About humidity.

A: Absolute humidity φ: At a certain temperature, the actual content of water vapor in the sample air is called absolute humidity.

B: Saturation humidity φ: at a certain temperature, the maximum amount of water vapor that can be contained in the sample air (beyond this amount, condensation will occur and water droplets will appear on the wall), which is called saturation humidity.

Saturated humidity and absolute humidity are related to the number of samples and usually have no practical significance, so relative humidity is introduced.

C: Relative humidity α: the ratio of the absolute humidity of a sample at a certain temperature to the saturated humidity at that temperature (which is independent of the number of samples and can objectively measure humidity), and is defined as relative humidity.

α

=

(φ/Φ)× 100%

1、α

=0, the air is completely dry and contains no water.

2、α

= 100%, saturated.

The water content in the air is related to the temperature. The higher the temperature, the more water vapor it can hold.

The percentage of the vapor pressure of water in the air at a certain temperature and the saturated pressure of water vapor at the same temperature is called the relative humidity of the air at that time.

Answer the latter question first and empty the air in the closed container. The relative humidity above the water surface is 100%.

If the solute is dissolved in water, the humidity of its vapor will decrease, because the solute molecules occupy a part of the surface of the solution, so the solvent molecules escaping from the liquid surface in unit time will decrease accordingly. When equilibrium is reached, the vapor pressure of the solution must be the vapor pressure of the pure solvent.

At a certain temperature, the vapor pressure of dilute solution is equal to the product of the vapor pressure of pure solvent and the molar fraction of solvent. But this is only applicable to dilute solution, and the vapor pressure of this concentrated solution of lithium chloride can only be measured by experiments.

In order to obtain the required relative humidity, a solution with a vapor pressure close to the required vapor pressure can be used. Why use saturated solution here? Because when the saturated solution evaporates steam, the solute in the solution also precipitates, and the concentration of the solution remains unchanged, thus ensuring the stability of relative humidity.

This method generally uses salt solution because salt is not volatile, but the relative humidity of salt solution, especially concentrated salt solution, can only be measured because of its complexity. It is difficult to calculate accurately.