Gases - Chemistry - page 253

Example 2
A mixture of two gases exerts a total pressure of 142.5 kPa. If the
partial pressure exerted by one of the gases is 96.4 kPa, what is the
partial pressure exerted by the other gas?
P 2 = P total - P 1 = 142.5 kPa - 96.4 kPa = 46.1 kPa
A variation on this type of problem involves making use of the molar
ratio of the gases in the mixture. Take a look at Example 3.
Example 3
A mixture made up of 2.0 moles of nitrogen gas and 3.0 moles of
hydrogen gas exerts a total pressure of 4.0 atm. What is the partial
pressure exerted by the hydrogen gas?
As you can see, the gas is made up of 3.0 parts (moles) hydrogen and
2.0 parts nitrogen. The gas is then made up of 60% hydrogen, and there-
fore hydrogen is responsible for 60% of the total pressure exerted by the
gas. Here is the work:.
pressure of hydrogen = total pressure × % of mixture that is hydrogen
= 4.0 atm × 60%
= 4.0 atm × .60
= 2.4 atm
Another variation of this type of problem that you are likely to en-
counter involves mathematically removing the water vapor pressure from
a sample of gas, in order to determine the pressure exerted by a dry gas. In
the laboratory, you may collect a sample of a gas by bubbling it through a
column of water. The resultant gas will be a mixture of the water vapor and
whatever gaseous product that you intended to collect. In order to subtract
out the water vapor pressure, you must determine the temperature of the
gas sample, and then refer to a table such as the one shown on page 271.