of the chloride. Taking into account the constancy of the salt composition, based on these data, it is possible to determine the complete composition of the sea water sample. To do this, calculate the concentration of chlorine, and on the basis of the data obtained, find out by the ratio method what proportion of the remaining elements.
Physical properties
Like any other substance, seawater has various characteristics that scientists will learn from research. These data allow us to get an idea of many processes occurring in depth and affecting our planet. For example, not everyone knows that water has the ability to compress. Under the pressure of the mass acting on it from above, it can change the volume.
On the surface, this is almost imperceptible, but the deeper, the more distinct this feature becomes. Under pressure of hundreds of atmospheres, compressibility reaches a fairly large scale. Scientists claim that if it were not for this property of water, the ocean level would be 30 meters higher. In this case, the Earth’s surface would look very different.
Salinity
We have already figured out how much salt is in sea water, and we know that its amount is practically unchanged. Nevertheless, it varies slightly - from 33 to 37 ‰, with rare exceptions. The average value is 34.72 ‰. This indicator depends on the amount of precipitation falling in a particular region, the air temperature affecting the evaporation rate, and the number of fresh water bodies directly connected to the sea.
The highest percentage of salinity is recorded in the Atlantic Ocean. The average in its northern part is 35.06 ‰. The least importance belongs to the Pacific Ocean. Nevertheless, there are water bodies in which the salinity index significantly exceeds the average values. These include the Mediterranean and Red Seas. High air temperatures, high evaporation rates and low rainfall raise salinity to a record 38-42 ‰. In general, the composition of the sea water of the Black Sea and many others is approximately the same. Probably the fact is that they are all interconnected.
Some claim that sea water contains 5 ‰ of salt. But such an indicator is extremely rare, only in mineral lakes. For example, the
salinity of the Sea of Azov is 11 ‰, the Black is 18 ‰, the Red is 41 ‰, and the Dead is 300 ‰.
Temperature
It would be naive to believe that this indicator is the same for all seawater in the world. The air temperature in regions close to the poles drops to minimum levels. At the equator, on the other hand, steadily hot weather is always observed. But the range of changes in water temperature is much lower, it ranges from -2 to 30 ° C. The average indicator in the entire oceans is only 3.73 ° C. Moreover, on the surface the water is several times warmer than at a depth of 2-5 thousand. m
It may cause some bewilderment that the temperature of sea water in some regions drops to -2 . Everyone knows that at 0 H 2 O turns into ice. It is, but seawater, as we have already found out, includes impurities that change its characteristics, including lowering the freezing temperature. The higher the percentage of salinity, the lower this indicator. For example, with a relatively small amount of salt in water (24.7 ‰), the freezing temperature will be -1.33 ° C.
Density
The slightest changes in this indicator cause the movement of water and lead to the emergence of vertical and horizontal flows. That is why the density of sea water is studied in any oceanological research. It is measured in kg / m 3 and represents the mass of a unit volume.
The density of fresh water at a temperature of 4 ° C is 1000 kg / m 3 , and the density of marine water at a salinity of 35 - is 1027.81 kg / m 3 . This difference occurs due to impurities that make up its composition. The more salt is contained in sea water, the higher the density will be. Usually its value ranges from 1025 to 1033 kg / m 3 .
In addition, the density of sea water varies with depth: the closer to the surface, the lower it is. But there are exceptions. For example, during intense vapors associated with high air temperatures, salinity increases on the surface. Accordingly, the density of the sea in the upper layers is growing.
Chemical composition
As we found out above, the amount of impurities in seawater is about the same. But which substances make it what it is?
It is believed that the modern chemical composition of sea water formed about 1 billion years ago. Even then, it was as salty as it is now. And especially surprising is the suggestion of R. Quinton, who in 1904 stated that the mineral composition of sea water and blood is approximately the same. In 1910, A. B. Mullun confirmed this conjecture. In his opinion, the set of chemicals in sea water of the period when the first bony and cartilaginous fish appeared is similar to the blood of all animals. But so far this hypothesis has both supporters and opponents.
Sea water contains various substances, the percentage of which is shown in the table below.
Chemical elements | Percentage |
Oxygen | 85.8 |
Hydrogen | 10.67 |
Chlorine | 2 |
Sodium | 1,07 |
Magnesium | 1.4 * 10 -1 |
Calcium | 4,5 * 10 -2 |
Sulfur | 9 * 10 -2 |
Potassium | 3.8 * 10 -2 |
Bromine | 6.5 * 10 -3 |
Carbon | 3,5 * 10 -3 |
Strontium | 1 * 10 -3 |
Boron | 4,5 * 10 -4 |
Fluorine | 1 * 10 -4 |
Silicon | 2 * 10 -5 |
This list may vary slightly in different regions. For example, the composition of the Black Sea seawater is saturated with hydrogen sulfide, since sulfate-reducing bacteria are especially active here.
Where does salt come from?
We have already found out what is the percentage of sea water. But where do all these substances come from and why does the ocean taste like that?
In fact, salts are found not only in seawater, but also in freshwater bodies. Only the concentration of minerals there is so low that it cannot be recognized without special analysis. Rivers wash salts from their soil on their way, which later fall into the ocean. Under the influence of temperature, water in the sea evaporates, and minerals remain in place.
But even if such a process lasted for many years, sea water would not become so salty. The beginning was laid by volcanic activity that takes place in the earth's crust. Magma, coming to the surface, mixes with water and saturates it with a variety of
minerals. That is why the chemical composition of the ocean formed about 1 billion years ago, when volcanic activity was most active.
Can I drink it?
Surely in books or films have you come across allegations that sea water should not be drunk in any case? But why? After all, this is the same water as any other, with only a small amount of impurities. In fact, it is because of them that it is unfit for drinking.
The amount of salt in sea water is so great that to remove them from the body you will need several times more H 2 O than was originally drunk. That is why after any salty food you are so thirsty. And in seawater, as we have already found out, the average salinity is almost 35 ‰. This is a lot.
In the 1950s, the doctor and part-time traveler Alain Bambar proved by his own experience that sea water can be drunk without harm to health for a week. But check on yourself this statement is not worth it.
But is it possible that all the water in the oceans is wasted and cannot be used for drinking at all? Maybe, but only after the desalination process.
How to get rid of salt?
We found out what sea water consists of. But in order to make it potable, the amount of impurities in it must be reduced by almost 70 times. But how to achieve such a result?
There are several ways to desalinate water: ion exchange, distillation, electrodialysis, etc. The most effective are those that require the least energy and finance. The most common way is distillation, but reverse osmosis is no less popular. In this case, high pressure is used when treating water. The result is 16,000 liters for just $ 1.
The electrodialysis method, as the name implies, is carried out using electrodes. At the moment the current is turned on, cations and anions, which we spoke about at the very beginning of the article, tend to the cathode and anode, respectively, through special membranes. Water between the electrodes is gradually desalinated.
The benefits of sea water
Often those who suffer from respiratory diseases are sent to rest on the coast. This is correct, since sea water has a beneficial effect on the lungs, bronchi and ligaments. A liquid saturated with minerals disinfects and destroys pathogenic microbes. What else is it useful for?
Staying in a marine climate and swimming in salt water have a restorative effect on the human body, as well as improve the functioning of the endocrine system. The result is increased immunity.
The bromine, calcium and iodine contained in sea water help strengthen tooth enamel and gums when rinsing. To achieve the best effect, rinse your mouth several times a week for 2-3 minutes. Of course, only specially purified sea water, which can be found in a pharmacy, is suitable for these purposes. Before use, it must be warmed to room temperature.
Sea water is a good antiseptic. It promotes the healing of small wounds and abrasions, reduces itching from insect bites.