What does seawater consist of: composition in percentages and density

The sea covers most of the planet Earth. But what do we know about him? What does seawater consist of? What are its physical properties? What is the difference between sea water and drinking water? And how to make from one another? We will try to answer all these questions in turn.

Just salt water?

Many people know what the sea tastes like, and those who do not know, guess. It's salty. But is it really possible to create a sea at home, just mixing salt and water? This is not quite true. The amount of ordinary water in the sea is 96.5%. The remaining 3.5% is 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 impurities that make water so salty are not ordinary cooking salt. In fact, all elements from the Mendeleyev periodic system are dissolved in the sea . Their presence is minimal, but undeniable.

In that very expedition, 77 water samples were taken in different regions of the World Ocean. 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, we will analyze below. At the same time we learn what the sea water consists of.

Consistency of salt composition

It is this discovery, also called the law of Ditmar, that was made in the round-the-world expedition of the late 19th century. Chemist, whose name was given to this pattern, found out that in sea water the quantitative ratio of the main ions is almost invariably 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 carrying out various hydrochemical studies.

The main ions, i.e., substances in an amount of more than 0.01%, constitute the bulk of the salts. They mainly affect the physical and chemical properties of sea water. Their number depends on various factors, including the environmental conditions. But with the 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 the sea water consists of.

As we can see, most of the chlorides make up. Taking into account the consistency of the salt composition on the basis of these data, it is possible to determine the total composition of the sea water sample. To do this, calculate the concentration of chlorine, and on the basis of the data obtained, learn by the method of the ratio, what proportion make up the remaining elements.

Physical properties

Like any other substance, sea water has different characteristics that scientists learn as a result of research. These data give an idea of many processes that occur at depth and affect our planet. For example, not everyone knows that water has the ability to contract. Under the pressure of the mass acting on it from above, it can change the volume.

On the surface it is almost imperceptible, but the deeper, the more distinct this feature becomes. Under pressure in hundreds of atmospheres, the compressibility reaches a rather large scale. Scientists claim that if not for this property of water, the ocean level would be 30 meters higher. In this case, the surface of the Earth would look quite different.

Salinity

We have already found out how much salt is in the sea water, and we know that its quantity is practically unchanged. Nevertheless, it varies a little - from 33 to 37 ‰, with rare exceptions. The average value is 34.72 . This indicator depends on the amount of precipitation falling in this or that region, the air temperature that affects the intensity of evaporation, 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 figure in its northern part is 35.06 . The lowest value belongs to the Pacific Ocean. Nevertheless, there are reservoirs in which the salinity index significantly exceeds the averaged values. They include the Mediterranean and the Red Sea. High air temperatures, high evaporation intensity and low rainfall raise the salinity level 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 related.

Some argue that sea water contains 5 ‰ salt. But such an indicator is extremely rare, only in mineral lakes. For example, the salinity level of the Sea of Azov is 11 ‰, Black - 18 ‰, Red - 41 ‰, and Dead - 300 .

Temperature

It would be naive to believe that this indicator is the same for all sea water in the world. The air temperature in regions close to the poles is lowered to the minimum mark. On the equator, on the contrary, the weather is always hot. But the range of changes in water temperature is much lower, it varies from -2 to 30 ^о С. The average figure in the entire World Ocean is only 3.73 ^о С. And on the surface water is several times warmer than at a depth of 2-5 thousand. M.

It may cause some confusion that the temperature of sea water in some regions drops to -2 ° C. Everyone knows that at 0 ° C H ₂ O turns into ice. So it is, but sea water, as we have already found out, includes impurities that change its characteristics, including the freezing point. The higher the percentage of salinity, the lower this value. For example, with a relatively small amount of salt in water (24.7 ‰), the freezing point will be -1.33 ° C.

Density

The smallest changes in this indicator cause the movement of water and lead to the appearance of vertical and horizontal flows. That is why the density of sea water is studied in any oceanographic 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 sea water at a salinity of 35 ‰ is 1027.81 kg / m ³ . This difference arises from the impurities that make up its composition. The more salt is contained in sea water, the higher the density index. Usually its value ranges from 1025 to 1033 kg / m ³ .

In addition, the density of sea water varies depending on the depth: the closer to the surface, the lower it is. But there are exceptions. For example, with intensive evaporation associated with high air temperature, salinity increases on the surface. Accordingly, the density of the sea in the upper layers also increases.

Chemical composition

As we found out above, the amount of impurities in sea water is approximately 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 said that the mineral composition of sea water and blood is approximately the same. In 1910, AB Mulloun confirmed this conjecture. In his opinion, a set of chemicals in sea water of the period when the first bony and cartilaginous fish appeared is analogous 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 given in the table below.

This list may differ slightly in different regions. For example, the composition of the sea water of the Black Sea is saturated with hydrogen sulfide, since the sulfate-reducing bacteria are particularly active here.

Where does the salt come from?

We have already found out the composition of the sea water in percents. But where do all these substances come from and why does the ocean taste like that?

In fact, salt is contained not only in sea water, but also in freshwater reservoirs. Only the concentration of minerals there is so low that it can not be recognized without special analysis. Rivers wash out of the soil on their way the salt, which later fall into the ocean. Under the influence of temperature, water in the sea evaporates, and the minerals remain in place.

But even if such a process lasted for many years, the sea water would not become so salty. Volcanic activity in the earth's crust started everything. Magma, coming to the surface, mixed with water and saturates it with a variety of mineral substances. That is why the chemical composition of the ocean was formed about 1 billion years ago, when volcanic activity was the most active.

Can I drink it?

Surely in books or films you have met statements that sea water can not be drunk in any case? But why? After all, it is the same water as any other, only with 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 for their removal from the body it will take several times more H ₂ O than was drunk from the beginning. That's why after any salty food so want to drink. And in sea water, as we have already explained, the average salinity is almost 35 ‰. This is very much.

In the 1950s, a physician and part-time traveler Alain Bambar proved from his own experience that sea water without harm to health can be drunk within a week. But to verify this statement is not worth it.

But is it possible that all the water in the World Ocean is wasted and can not be used for drinking at all? Maybe, but only after passing the desalination process.

How to get rid of salt?

We found out what seawater consists of. But for it to become suitable for drinking, the amount of impurities in it should be reduced by almost 70 times. But how to achieve this result?

There are several ways to desalinate water: ion exchange, distillation, electrodialysis, etc. The most effective are those that require the least expenditure of energy and finance. The most common method is distillation, but reverse osmosis is equally popular. In this case, high pressure is used to purify water. The result is 16 000 liters for only 1 dollar.

The method of electrodialysis, as is clear from the name, is carried out with the help of electrodes. At the moment of turning on the current, the cations and anions, which we mentioned at the very beginning of the article, tend to the cathode and the anode, respectively, through special membranes. The water between the electrodes is gradually desalinated.

The Benefits of Sea Water

Often those who suffer from respiratory diseases are sent to rest to the coast. This is correct, since seawater has a beneficial effect on the lungs, bronchi and ligaments. The liquid saturated with minerals disinfects and destroys pathogens. What else is it useful?

Stay in the sea climate and bathing in salt water have a restorative effect on the human body, and also improve the endocrine system. The result is increased immunity.

Contained in sea water, bromine, calcium and iodine contribute to strengthening tooth enamel and gums when rinsing. For best results, rinse your mouth several times a week for 2-3 minutes. Of course, only specially purified sea water, which can be found in the pharmacy, is suitable for these purposes. Before use, it must be heated to room temperature.

Sea water is a good antiseptic. It promotes healing of small wounds and abrasions, reduces itching from insect bites.