Boiling point: features

Boiling is a phenomenon that is characteristic ofany liquids. It is manifested by the formation of vapor bubbles throughout the solution. It should be noted that boiling is observed only at a certain temperature and depends on the type of substance. This indicator is an important characteristic. It can be used to separate liquid compounds, as well as to determine their purity.

This indicator in various substancesis different. Thus, the boiling point of the engine oil reaches 300-490 ° C, and for water it is 100 ° C. This physical value depends on several parameters, including the boiling conditions and the composition of the substance that is heated.

It must be said that the boiling point hascertain features. Thus, a vapor pressure is created on the surface of the liquid, which is formed rather slowly in the presence of a free surface. If we are talking about the middle of the medium, then it can be heated much more than when boiling. This explains the phenomenon of "overheating", in which the liquid does not boil, but is characterized by high temperature indices.

It should be noted that the boiling pointis determined by means of a special thermometer, which must be immersed in the vapors of the substance, and not into the liquid. In this case, the mercury column can not always be loaded completely, so you need to take into account the correction of the thermometer. For different liquids this value is different. On average, it is believed that a change in atmospheric pressure by about 26 mm causes the boiling point to change by one degree.

How does this indicator help?to determine the purity of mixtures and solutions? Homogeneous liquid is characterized by a constant boiling point. Its change is a sure sign of the presence of extraneous impurities that can be isolated during the distillation process, and also with the help of special devices - reflux condensers.

It is worth noting that in some casescombinations of various substances are specially used. This gives the fluid specific characteristics. For example, pure ethylene glycol boils at 197 ° C, and the boiling point of the antifreeze is somewhat less - about 110 ° C.

The transition of the liquid into vapor occurs precisely when,when the corresponding boiling point is reached. The saturated vapor above the surface of the liquid has the same numerical value with the external pressure, which leads to the formation of bubbles throughout the volume.

I must say that boiling is at the same temperature, but with a decrease or increase in the external pressure, one can observe its corresponding changes.

This can explain the phenomenon when eating in the mountainsis prepared longer, since at a pressure of about 60 kPa water boils already at 85 ° C. For the same reason, the dishes in the pressure cooker are prepared much faster due to the fact that the pressure in it increases, and this leads to a concomitant increase in the temperature of the boiling liquid.

It should be noted that boiling is the mosta common method of physical disinfection. Without this process, it is impossible to cook any dish. It is also important for refining petroleum products in order to obtain cleaner starting materials.