Boiling point: features

Boiling is a phenomenon that is typical for all 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 differs in different substances. 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 has certain characteristics. 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 point is determined by means of a special thermometer, which must be immersed in vapors of matter, and not into a 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, which can be isolated during the distillation process, as well as with the help of special devices - reflux condensers.

It should be noted that in some cases combinations of various substances are used specifically. This gives the fluid specific features. So, for example, pure ethylene glycol boils at 197 ° C, and the boiling point of tosol is somewhat less - about 110 ° C.

The transition of liquid into vapor occurs precisely 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.

It must be said that boiling takes place 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 food in the mountains is prepared longer, because 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 most 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.