Describe the methods for measuring vapour pressure

Que.: Describe the methods for measuring vapour pressure

Ans.:

Methods for Measuring Vapour Pressure: Vapour pressure of liquids are measured by static and dynamic methods as follows:

1. Static method:

This is a simple method for determination of vapour pressure. A sufficient amount of liquid whose vapour pressure is to be determined is placed in the bulb connected to a mercury manometer and a vacuum pump. All the air from the bulb is removed with the help of the vacuum pump and the stop cock is closed. A part of the liquid evaporates. The system is then maintained at a fixed temperature for enough time for equilibrium. The difference in the levels of mercury in the manometer is equal to the vapour pressure of the liquid.

Dynamic Method:

An inert gas is passed through a given liquid at a constant temperature (T). The gas saturated with the vapour of the liquid leaves the flask at the exit tube. This method is particularly useful for liquids of low vapour pressure.

Que.: Describe the methods for measuring vapour pressure