Daltons Law  

When a gas is collected from a chemical reaction, many times it is collected by a process called water displacement. If we want to know the pressure exerted by the gas alone, we must remove the pressure exerted by the water. The water pressure is a function of its temperature. Daltons Law states that the total pressure in a container is the sum of the partial pressures of all the gases in the container. So we must remove the pressure of the water vapor. We can also determine the volume of a dry gas by removing the effect of water.

