Boil water in an iron pot, the water reaches a certain temperature, and before it reaches the boilin

When we boil water in a kettle or pot, we will always see that there will be many small bubbles on the wall of the kettle or pot before the water boils, and these situations will continue to increase with the increase of water temperature, and the water surface will basically be completely eliminated before the critical boiling. Does anyone know what gas these bubbles are?

When we were in junior high school, we learned from books that when water boils, it produces a lot of water vapor, and we see that when it boils, it constantly comes out of the water of different sizes, and then it bursts to the surface, and the splash is formed. So are the bubbles produced by water before boiling and bubbles produced when boiling the same gas?

The answer is no.

We can see from observation that the bubbles produced by the boiling water are basically directly generated in the water that is not next to the wall of the container, and there are no bubbles on the wall of the container. As for the bubbles that are produced before the water boils, it is the exact opposite. Therefore, the bubbles produced when the water is boiling are almost all the phenomenon that the water is directly heated at the bottom of the container and becomes water vapor as soon as it comes out of the water surface.

However, water is different before boiling, at that time the water and the container have just been heated, and have not yet reached the extent that a large number of water molecules are immediately vaporized, and the bubbles produced at this time are basically the air dissolved in the water, because the air that can be dissolved in the water is reduced when the water is heated, so the air is constantly precipitated out of the water, and the container wall is the place where the heat conduction is the fastest, and it is generally the first place to be heated, so the water is generally the first bubble on the container wall before boiling.

In the same way, in life and industry, many liquids will precipitate solid and gaseous substances due to temperature changes, especially in industry, many solutions precipitate gaseous substances due to temperature changes are toxic, so we should be more careful and detect more at this time.

That bubble is air, and as the temperature rises, the air that was originally dissolved in the water precipitates out to form bubbles.

When water is exposed to high temperatures, it will change from liquid to gaseous state, and due to the continuous accumulation of heat, the bottom part of the water vaporizes relatively quickly, and the temperature of the water half part is lower than that below, and bubbles will be generated. When the temperature at the bottom of the water rises, the heat will rise, and a large number of bubbles will be produced at the same time, and the part of the bottom of the water that contacts will produce a sound due to the temperature difference, at this time, the inside of the water is also constantly tumbling, the water temperature of the upper part is relatively low, at this time, it will circulate downward, and there are a large number of bubbles gushing out, and there will be a sound. When the upper and lower water temperatures reach the same temperature, the water just circulates up and down without bubbles, and the bottom of the pot and the water temperature are the same, so you can't hear too much noise.

Hope it helps, thank you.

When heating cold water, when the temperature has not reached the boiling point, bubbles often emerge in the water, because with the increase of the temperature of the cracking delay, the solubility of the gas originally dissolved in the water decreases, so bubbles escape

Therefore, the answer is: the solubility of the gas decreases with the increase of temperature, and the solubility of the gas decreases with the increase of temperature

It's because of the solubility of the water, when it's cold, it's dissolved in it, it's dissolved in it, carbon dioxide, and so on, and when the temperature rises, the solubility decreases, and the gases in the water quickly saturate, and it's forced out of the water, which is why when you boil water (before it boils) you see the bottom of the water (the bottom of the pot). The bottom of the pot and so on) will bubble up for a reason, which is the most basic knowledge of chemistry in the third year of high school

Before boiling, the temperature of each layer in the window is different, the temperature of the water layer near the heating surface is higher, and the temperature near the water surface is lower. The bubble not only has the air pressure p. inside the bubble during the ascent processWith the decrease of water temperature and decrease, there is a part of the water vapor in the bubble condensed into saturated steam, the pressure is also decreasing, and the external pressure is basically unchanged, at this time, the external pressure of the bubble is stronger than the internal pressure, therefore, the volume of the bubbles on the rise will shrink in the process, when the water temperature is close to the boiling point, a large number of bubbles emerge, rising one after another, and quickly from large to small, so that the water oscillates violently, generated"The ruler is hum, hum"This is it"The water does not boil"The truth.

Before boiling: the main reason.

In the process of bubble rising, the water below is heated first, and the temperature rises, so a part of the water vaporizes into water vapor to form bubbles, and the buoyancy of the bubbles is greater than its own gravity, causing the bubbles to rise. And because water is a bad conductor of heat, the water temperature of the lower part rises, and the water temperature of the upper part is still low, in the process of bubble rising, the bubble encounters cold water with a lower temperature than it, and a part of the water vapor will be exothermic and liquefied into small water droplets, and the mass of the bubble will become smaller, so the volume of the bubble will be correspondingly smaller.

Secondary causes. Since the internal pressure of the liquid increases with the increase of depth, when the bubble rises, the external pressure of the bubble becomes smaller and the volume of the bubble becomes larger.

When boiling: the main cause.

Due to convection, the temperature of the upper and lower parts of the water reaches the boiling point, and the heating continues, and as before the water boils, there is water vaporization into water vapor to form bubbles to rise. In the process of rising, water vaporization into water vapor is also continuous, so many bubbles gather together and accumulate more and more, so that their volume increases.

Secondary causes. As it rises, the depth of the bubble decreases, which also increases its volume. The effect of these two aspects is the same, and the final phenomenon is that the bubble becomes larger and larger.

First of all, before the water boils, the bubbles at the bottom will gradually shrink during the rise, and after boiling, the bubbles will gradually become larger.

The question of bubbles before and after boiling water is strictly a bit complicated. I explained according to the knowledge within the scope of junior high school and my own understanding, which may be different from the facts, and the best way to verify this is to prepare a laboratory thermometer and observe while heating (I did not do this experiment): note at a standard atmospheric pressure.

1.The initial bubble is the precipitation of the gas dissolved in the water when the temperature becomes high, and the temperature does not need to be too high, 40 or even lower. (In summer, you can see the side wall of the bottled mineral water container at home).

2.If the precipitated gas is removed and the observation continues, when it is heated to about 90, the temperature at the bottom of the container may reach the boiling point and continue to heat due to uneven heating. The bottom part of the water boils to produce large bubbles (water vapor).

However, during the ascent, the upper water quickly liquefies the water vapor in the bubble, and the bubble becomes smaller and disappears. This phenomenon is more noticeable when the metal container is heated, where the bubbles bulge at the bottom of the container and then disappear quickly.

3.Finally, when the boiling point is reached and can continue to absorb heat, the bubble changes from large to large (from small to large). Reach the surface of the water and rupture. At standard atmospheric pressure, 100 at this time

At a normal temperature, water can only produce fewer and smaller bubbles, while when the temperature reaches its boiling point, the water will vaporize violently, producing a large number of bubbles.

When the temperature of the water reaches its boiling point, it boils and a large number of bubbles begin to be produced.

There are some gases dissolved in the water, and when heated, the reduced solubility of the gases escapes from the water.

There are always some gases such as air dissolved in water, and when cold water is heated, the temperature increases, and the solubility of the gas decreases, so bubbles often bubble out even if the boiling point has not yet been reached.

It's because of solubility.

When the water is cold, oxygen is dissolved in it.

carbon dioxide and so on.

When the temperature increases, the solubility decreases.

The gases in the water quickly saturate.

And was "forced out" of the water.

That's why when you boil water (before it boils) you see the bottom of the water (the bottom of the pot). The bottom of the pot and so on) will bubble up.

Reason. This is the most basic knowledge of Gao Cong Chemistry Before boiling, the temperature of each water layer in the window is different, the temperature of the water layer near the heating surface is higher, and the temperature near the water surface is lower. The bubble not only has the air pressure p. inside the bubble during the ascent process

As the water temperature decreases, a part of the water vapor in the bubble condenses into saturated steam.

The pressure is also decreasing, and the external pressure is basically unchanged, at this time, the external pressure of the bubble is stronger than the internal pressure, so the volume of the bubbles floating in the rising process will shrink, when the water temperature is close to the boiling point, a large number of bubbles emerge, rising one after another, and rapidly from large to small, so that the water oscillates violently, generated"Buzz, buzz"This is it"Ringing water.

No, it doesn't open"The truth.