Boiling point: features

2024 Author: Erin Ralphs | [email protected]. Last modified: 2024-02-19 11:41

Boiling is a phenomenon that is characteristic of any liquid. It is manifested by the fact that vapor bubbles form 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 is different in different substances. So, the boiling point of engine oil reaches 300-490°C, and for water it is 100°C. This physical quantity depends on several parameters, including boiling conditions and the composition of the substance being heated.

It must be said that the boiling point has certain features. So, 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 indicators.

It should be noted that the temperatureboiling is determined using a special thermometer, which must be immersed in the vapor of the substance, and not in the liquid. In this case, the mercury column is not always completely immersed, 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 of about 26 mm leads to the fact that the boiling point changes by one degree.

How does this indicator help determine the purity of mixtures and solutions? A homogeneous liquid has a constant boiling point. Its change is a sure sign of the presence of impurities that can be isolated during the distillation process, as well as with the help of special devices - dephlegmators.

It is worth noting that in some cases combinations of various substances are specially used. This gives the liquid specific features. So, for example, pure ethylene glycol boils at 197 ° C, and the boiling point of antifreeze is somewhat lower - about 110 ° C.

The transition of liquid to vapor occurs exactly when the appropriate boiling point is reached. In this case, the saturated vapor above the liquid surface has the same numerical value as the external pressure, which leads to the formation of bubbles throughout the entire volume.

It must be said that boiling takes place at the same temperature, but with a decrease or increase in external pressure, its corresponding changes can be observed.

This can explain the phenomenon when food takes longer to cook in the mountains, because at a pressure of about 60kPa, wateralready boils at 85°C. For the same reason, dishes in a pressure cooker cook much faster due to the fact that pressure increases in it, 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 proving important for the distillation of petroleum products to produce purer starting materials.