Vapour pressure of gasses collected over water.
During an experiment,one may opt to collect a gas over water, however there is variation on pressure as shown;
When the level of water in the gas jar is equal to the level of water outside the gas jar, the pressure insides the gas jar is equal to the atmospheric pressure. This is illustrated by the following diagram;
A factor to consider when determining the vapour pressure of gasses collected over water is the vapour pressure of water itself.This pressure is present since water is continually everporating.
Considering the level of water when the gas jar is equal with the level of water in the trough; the dry gas pressure is found by;
Dry gas vapour pressure = Total vapour pressure - Vapour pressure of water
During a reaction,0.15L of nitrogen gas was produced at a temperature of 230C and pressure of 760torr.What the partial pressure of nitrogen gas?
Vapour pressure of nitrogen = Total vapour pressure - The Vapour pressure of water
From the standard table, the vapour pressure of water when the temperature is 230C is 21.1torr
Because we had been given the pressure of the system,i.e 760torr;
Vapour pressure of nitrogen is thus;
760torr - 21.1torr = 738.9torr