Secrets of boiling salted and fresh water. Why salt water boils faster than the usual, is it true so

Boiling is called the charging process, which occurs when the fluid is brought to the boiling point. Each person since the school desk knows that boiling water occurs at t \u003d 100 ° C. But many are interested in the question, what water boils faster: salty or fresh?

What is the boiling process

Boiling - a rather complex process consisting of four stages:

• The first stage It is characterized by the appearance of small air bubbles that appear both on the surface of the liquid and side. Their appearance is the result of expanding air bubbles in microscopic tank cracks.
• During the second stage It can be seen that bubbles increase in volume and their increasing amount turns out to be top. This phenomenon is explained by increasing the temperature at which the pressure on bubbles increases. Thanks to the archimedema force, they turn out to be on the surface. If she did not have time to warm up to boiling point (100 ° C), then bubbles go to the bottom where the water is hotter. The noise characteristic of boiling is created by increasing and decreasing bubbles.
• At the third stage There is a mass of bubbles, which climbing the surface causes a short-term turbidity of water.
• Fourth Stage It is characterized by intense drone and the appearance of large bubbles, which blowing up, create splashes. The latter say that water has rippled. There is water vapor, and the water is published characteristic of boiling sounds.

Boiling fresh water

Boiling water is called water brought to a boil. During this process, a copious formation of a steam occurs, which is accompanied by the release of free oxygen molecules from the composition of the boiling fluid. Due to the long-term effects of high temperatures, microbes and pathogenic bacteria die in boiling water. Therefore, with the poor quality of tap water, it is undesirable to use it in the raw form.

Fresh, but tough water has a salt in its composition. During the boiling, they form a kettle on the walls of the kettle, which is more often called screaming. Boiling water is usually used to prepare hot drinks or disinfection of fruits or vegetables.

When salty water boats

As the experiments show, the boiling point of the salt water is above the boiling point of fresh. Therefore, we can conclude that fresh water boils faster. In salty water contains chlorine and sodium ions, which are among water molecules. The hydration process occurs between them - the addition of water molecules to salt ions.

It is worth noting that the hydration bond is much stronger than aqueous intermolecular. Therefore, during the boiling of fresh water, the process of vapor formation begins faster. The liquid with salval salts in it requires a slightly more energy to boil, which in this situation is temperature.

When it is raised to the molecule, which are in salty water, moves much faster, but their number decreases, it means they face less frequently. This can explain the smaller number of steam - after all, its pressure is less than that of fresh water. In order to achieve pressure in the salt water exceeding the atmospheric, and the start of boiling, the temperature is required higher.

Another justification

Many hostesses in cooking are sulking water at the beginning of the process, motivating this by the fact that it will boil faster. And some find an explanation why salty water boils faster, relying on the school knowledge of the physics course, namely the themes concerning the heat transfer. As is known, heat transfer is three types: heat transfer, characteristic of solid bodies, convection, which is present in gaseous and liquid bodies, and radiation.

The last type of heat transfer exists even in space. This is confirmed by the stars and, of course, the sun. But still the main factor in this matter is the density. Since the salty water density is higher than that of fresh, it boils faster. At the same time, for freezing, she needs more time. Consequently, with a more dense fluid, heat transfer will be more active, and boiling will occur faster.

Boiling water under reduced pressure: video

Many hostess trying to speed up the cooking process are sulking water immediately after put the pan on the stove. They are sacred believe that they come correctly, and are ready to lead many arguments in their defense. Is it really and what water boils faster - salty or fresh? To do this, it is quite necessary to put experiments in laboratory conditions, it suffices to dispel the myths that reign in our kitchens with decades with the help of laws of physics and chemistry.

Common myths about boiling water

In the issue of boiling water, people can be divided into two categories. The first are convinced that salt water boils much faster, and the second approval with this absolutely disagree. It is in favor of bringing to the boiling of salt water to be less time, the following arguments are given:

• the density of water in which the salt is dissolved is much higher, therefore the heat transfer from the burner is greater;
• during dissolving in water, the crystalline grille of the table salt is destroyed, which is accompanied by the release of energy. That is, if you add a salt into cold water, the liquid will automatically become warmer.

Those who refute the hypothesis that salty water boils faster, it is argued as follows: during the dissolution of salt in water, the hydration process occurs.

At the molecular level, more strong connections are formed, for the destruction of which more energy is required. Therefore, for boiling salted water requires more time.

Who is right in this dispute, is it really important to salt water at the very beginning of cooking?

Boiling process: Physics "On Fingers"

To figure out what exactly occurs with salty and fresh water when heated, you need to understand what the boiling process is. Regardless of whether the water is salted or not, it boils the same and passes through four stages:

• the formation of small bubbles on the surface;
• an increase in bubbles in the volume and their sedimentation at the bottom of the tank;
• water clouding caused by intense motion of bubbles with air up-down;
• directly the boiling process, when large bubbles rise on the surface of the water and burst with noise, highlighting steam - air, which is inside and heated.

The theory of heat transfer to which the supporters of the solvent of water at the beginning of cooking are appealed, in this case "works", but the effect of water heating due to its density and heat release during the destruction of the crystal lattice is insignificant.

Much more important than the process of hydration, in which sustainable molecular ties are formed.

What they are stronger, the more difficult the air bubble to climb the surface and go down to the bottom of the tank, it takes longer. As a result, if salt is added to the water, the circulation of bubbles with air slows down. Accordingly, salt water boils slower, since molecular ties hold air bubbles in salt water just longer than in fresh.

Solit or not shed? That is the question

Kitchen disputes about which water faster boats salty or unsalted, you can be infinite. As a result, from the point of view of practical application there is no special difference, you sat down the water at the very beginning or after she boiled. Why is it not much important? To understand the situation, you need to refer to physics, which gives exhaustive answers to this, it would seem a difficult question.

It is known that with a standard atmospheric pressure of 760 mm mercury pillar, water boils at 100 degrees Celsius. Temperature parameters may vary under the condition of changes in air density - everyone knows that water boils in the mountains at a lower temperature. Therefore, when it comes to a domestic aspect, in this case such an indicator is much more important as the intensity of the combustion of the gas burner or the degree of heating the electrical kitchen surface.

It is from this that the process of heat exchange is dependent, that is, the rate of heating the water itself. And, accordingly, the time spent on that she boils.

For example, on an open fire, if you try to cook dinner on a fire, the water in the kitel will boil in a matter of minutes due to the fact that the firewood during burning is released more heat than gas in the stove, and the surface heating area is much larger. Therefore, it is absolutely optionally to salt water so that it boils faster - it is enough to turn on the plates to the maximum.

The boiling point of salt water is exactly the same as in fresh, and in distilled. That is, it is 100 degrees under normal atmospheric pressure. But the speed of boiling under equal conditions (for example, if the basis of the usual burner of the gas stove is taken) will differ. In order to boil salted water, it will take more time due to the fact that air bubbles are heavier to break up more durable molecular ties.

By the way, the difference in boiling time exists between tap and distilled water - in the second case, the liquid without impurities and, accordingly, without the "heavy" molecular bonds, will heat up faster.

True, the time difference is only a few seconds that do not make weather in the kitchen and practically no effect on the speed of cooking. Therefore, it is necessary to be guided not by the desire to save time, but the laws of cooking, prescribing to solit each dish at a certain point to preserve and enhance its taste.

Boil is the process of changing the aggregate state of the substance. When we talk about water, we mean a change in liquid state in vapor-shaped. It is important to note that boiling is not evaporation that can occur even at room temperature. Also do not be confused with boiling, which is the process of water heating to a certain temperature. Now, when we sorted out with the concepts, you can determine at what temperature water boils.

Process

The process of converting an aggregate state of liquid into gaseous is complex. And although people do not see this, there are 4 stages:

1. In the first stage, small bubbles are formed at the bottom of the capacitance. You can also notice them on the sides or on the surface of the water. They are formed due to the expansion of air bubbles, which are always in the cracks of the container, where water is heated.
2. In the second stage, the volume of bubbles increases. All of them begin to rush to the surface, since inside them there is a saturated couple, which is lighter than water. With increasing heating temperature, the pressure of bubbles increases, and they are pushed to the surface due to the well-known force of Archimedes. At the same time, you can hear the characteristic sound of boiling, which is formed due to continuous expansion and decrease in the size of bubbles.
3. At the third stage, a large number of bubbles can be seen on the surface. It first creates clouding of water. This process in the people is called "boiling by a white key", and it lasts a short period of time.
4. At the fourth stage, the water is intensively buried, large bursting bubbles arise on the surface, the appearance of splashes. Most often, the splashes mean that the liquid has heated to the maximum temperature. From the water will begin to proceed by steam.

It is known that water boils at a temperature of 100 degrees, which is possible only in the fourth stage.

Para

Couple is one of the water states. When it enters into the air, then, like other gases, has a certain pressure on it. When steaming, the temperature of steam and water remains constant until all fluid changes its aggregate state. This phenomenon can be explained by the fact that when boiling all the energy is spent on the conversion of water into steam.

At the very beginning of the boiling, a wet saturated couple is formed, which after evaporation of the whole liquid becomes dry. If its temperature begins to exceed the temperature of the water, then such steam is overheated, and in its characteristics it will be closer to gas.

Boiling salted water

It is quite interesting to know at what temperature water boils with increased salt content. It is known that it should be higher due to the content in the composition of Na + ions and cl-, which the area occupies between water molecules. This chemical composition of water with salt differs from ordinary fresh liquid.

The fact is that in salty water, the hydration reaction takes place - the process of attaching water molecules to salt ions. The relationship between freshwater molecules is weaker than those formed during hydration, so the boosting of the liquid with a dissolved salt will occur longer. As the temperature grows the temperature of the molecule in water with a salt content is moving faster, but they are becoming less, because of which collisions are carried out less often. As a result, the pair is formed less, and its pressure is due to this lower than the pressure of a couple of fresh water. Consequently, more energy (temperature) will be required for the full vaporization. On average, for boiling one liter of water with a content of 60 grams of salt, it is necessary to raise the degree of boiling water by 10% (that is, 10 s).

Boiling dependence on pressure

It is known that in the mountains, regardless of the chemical composition of the water, the boiling point will be lower. This is due to the fact that the atmospheric pressure is at the height below. Normal is considered to be pressure with a value of 101.325 kPa. With it, the water boiling temperature is 100 degrees Celsius. But if you climb the mountain, where the pressure is an average of 40 kPa, then there the water will boil at 75.88 C. But this does not mean that for the preparation of food in the mountains you will have to spend almost half of the time. For thermal processing of products, a certain temperature is needed.

It is believed that at an altitude of 500 meters above sea level Water will drop at 98.3 s, and at an altitude of 3000 meters the booster temperature will be 90 S.

Note that this law acts in the opposite direction. If you put the liquid into a closed flask, through which steam cannot pass, then with increasing temperature and the formation of a steam, the pressure in this flask will grow, and boiling at elevated pressure will occur at higher temperatures. For example, at a pressure of 490.3 kPa, the water boiling point will be 151 C.

Boiling distilled water

Distilled is the purified water without any impurities. It is often used in medical or technical purposes. With the fact that there are no impurities in such water, it is not used for cooking. It is interesting to note that distilled water boils faster than ordinary fresh, but the boiling point remains the same - 100 degrees. However, the difference in boiling time will be minimal - just a split second.

In kettle

Often people are interested, at what temperature water boils into the kettle, since these devices are used to boil the liquid. Taking into account the fact that the atmospheric pressure in the apartment is equal to the standard, and the water used does not contain salts and other impurities, which should not be there, the booster temperature will also be standard - 100 degrees. But if the water contains salt, the booster temperature, as we already know, will be higher.

Conclusion

Now you know at what temperature water boils, and as atmospheric pressure and the composition of the fluid affect this process. There is nothing complicated in this, and the children get similar information still at school. The main thing is to remember that with a decrease in pressure, the boiling point of the liquid decreases, and it increases with its growth.

On the Internet, you can find many different tables, where the dependence of the boiling temperature of the fluid from atmospheric pressure is indicated. They are available to everyone and are actively used by schoolchildren, students and even teachers in institutions.

Why is it easier to float in salt water than in fresh?

It is easier to swim in salt water than in fresh, because the salt makes the water heavier: if you take two cylinders of the same capacity, in one of which will be salted, and in the other fresh water, the balloon with salt water will weigh a little more. And the more density (weight) of water, the easier it is to swim in it.

The item can float in the fluid if its weight is equal to the weight of the water that he displaces or pushes (the water is displaced in order to give a place). You can look at it on the other side: when you sit in the bath, then you see that the water level in it increases. If you beat the water that your body has crowded, the weight of this water will be equal to the weight of your body. If water has an increased density like salted water, then your body will displace the smaller amount (i.e., in order to equalize your body weight, less water will be required), and you, popping, will find yourself higher than if they surfaced in Freshwater.

In the first glass, ordinary fresh water, in the second - salty,
in the third - very salty.

What is better to keep warm: fresh or salt water?

Two vessels were filled with fresh water. They were heated for about 10 minutes. Then, 2 tablespoons of salt added to one of the vessels and the "salt water" label was placed on it. Under the first attempt, it was not observed a special difference, the temperature was 120 degrees. With a second attempt, 2 more tablespoons of salt added and the difference became noticeable. Salted water cooled significantly faster than ordinary tap water. As part of the experiment, the amount of salt in water was monitored. When the water temperature reached 90 degrees began to collect data. As part of the experiment, the same thermometers were used.

Why water in the ocean salty?

Salt from the surface of the Earth is constantly dissolved and falls into the ocean.
If you dry all the oceans, from the remaining salt it would be possible to build a wall with a height of 230 km and a thickness of almost 2 km. Such a wall could go around the Equator all the globe. Or another comparison. Salt of all dried oceans in terms of volume 15 times the most European continent!
The usual salt is obtained from sea water, salt sources or when developing deposits of stone salt. Sea water contains 3-3.5% salt. The inland seas, such as the Mediterranean Sea, the Red Sea, contain more salt than outdoor seas. Dead Sea, occupying only 728 square meters. km., Contains about 10,523,000,000 tons of salt.
On average, a litter of seawater contains about 30 g of salt. Many millions of years ago as a result of evaporation of seawater were formed in various parts of the Earth. For the formation of a stone salt, it is necessary to evaporate nine ties of the seawater volume; It is believed that in the place of modern deposits of this salt was the inner seas. They evaporated faster than new marine water came - so they appeared the deposits of the stone salt.
The main amount of food salt is mined from a rock salt. Typically, the shafts are paved in salt deposits. Pipes are pumped by clean water, which dissolves salt. By the second pipe, this solution rises to the surface.

Why fresh water boils faster than salty?

Salted water boats at a higher temperature than fresh, respectively, with the same heating conditions, fresh water will boil faster, salt will boil later. There is a whole physico-chemical theory why the situation is so, "on the fingers" this can be explained as follows. Water molecules are associated with salt ions - a hydration process occurs. The connection between water molecules is weaker than the connection formed by hydration. Therefore, the molecule of fresh water is easier (at a lower temperature), it takes away from his "environment" - i.e. Roughly speaking evaporates. And so that the water molecule with the dissolved salt "escaped from the hugs" salt and other water molecules is required more energy, i.e. Big temperature.

Boiling is the process of transition of a substance from liquid into a gaseous state (vaporization in liquid). Boiling is not evaporation: It is characterized by what can happen only under certain pressure and temperature.

Boil - Water heating to boiling point.

Boiling water is a complex process that occurs in four stages. Consider an example of boiling water in an open glass vessel.

In the first stage Boiling water at the bottom of the vessel appear small air bubbles, which can also be seen on the surface of the water on the sides.

These bubbles are formed as a result of expanding small air bubbles, which are in small cracks of the vessel.

In the second stage There is an increase in the volume of bubbles: more and more air bubbles are torn to the surface. Inside bubbles are saturated steam.

As soon as the temperature rises, the pressure of saturated bubbles increases, as a result of which they increase in size. As a result, the force acting on bubbles is strength.

It is due to this force bubbles strive to the surface of the water. If the upper layer of water did not have time to warm up up to 100 degrees with (And this is the boiling point of pure water without impurities), the bubbles are lowered down into a hotter layers, after which they rush back to the surface.

Due to the fact that bubbles are constantly reduced and increased in the amount, sound waves occur inside the vessel, which create noise characteristic to boil.

In the third stage A huge amount of bubbles rises to the surface of the water, which initially causes a slight turbidity of water, which then "pale". This process continues for a long time and has the name "boiling by a white key".

Finally, in the fourth stage Boiling Water begins to raise intensely, large blades appear bubbles and splashes (as a rule, splashes mean that the water is very swapped).

From the water, water vapor begins to form, while water makes specific sounds.

Why "bloom" walls and "cry" windows? Very often the builders are to blame, which incorrectly calculated the dew point. Read the article to find out how important this is a physical phenomenon, and how to get rid of excessive dampness in the house?

What benefit can melt water for wishing to lose weight? You will learn about it, it turns out, you can lose weight without much effort!

Couple temperature when boiling water ^

Couples is a gaseous condition of water. When the pair enters the air, then it, like other gases, has a certain pressure on it.

In the process of vaporization, the temperature of steam and water will remain constant until all the water evaporates. Such a phenomenon is explained by the fact that all the energy (temperature) is aimed at converting water into steam.

In this case, dry saturated steam is formed. Highly dispersed particles of the liquid phase in such a pair are missing. Also couples can be saturated wet and overheated.

Rich steam with suspended highly dispersed particles of liquid phasewhich are evenly distributed over the entire mass of steam, called wet saturated ferry.

At the beginning of the boiling of water, it is such a pair that is then moving into dry saturated. Couples, the temperature of which is larger than the temperature of boiling water, or rather overheated steam, can only be obtained using special equipment. In this case, such a couple will be close in its characteristics to Gas.

Boiling point of salt water ^

The boiling point of salt water exceeds the boiling point of fresh water. Consequently salt water boats fresh fresh. In saline water, there are na + and cl-, which occupy a certain area between water molecules.

In salty water, the water molecules are joined to salt ions - these process is called "hydration". The relationship between water molecules is much weaker than the connection formed during the hydration process.

Therefore, when boiling from fresh water molecules, the vaporization occurs faster.

The boiling of water with a dissolved salt will be required more energy, which in this case appears the temperature.

As the temperature of the molecule in salt water increases, it starts to move faster, but at the same time they are becoming smaller, in view of which they face less often. As a result, less steam is formed, the pressure of which is lower than in a pair of fresh water.

In order for in salted water, the pressure has become above atmospheric and the boiling process has begun, a higher temperature is necessary. When adding 60 grams of salt into water with a volume of 1 liter, the boiling point will increase by 10 C.