Freezing point of salt water table. Scientific electronic library

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.

At what temperature does water freeze? It would seem to be the simplest question, which even a child can answer: the freezing temperature of water at normal atmospheric pressure at 760 mm Hg is zero degrees Celsius.

However, water (despite its extremely wide distribution on our planet) is the most mysterious and incompletely studied substance, so the answer to this question requires a detailed and reasoned conversation.

In Russia and Europe, temperature is measured on the Celsius scale, most high value which has a mark of 100 degrees.
The American scientist Fahrenheit developed his own scale with 180 divisions.
There is another unit of temperature measurement - the kelvin, named after the English physicist Thomson, who received the title of Lord Kelvin.

Conditions and types of water

Water on planet Earth can take on three main physical states: liquid, solid and gaseous, which can be transformed into different shapes, simultaneously coexisting with each other (icebergs in sea water, water vapor and ice crystals in clouds in the sky, glaciers and free-flowing rivers).

Depending on the characteristics of origin, purpose and composition, water can be:

fresh;
mineral;
nautical;
drinking (we include tap water here);
rain;
thawed;
salty;
structured;
distilled;
deionized.

The presence of hydrogen isotopes makes water:

light;
heavy (deuterium);
superheavy (tritium).

We all know that water can be soft or hard: this indicator is determined by the content of magnesium and calcium cations.

Each of the types and aggregate states of water we have listed has its own freezing and melting point.

Freezing point of water

Why does water freeze? Ordinary water always contains some suspended particles of mineral or organic origin. These can be tiny particles of clay, sand or house dust.

When the temperature environment drops to certain values, these particles take on the role of centers around which ice crystals begin to form.

Air bubbles, as well as cracks and damage on the walls of the vessel containing water, can also become crystallization nuclei. The speed of the water crystallization process is largely determined by the number of these centers: the more of them, the faster the liquid freezes.

Under normal conditions (at normal atmospheric pressure), the temperature of the phase transition of water from liquid to solid is 0 degrees Celsius. It is at this temperature that water freezes outside.

Why does hot water freeze faster than cold water?

Hot water freezes faster than cold water - this phenomenon was noticed by Erasto Mpemba, a schoolboy from Tanganyika. His experiments with ice cream mixtures showed that the rate of freezing of heated masses was significantly higher than that of cold ones.

One of the reasons for this interesting phenomenon, called the “Mpemba paradox,” is the higher heat transfer of hot liquid, as well as the presence of a larger number of crystallization nuclei in it compared to cold water.

Are the freezing point of water and altitude related?

When pressure changes, often associated with being at different altitudes, the freezing point of water begins to differ radically from the standard one characteristic of normal conditions.
Crystallization of water at altitude occurs at the following temperature values:

Paradoxically, at an altitude of 1000 m, water freezes at 2 degrees Celsius;
at an altitude of 2000 meters this occurs already at 4 degrees Celsius.

The highest freezing temperature of water in the mountains is observed at an altitude of over 5,000 thousand meters (for example, in the Fan Mountains or the Pamirs).

How does pressure affect the process of water crystallization?

Let's try to link the dynamics of changes in the freezing temperature of water with changes in pressure.

At a pressure of 2 atm, water will freeze at a temperature of -2 degrees.
At a pressure of 3 atm, the temperature of -4 degrees Celsius will begin to freeze water.

With increased pressure, the temperature at which the water crystallization process begins decreases, and the boiling point increases. At low pressure, a diametrically opposite picture is obtained.

That is why in high altitude conditions and a rarefied atmosphere it is very difficult to boil even eggs, since the water in the pot boils already at 80 degrees. It is clear that it is simply impossible to cook food at this temperature.

At high pressure, the process of melting the ice under the blades of the skates occurs even at very low temperatures, but it is thanks to it that the skates glide along the icy surface.

The freezing of the runners of heavily loaded sleds in the stories of Jack London is explained in a similar way. Heavy sleds putting pressure on the snow cause it to melt. The resulting water makes them easier to slide. But as soon as the sledges stop and stay in one place for a long time, the displaced water freezes and freezes the runners to the road.

Crystallization temperature of aqueous solutions

Being an excellent solvent, water easily reacts with various organic and inorganic substances, forming a mass of sometimes unexpected chemical compounds. Of course, each of them will freeze at different temperatures. Let's show this in a visual list.

The freezing point of a mixture of alcohol and water depends on percentage it contains both components. How more water added to the solution, the closer to zero its freezing point. If there is more alcohol in the solution, the crystallization process will begin at values close to -114 degrees.
It is important to know that water-alcohol solutions do not have a fixed freezing point. Usually they talk about the temperature at the beginning of the crystallization process and the temperature of the final transition to the solid state.
Between the beginning of the formation of the first crystals and the complete solidification of the alcohol solution there is a temperature interval of 7 degrees. Thus, the freezing point of water with 40% alcohol concentration at the initial stage is -22.5 degrees, and the final transition of the solution into the solid phase will occur at -29.5 degrees.

The freezing point of water with salt is closely related to the degree of its salinity: the more salt in the solution, the lower the position of the mercury column it will freeze.

To measure the salinity of water, a special unit is used - “ppm”. So, we have established that the freezing point of water decreases with increasing salt concentration. Let's explain this with an example:

The salinity level of ocean water is 35 ppm, while its average freezing point is 1.9 degrees. The salinity of the Black Sea waters is 18-20 ppm, so they freeze at a higher temperature with a range from -0.9 to -1.1 degrees Celsius.

The freezing point of water with sugar (for a solution whose molality is 0.8) is -1.6 degrees.
The freezing point of water with impurities largely depends on their quantity and the nature of the impurities included in the aqueous solution.
The freezing point of water with glycerin depends on the concentration of the solution. A solution containing 80 ml of glycerin will freeze at -20 degrees; when the glycerin content decreases to 60 ml, the crystallization process will begin at -34 degrees, and the start of freezing of a 20% solution is minus five degrees. As you can see, there is no linear relationship in this case. To freeze a 10% glycerin solution, a temperature of -2 degrees will be sufficient.
The freezing point of water with soda (meaning caustic alkali or caustic soda) presents an even more mysterious picture: a 44% caustic solution freezes at +7 degrees Celsius, and 80% at + 130.

Freezing of fresh water bodies

The process of ice formation in freshwater bodies occurs in a slightly different temperature regime.

The freezing point of water in a lake, just like the freezing point of water in a river, is zero degrees Celsius. Freezing of the cleanest rivers and streams begins not from the surface, but from the bottom, on which crystallization nuclei are present in the form of particles of bottom silt. At first, driftwood and aquatic plants are covered with a crust of ice. It's only worth bottom ice rise to the surface, as the river instantly freezes through.
The frozen water on Lake Baikal can sometimes cool to sub-zero temperatures. This happens only in shallow water; the water temperature can be thousandths and sometimes hundredths of one degree below zero.
The temperature of Baikal water under the very crust of the ice cover, as a rule, does not exceed +0.2 degrees. In the lower layers it gradually increases to +3.2 at the bottom of the deepest basin.

Freezing point of distilled water

Does distilled water freeze? Let us remember that for water to freeze, it is necessary to have certain centers of crystallization in it, which can be air bubbles, suspended particles, as well as damage to the walls of the container in which it is located.

Distilled water, completely devoid of any impurities, does not have crystallization nuclei, and therefore its freezing begins at very low temperatures. The initial freezing point of distilled water is -42 degrees. Scientists managed to achieve supercooling of distilled water to -70 degrees.

Water that has been exposed to very low temperatures without crystallizing is called “supercooled.” You can place a bottle of distilled water in the freezer to achieve hypothermia, and then demonstrate a very impressive trick - watch the video:

By gently tapping a bottle taken out of the refrigerator, or throwing a small piece of ice into it, you can show how instantly it turns into ice that looks like elongated crystals.

Distilled water: does this purified substance freeze under pressure or not? Such a process is possible only in specially created laboratory conditions.

Freezing point of salt 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.

Falling on unfrozen fresh river water, ordinary snow with a melting point 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 sea water cools to the appropriate freezing temperature, primary ice crystals begin to appear in it, in the form of very thin hexagonal prisms, similar to 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 use for drinking water usually snow, and when there is no snow, 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 waves break the fast ice. The parts that come off from it float downstream and are carried away by the wind. This is how floating ice. 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 the fragmentation of 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 sledding. 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 mentioned above, creates the unity of the World Ocean.

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The water in the seas and oceans is very different from river and lake water. It is salty - and this determines many of its properties. The freezing temperature of sea water also depends on this factor. It is not equal to 0 °C, as is the case with fresh water. To become covered with ice, the sea requires stronger frost.

It is impossible to say unambiguously at what temperature sea water freezes, since this indicator depends on the degree of its salinity. It is different in different places of the world's oceans.

The most salty is the Red Sea. Here the concentration of salt in the water reaches 41‰ (ppm). The least amount of salt in the waters of the Baltic Gulf is 5‰. In the Black Sea, this figure is 18‰, and in the Mediterranean - 26‰. The salinity of the Sea of Azov is 12‰. And if we take the average, the salinity of the seas is 34.7‰.

The higher the salinity, the more seawater must cool to become a solid.

This is clearly seen from the table:

Salinity, ‰	Freezing temperature, °C	Salinity, ‰	Freezing temperature, °C
0 (fresh water)		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

Where the salinity is even higher, such as in Lake Sivash (100 ‰), Kara-Bogaz-Gol Bay (250 ‰), in the Dead Sea (over 270 ‰), water can freeze only with a very large minus - in the first case - at -6.1 °C, in the second - below -10 °C.

The average for all seas can be taken as -1.9 °C.

Stages of freezing

It is very interesting to watch how sea water freezes. It is not immediately covered with a uniform ice crust, like fresh water. When part of it turns into ice (which is fresh), the rest becomes even more salty, and requires even stronger frost to freeze.

Types of Ice

As the sea cools, different types of ice form:

snowflake;
sludge;
needles;
salo;
nilas.

If the sea has not yet frozen, but is very close to it, and snow falls at this time, it does not melt upon contact with the surface, but is saturated with water and forms a viscous porridge-like mass, which is called snow. Freezing, this porridge turns into slush, which is very dangerous for ships caught in a storm. Because of it, the deck is instantly covered with an ice crust.

When the thermometer reaches the level required for freezing, ice needles begin to form in the sea - crystals in the form of very thin hexagonal prisms. Having collected them with a net, washed off the salt from them and melted them, you will find that they are fresh.

At first, the needles grow horizontally, then they take a vertical position, and only their bases are visible on the surface. They resemble spots of fat in cooled soup. Therefore, ice at this stage is called lard.

When it gets even colder, the lard begins to freeze and forms an ice crust, as transparent and fragile as glass. Such ice is called nilas, or bottle. It is salty, although it is formed from unleavened needles. The fact is that during freezing, the needles capture tiny drops of surrounding salt water.

Only in the seas is there such a phenomenon as floating ice. It arises because the water here cools faster off the coast. The ice that forms there freezes to the coastal edge, which is why it is called fast ice. As frosts intensify during calm weather, it quickly captures new territories, sometimes reaching tens of kilometers in width. But it's worth the climb strong wind- and the fast ice begins to break into pieces of various sizes. These ice floes, often of enormous size (ice fields), are carried by wind and current throughout the sea, causing problems for ships.

Melting temperature

Sea ice does not melt at the same temperature at which sea water freezes, as one might think. It is less salty (on average 4 times), so its transformation back into liquid begins before this mark is reached. If the average freezing point of sea water is -1.9 °C, then the average melting temperature of the ice formed from it is -2.3 °C.

Salt Water Freezing: Video

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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. Most low temperature freezing has a saturated solution. 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.

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