Question

Why should the Barometric Pressure be corrected for the vapor pressure of water?

Answer 1

Barometric Pressure:

1. Atmospheric pressure is the measure of air pressure in the atmosphere.
2. It is measured using a device called barometer, therefore also called as barometric pressure.
3. Its unit is pascals (Pa).

Water Displacement Method:

1. Sometimes while doing laboratory experiments, the gas evolving in a reaction needs to be collected. This gas is collected through water displacement method.
2. In this there are 2 containers, one in which the reaction takes place and other which is used for gas collection. The other container is filled with water and kept inverted in a water reservoir. The gas is collected using a hose. With the creation of gas, there is displacement in water too.

Water Vapour Pressure Correction:

1. The pressure is partially due to gas and partially due to water vapour that escaped from jar due to water surface.
2. So, in order to determine the pressure of the gas, the water pressure must be subtracted from the total water vapour pressure, the formula for this is expressed as, $P_{gas}=P_{total}-P_{H_{2}O}$.

Hence, the Barometric Pressure is corrected for the vapour pressure of water.