manometric method.pptx

manometric method

1. Manometric Method 1 The liquid whose vapour pressure is to be determined is taken in flask placed in the thermostat. One end of the tube from flask is connected to manometer and other end is connected to vacuum pump . The air above the liquid is removed in the following steps. Freezing: The liquid is frozen with the help of freezing mixture and space above the liquid is evacuated. In this way, air is removed from the surface of liquid along with the vapours of liquid. Melting: The frozen liquid is melted to release entrapped air. Re-freezing: Liquid is again frozen and released air is evacuated. This process is repeated many times till almost all the air is removed.

2. Measurement of vapour pressure 2 The liquid in the flask is warmed in thermostat at a temperature at which vapour pressure is to be determined. Difference in the heights of Hg column in two limbs of manometer determines the vapour pressure of liquid. The pressure on the surface of liquid is equal to sum of atmospheric pressure and vapour pressure of liquid. That is the reason why column of manometer facing the liquid is more depressed than facing the atmosphere. The vapour pressure of liquid is given by following equation. P = P a +  h P = vapour pressure of liquid at one atmosphere. P a = atmospheric pressure  h = difference in the heights of Hg column in two limbs of manometer. It gives us the vapour pressure of liquid.