Freezing point of salt water table. At what temperature does sea water freeze? Photos and videos with experiments

Young naturalists are always haunted by seemingly simple questions. This is the temperature at which it usually freezes sea water? Everyone knows that zero degrees is not enough to turn the sea surface into a good skating rink. But at what temperature does this happen?

What does sea water consist of?

How do the contents of the seas differ from fresh water? The difference is not so great, but still:

Much more salt.
Magnesium and sodium salts predominate.
The density differs slightly, within a few percent.
Hydrogen sulfide may form at depth.

The main component of sea water, no matter how predictable it may sound, is water. But unlike the water of rivers and lakes, it contained a large number of sodium and magnesium chlorides.

Salinity is estimated at 3.5 ppm, but to make it more clear - at 3.5 thousandths of a percent of the total composition.

And even this, not the most impressive figure, provides the water with not only a specific taste, but also makes it unfit for drinking. There are no absolute contraindications, sea water is not poison or a toxic substance and nothing bad will happen from a couple of sips. It will be possible to talk about the consequences if a person at least throughout the day. Also, the composition of sea water includes:

Fluorine.
Bromine.
Calcium.
Potassium.
Chlorine.
Sulfates.
Gold.

True, in percentage All these elements are much less than salts.

Why can't you drink sea water?

We have already briefly touched on this topic, let's look at it in a little more detail. Together with sea water, two ions enter the body - magnesium and sodium.

Sodium	Magnesium
Participates in maintaining water-salt balance, one of the main ions along with potassium.	The main effect is on the central nervous system.
With increasing quantity Na In the blood, fluid leaves the cells.	It is eliminated from the body very slowly.
All biological and biochemical processes are disrupted.	An excess in the body leads to diarrhea, aggravating dehydration.
Human kidneys are not able to cope with so much salt in the body.	The development of nervous disorders and inadequate condition is possible.

It cannot be said that a person does not need all these substances, but needs always fit within a certain framework. After drinking a few liters of this water, you will go too far beyond their limits.

However, today an urgent need for drinking sea water may arise only among victims of shipwrecks.

What determines the salinity of sea water?

Seeing a slightly higher number 3.5 ppm , you might think that this is a constant for any seawater on our planet. But it’s not that simple; salinity depends on the region. It just so happens that the further north the region is located, the greater this value.

The South, on the contrary, cannot boast of such salty seas and oceans. Of course, all rules have their exceptions. The salt levels in the seas are usually slightly lower than in the oceans.

What could be the reason for geographic division? It is unknown, researchers take it for granted, that’s all. Perhaps the answer should be sought in earlier periods of the development of our planet. Not at the time when life began - much earlier.

We already know that the salinity of water depends on the presence in it of:

Magnesium chlorides.
Sodium chlorides.
Other salts.

Possibly in some areas earth's crust the deposits of these substances were somewhat larger than in neighboring regions. On the other hand, no one canceled sea currents, sooner or later general level should have leveled off.

So most likely the slight difference is due to climatic features of our planet. Not the most unfounded opinion, if you remember the frosts and take into account what exactly Water with a high salt content freezes more slowly.

Desalination of sea water.

Everyone has heard at least a little about desalination, some have even heard the movie “ water world"will remember. How realistic is it to put one such portable desalination machine in every home and forget about the problem for humanity forever? drinking water? Still fantasy, not actual reality.

It's all about the energy expended, because for efficient work Huge power is needed, no less than a nuclear reactor. A desalination plant in Kazakhstan operates on this principle. The idea was also presented in Crimea, but the power of the Sevastopol reactor was not enough for such volumes.

Half a century ago, before numerous nuclear disasters, it was still possible to assume that a peaceful atom would enter every home. There was even a slogan like that. But it is already clear that there is no use of nuclear micro-reactors:

In household appliances.
At industrial enterprises.
In the designs of cars and airplanes.
And generally within the city limits.

Not expected in the next century. Science can make another leap and surprise us, but for now these are all just the fantasies and hopes of careless romantics.

At what temperature can sea water freeze?

But the main question has not yet been answered. We have already learned that salt slows down the freezing of water, and the sea becomes covered with a crust of ice not at zero, but at sub-zero temperatures. But how far should thermometer readings go below zero so that residents of coastal areas do not hear the usual sound of the surf when leaving their homes?

To determine this value there is a special formula, complex and understandable only to specialists. It depends on the main indicator - salinity level. But since we have an average for this indicator, can we average temperature find freezing? Yes, sure.

If you do not need to calculate everything down to the hundredth for a specific region, remember the temperature is -1.91 degrees.

It may seem that the difference is not that big, just two degrees. But during seasonal temperature fluctuations, this can play a huge role where the thermometer does not fall below 0. It would be only 2 degrees cooler, the inhabitants of the same Africa or South America would be able to see the ice near the shore, but alas. However, we don’t think that they are very upset by such a loss.

A few words about the world's oceans.

What about the oceans, fresh water reserves, and pollution levels? Let's try to find out:

The oceans are still standing, nothing has happened to them. In recent decades, water levels have been rising. Perhaps this is a cyclical phenomenon, or perhaps the glaciers are actually melting.
There is also more than enough fresh water; it is too early to panic about this. If another worldwide conflict occurs, this time using nuclear weapons, maybe we will, like in “Mad Max,” pray for saving moisture.
This last point is very popular among conservationists. And getting sponsorship is not so difficult; competitors will always pay for black PR, especially when it comes to oil companies. But they are the ones who cause the main damage to the waters of the seas and oceans. It is not always possible to control oil production and emergency situations, and the consequences are catastrophic every time.

But the world's oceans have one advantage over humanity. It is constantly updated, and its real self-cleaning capabilities are very difficult to assess. Most likely, he will be able to survive human civilization and see its decline in a completely acceptable state. Well, then the water will have billions of years to clear itself of all the “gifts”.

It’s even hard to imagine who needs to know at what temperature sea water freezes. A general educational fact, but who will really need it in practice is a question.

Video experiment: freezing sea water

Sea water freezes at temperatures below zero degrees. The higher the salinity of sea water, the lower its freezing point. This can be seen from the following table:

Salinity in °/00	Freezing point (in degrees)	Salinity in °/00	Freezing point (in degrees)
0 (fresh water)	0	20	-1,1
2	-0,1	22	-1,2
4	-0,2	24	-1,3
6	-0,3	26	-1,4
8	-0,4	28	-1,5
10	-0,5	30	-1,6
12	-0,6	32	-1,7
14	-0,8	35	-1,9
16	-0,9	37	-2,0
18	-1,0	39	-2,1

This table shows that an increase in salinity of 2°/00 lowers the freezing point by about one tenth of a degree.

In order for water with an oceanic salinity of 35 °/00 to begin to freeze, it must be cooled below zero by almost two degrees.

When falling on unfrozen fresh river water, ordinary snow with a melting temperature of zero degrees, as a rule, melts. If this same snow falls on unfrozen sea water with a temperature of -1°, then it does not melt.

Knowing the salinity of the water, you can determine the freezing point of any sea using the table above.

Salinity of water Sea of Azov in winter about 12 °/00; therefore, water begins to freeze only at a temperature of 0°.6 below zero.

In the open part White Sea salinity reaches 25 °/00. This means that for water to freeze, it must cool below minus 1°.4.

Water with a salinity of 100 °/00 (this salinity can be found in Sivashi, separated from the Sea of Azov by the Arabat Spit) will freeze at a temperature of minus 6 °.1, and in Kara-Bogaz-Gol the salinity is more than 250 °/00, and the water only freezes when its temperature drops significantly below 10° below zero!

When salty seawater cools to the appropriate freezing point, primary ice crystals begin to appear, shaped like very thin hexagonal prisms that look like needles.

Therefore, they are usually called ice needles. Primary ice crystals that form in salty seawater do not contain salt; it remains in solution, increasing its salinity. This is easy to verify. Having collected the ice needles with a net made of very thin gauze or tulle, you need to rinse them with fresh water to wash them off. salt water and then melt in another bowl. You will get fresh water.

Ice, as you know, is lighter than water, so ice needles float. Their accumulations on the surface of the water resemble appearance grease stains on cooled soup. These accumulations are called lard.

If the frost intensifies and the surface of the sea quickly loses heat, then the fat begins to freeze and in calm weather an even, smooth, transparent ice crust appears, which the Pomors, residents of our northern coast, call nilas. It is so pure and transparent that in huts made of snow, it can be used instead of glass (of course, if there is no heating inside such a hut). If you melt nilas, the water will turn out to be salty. True, its salinity will be lower than the water from which the ice needles were formed.

Individual ice needles do not contain salt, but salt appears in the sea ice formed from them. This happens because randomly located ice needles, when frozen, capture tiny droplets of salty sea water. Thus, salt is distributed unevenly in sea ice - in separate inclusions.

Salinity sea ice depends on the temperature at which it was formed. When there is slight frost, the ice needles freeze slowly and capture little salt water. In severe frost, ice needles freeze much faster and capture a lot of salt water. In this case, the sea ice will be saltier.

When sea ice begins to melt, the first thing that melts out of it is salty inclusions. Therefore, old, multi-year polar ice, which has flown over several times, becomes fresh. Polar winterers usually use snow for drinking water, and when this is not available, old sea ice.

If during education ice is coming snow, then it, without melting, remains on the surface of sea water, is saturated with it and, freezing, forms cloudy, whitish, opaque, uneven ice - young fish. Both nilas and youngsters, when wind and waves break, break into pieces, which, colliding with each other, hit the corners and gradually turn into round ice floes - blinks. When the excitement subsides, the pancakes freeze together, forming solid pancake ice.

Off the coast, in the shallows, sea water cools down faster, so ice appears earlier than in the open sea. Usually the ice freezes to the shores, this is fast ice. If frosts are accompanied by calm weather, fast ice grows quickly, sometimes reaching a width of many tens of kilometers. But strong winds and disturbances break up the fast ice. The parts that come off from it float downstream and are carried away by the wind. This is how floating ice appears. Depending on their size, they have different names.

An ice field is floating ice with an area greater than one square nautical mile.

Floating ice longer than one cable length is called ice field debris.

Coarse ice is shorter than one cable length, but more than one tenth of a cable length (18.5 m). Finely broken ice does not exceed one tenth of a cable length, and the ice porridge consists of small pieces tumbling on the waves.

Currents and wind can push ice floes against fast ice or against each other. The pressure of the ice fields on each other causes crushing floating ice. This usually creates piles of finely broken ice.

When a single ice floe rears up and in this position freezes into the surrounding ice, it forms a ropac. Ropacas covered with snow are difficult to see from an airplane and can cause a disaster during landing.

Often, under the pressure of ice fields, ice ridges are formed - hummocks. Sometimes hummocks reach a height of several tens of meters. Hummocky ice is difficult to pass, especially for dog sled. It poses a serious obstacle even for powerful icebreakers.

A fragment of a hummock that rises above the surface of the water and is easily carried away by the wind is called a nesak. A fish that has run aground is called a stamukha.

Around Antarctica and in the Arctic Ocean there are ice mountains - icebergs. These are usually fragments of continental ice.

In Antarctica, as researchers have recently established, icebergs also form in the sea, on the continental shallows. Only part of the iceberg is visible above the surface of the water. Most of it (about 7/8) is under water. The area of the underwater part of the iceberg is always much larger than the surface area. Therefore, icebergs are dangerous for ships.

Now icebergs can be easily detected in the distance and in fog using precision radio instruments on a ship. Previously, there were cases of ship collisions with icebergs. This is how, for example, the huge ocean passenger steamer Titanic sank in 1912.

WATER CYCLE IN THE WORLD OCEAN

In the polar zones, water, as it cools, becomes denser and sinks to the bottom. From there it slowly slides towards the equator. Therefore, at all latitudes, deep waters are cold. Even near the equator, bottom waters have a temperature of only 1-2° above zero.

Since currents carry away from the equator warm water to moderate latitudes, then in its place from the depths it rises very slowly cold water. On the surface it warms up again, goes to the polar zones, where it cools, sinks to the bottom and moves along the bottom again to the equator.

Thus, in the oceans there is a kind of water cycle: water moves along the surface from the equator to the polar zones and along the bottom of the oceans - from the polar zones to the equator. This process of mixing water, along with other phenomena discussed above, creates the unity of the World Ocean.

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The table shows the thermophysical properties of a solution of calcium chloride CaCl 2 depending on temperature and salt concentration: specific heat of the solution, thermal conductivity, viscosity of aqueous solutions, their thermal diffusivity and Prandtl number. The concentration of CaCl 2 salt in the solution is from 9.4 to 29.9%. The temperature at which the properties are given is determined by the salt content in the solution and ranges from -55 to 20°C.

Calcium chloride CaCl 2 may not freeze to a temperature of minus 55°C. To achieve this effect, the salt concentration in the solution must be 29.9%, and its density will be 1286 kg/m 3.

With increasing salt concentration in a solution, not only its density increases, but also such thermophysical properties as the dynamic and kinematic viscosity of aqueous solutions, as well as the Prandtl number. For example, dynamic viscosity of CaCl 2 solution with a salt concentration of 9.4% at a temperature of 20°C is equal to 0.001236 Pa s, and when the concentration of calcium chloride in the solution increases to 30%, its dynamic viscosity increases to a value of 0.003511 Pa s.

It should be noted that the viscosity of aqueous solutions of this salt is most strongly influenced by temperature. When a calcium chloride solution is cooled from 20 to -55°C, its dynamic viscosity can increase by 18 times, and its kinematic viscosity by 25 times.

The following are given thermophysical properties of CaCl 2 solution:

, kg/m 3 ;
freezing temperature °C;
dynamic viscosity of aqueous solutions, Pa s;
Prandtl number.

Density of calcium chloride solution CaCl 2 depending on temperature

The table shows the density values of calcium chloride solution CaCl 2 of various concentrations depending on temperature.
The concentration of calcium chloride CaCl 2 in solution is from 15 to 30% at a temperature from -30 to 15°C. The density of an aqueous solution of calcium chloride increases as the temperature of the solution decreases and the salt concentration in it increases.

Thermal conductivity of CaCl 2 solution depending on temperature

The table shows the thermal conductivity values of a solution of calcium chloride CaCl 2 of various concentrations at negative temperatures.
The concentration of CaCl 2 salt in solution is from 0.1 to 37.3% at a temperature from -20 to 0°C. As the concentration of salt in a solution increases, its thermal conductivity decreases.

Heat capacity of CaCl 2 solution at 0°C

The table shows the mass heat capacity of calcium chloride solution CaCl 2 of various concentrations at 0°C. The concentration of CaCl 2 salt in the solution is from 0.1 to 37.3%. It should be noted that with increasing salt concentration in the solution, its heat capacity decreases.

Freezing point of solutions of salts NaCl and CaCl 2

The table shows the freezing temperature of solutions of sodium chloride salts NaCl and calcium CaCl 2 depending on the salt concentration. The salt concentration in the solution is from 0.1 to 37.3%. The freezing point of a saline solution is determined by the salt concentration in solution and for sodium chloride, NaCl can reach a value of minus 21.2°C for a eutectic solution.

It should be noted that sodium chloride solution may not freeze to a temperature of minus 21.2°C, and a solution of calcium chloride does not freeze at temperatures up to minus 55°C.

Density of NaCl solution depending on temperature

The table shows the density values of sodium chloride NaCl solution of various concentrations depending on temperature.
The concentration of NaCl salt in the solution is from 10 to 25%. The density values of the solution are indicated at temperatures from -15 to 15°C.

Thermal conductivity of NaCl solution depending on temperature

The table shows the thermal conductivity values of a solution of sodium chloride NaCl of various concentrations at negative temperatures.
The concentration of NaCl salt in the solution is from 0.1 to 26.3% at a temperature from -15 to 0°C. The table shows that the thermal conductivity of an aqueous solution of sodium chloride decreases as the concentration of salt in the solution increases.

Specific heat capacity of NaCl solution at 0°C

The table shows the mass specific heat capacity of an aqueous solution of sodium chloride NaCl of various concentrations at 0°C. The concentration of NaCl salt in the solution is from 0.1 to 26.3%. The table shows that with increasing salt concentration in the solution, its heat capacity decreases.

Thermophysical properties of NaCl solution

The table shows the thermophysical properties of a solution of sodium chloride NaCl depending on temperature and salt concentration. The concentration of sodium chloride NaCl in solution is from 7 to 23.1%. It should be noted that when an aqueous solution of sodium chloride is cooled, its specific heat capacity changes slightly, thermal conductivity decreases, and the viscosity of the solution increases.

The following are given thermophysical properties of NaCl solution:

solution density, kg/m3;
freezing temperature °C;
specific (mass) heat capacity, kJ/(kg deg);
thermal conductivity coefficient, W/(m deg);
dynamic viscosity of the solution, Pa s;
kinematic viscosity of the solution, m 2 /s;
thermal diffusivity coefficient, m 2 /s;
Prandtl number.

Density of solutions of sodium chloride NaCl and calcium CaCl 2 depending on concentration at 15°C

The table shows the density values of solutions of sodium chloride NaCl and calcium CaCl 2 depending on the concentration. The concentration of NaCl salt in the solution is from 0.1 to 26.3% at a solution temperature of 15°C. The concentration of calcium chloride CaCl 2 in the solution ranges from 0.1 to 37.3% at a temperature of 15°C. The density of sodium and calcium chloride solutions increases with increasing salt content.

Volume expansion coefficient of solutions of sodium chloride NaCl and calcium CaCl 2

The table gives the values of the average coefficient of volumetric expansion of aqueous solutions of sodium chloride NaCl and calcium CaCl 2 depending on concentration and temperature.
The coefficient of volumetric expansion of a NaCl salt solution is indicated at a temperature from -20 to 20°C.
The coefficient of volumetric expansion of a CaCl 2 chloride solution is presented at temperatures from -30 to 20°C.

Sources:

Danilova G.N. et al. Collection of problems on heat transfer processes in the food and refrigeration industry. M.: Food industry, 1976.- 240 p.

If you cool a solution of a salt in water, you will find that the freezing point has decreased. Zero degrees have passed, but hardening does not occur. Only at a temperature several degrees below zero will crystals appear in the liquid. These are crystals pure ice, salt does not dissolve in solid ice.

The freezing point depends on the concentration of the solution. By increasing the concentration of the solution, we will decrease the crystallization temperature. A saturated solution has the lowest freezing point. The decrease in the freezing point of a solution is not at all small: for example, a saturated solution table salt in water it will freeze at - 21 °C. With the help of other salts, an even greater decrease in temperature can be achieved; calcium chloride, for example, allows you to bring the solidification temperature of the solution to -55°C.

Let us now consider how the freezing process occurs. After the first ice crystals fall out of the solution, the strength of the solution will increase. Now the relative number of foreign molecules will increase, interference with the process of water crystallization will also increase, and the freezing point will drop. If the temperature is not lowered further, crystallization will stop.

As the temperature decreases further, crystals of water (solvent) continue to be released. Finally, the solution becomes saturated. Further enrichment of the solution with the dissolved substance becomes impossible, and the solution freezes immediately, and if you examine the frozen mixture under a microscope, you can see that it consists of ice crystals and salt crystals.

Thus, the solution freezes differently than a simple liquid. The freezing process extends over a large temperature interval.

What happens if you sprinkle salt on some icy surface? The answer to the question is well known to janitors: as soon as the salt comes into contact with the ice, the ice will begin to melt. For the phenomenon to take place, it is necessary, of course, that the freezing point of a saturated salt solution be lower than the air temperature. If this condition is met, then the ice-salt mixture is in a foreign state region, namely in the region of stable existence of the solution. Therefore, the mixture of ice and salt will turn into a solution, i.e., the ice will melt and the salt will dissolve in the resulting water. Eventually, either all the ice will melt, or a solution will form at a concentration whose freezing point is equal to the temperature of the medium.

An area of 100 m2 of yard is covered with an ice crust of 1 cm - this is quite a lot of ice, about 1 ton. Let's calculate how much salt is needed to clean the yard if the temperature is -3°C. A salt solution with a concentration of 45 g/l has this crystallization (melting) temperature. Approximately 1 liter of water corresponds to 1 kg of ice. This means that to melt 1 ton of ice at -3°C you need 45 kg of salt. In practice, they use much smaller quantities, since they do not achieve complete melting of all the ice.

When ice and salt are mixed, the ice melts and the salt dissolves in the water. But melting requires heat, and ice takes it from its surroundings. Thus, adding salt to ice causes the temperature to drop.

We are now used to buying factory-made ice cream. Previously, ice cream was prepared at home, and the role of the refrigerator was played by a mixture of ice and salt.

In the section on the question what can be achieved the lowest temperature of a water-salt solution of ordinary (table, NaCl) salt asked by the author European the best answer is By adding salt to water, the rate of ice melting increases and the melting temperature of ice drops lower. This is explained by the fact that the addition of salt causes a weakening of molecular cohesion and destruction of the ice crystal lattices. The melting of the ice-salt mixture proceeds with the removal of heat from environment, as a result of which the surrounding air cools and its temperature decreases. As the salt content in the ice-salt mixture increases, its melting point decreases. The salt solution with the lowest melting point is called eutectic, and its melting point is called the cryohydrate point. The cryohydrate point for an ice-salt mixture with table salt is -21.2°C, with a salt concentration in the solution of 23.1% relative to the total mass of the mixture, which is approximately equal to 30 kg of salt per 100 kg of ice. With a further increase in salt concentration, there is not a decrease in the melting temperature of the ice-salt mixture, but an increase in the melting temperature (at a 25% salt concentration in the solution relative to the total mass, the melting temperature rises to -8°C).
When an aqueous solution of table salt is frozen in a concentration corresponding to the cryohydrate point, a homogeneous mixture of ice crystals and salt is obtained, which is called a eutectic solid solution.
The melting point of the eutectic solid solution of table salt is -21.2°C, and the heat of fusion is 236 kJ/kg. The eutectic solution is used for zero-torque cooling. To do this, a eutectic solution of table salt is poured into zeros - tightly sealed forms - and frozen. Frozen zeros are used to cool counters, cabinets, refrigerated portable refrigerator bags, etc. (open the freezer of a household refrigerator - you will find such a container). In trade, ice-salt cooling was widely used before the mass production of equipment with a machine cooling method.

Answer from Dry out[guru]
the most low temperature from any temperature - absolute zero, about - 273 degrees Celsius

Answer from Olya[expert]
the temperature depends on the concentration of salt in the solution; the higher the concentration, the lower the freezing point. I won’t tell you the exact numbers, because... the reference book was taken away from me for a while)) but if we proceed from the fact that sea water is a saline solution, then we can conclude that the freezing point is much below zero.... -15-20 degrees

Answer from capable[guru]
A 22.4% aqueous solution of NaCl freezes at 21.2 °C
Answer
link
to the question
Aqueous NaCl solution "crystallization temperature"

Answer from Yorgey Neznamov[newbie]
Table 10.8. Freezing point of NaCl solution
NaCl content, g in 100 g of water Freezing point, ? C
1,5 - -0,9
3,0 - - 1,8
4,5 - -2,6
5,9 - -3,5
7,5 - -4,4
9,0 - -5,4
10,6 - -6,4
12,3 - -7,5
14,0 - -8,6
15,7 - -9,8
17,5 - -11,0
19,3 - - 12,2
21,2 - -13,6
23,1 - - 15,1
25,0 - - 16,0
26,9 - -18,2
29,0 - -20,0
30,1 - -21,2

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