Dalton’s Law of Partial Pressures
When a Gas Is Made Up of a Mixture of Different Gases, the Total Pressure
of the Mixture Is Equal to the Sum of the Partial Pressures of the
Components; That Is, the Partial Pressure of the Gas Would Be the Pressure
of the Individual Gas If It Alone Occupied the Volume. The Formula Is:Ptotal = Pgas 1 + Pgas 2 + Pgas 3 + ...TIP
Know Dalton’s Law of Partial Pressures.Type Problem
A mixture of gases at 760. mm Hg pressure contains 65.0% nitrogen, 15.0%
oxygen, and 20.0% carbon dioxide by volume. What is the partial pressure of
each gas?
If the pressure was given as 1.0 atm, you would substitute 1.0 atm for- mm Hg. The answers would be:
Corrections of Pressure
CORRECTION OF PRESSURE WHEN A GAS IS COLLECTED OVER
WATER. When a gas is collected over a volatile liquid, such as water, some of
the water vapor is present in the gas and contributes to the total pressure.
Assuming that the gas is saturated with water vapor at the given temperature, you
can find the partial pressure due to the water vapor in a table of such water vapor
values. This vapor pressure, which depends only on the temperature, must be
subtracted from the total pressure to find the partial pressure of the gas being
measured.