Vapor pressure of a liquid is the maximum pressure exerted by its vapors, when the dynamic balance between the liquid and gas phases is reached.
Let's assume you have a non-volatile substance dissolved in a volatile solvent, eg water and salt. Will this liquid behave as if it were in its pure state? In this case, pure water would have a higher maximum vaporization voltage, do you know why? A liquid being pure evaporates more easily.
Suppose the amount of salt dissolved in the above solution is 10%, we know that salt is not volatile and therefore the exerted tension is exclusively water, but necessarily water vapor. The 10% salt present in the solution prevents the vaporization of the liquid from being fast, it is then determined that this maximum vapor pressure is 10% lower than that of pure water.
The property that studies this lowering of the maximum vapor pressure caused by the addition of a solute is called Tonoscopy.
By Líria Alves
Graduated in Chemistry
Brazil School Team
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Source: Brazil School - https://brasilescola.uol.com.br/quimica/pressao-vapor-solucoes.htm