What is the partial pressure of oxygen in air at atmospheric pressure (1 atm)? Assume ideal behavior.

Express your answer to two decimal places and include the appropriate units.

The ideal gas law, PV = nRT is independent of the kind of gas. In other words, the pressure exerted by a given number of ideal gas particles is the same whether the sample consists of all one type of particle or a mixture of different kinds of particles.

Therefore, the pressure exerted by a mixture of gases can be expressed as follows:

${\mathbf{P}}_{\mathbf{total}}\mathbf{=}\frac{({n}_{1}+{n}_{2}+{n}_{3}+...)\mathbf{RT}}{\mathbf{V}}\mathbf{=}\frac{{\mathbf{n}}_{\mathbf{total}}\mathbf{RT}}{\mathbf{V}}$

A *partial pressure* is the pressure exerted by just one type of gas in a mixture. A partial pressure is calculated using only the number of moles of that particular gas, instead of the total number of moles:

${\mathbf{P}}_{\mathbf{1}}\mathbf{=}\frac{{\mathbf{n}}_{\mathbf{1}}\mathbf{RT}}{\mathbf{V}}\mathbf{,}\mathbf{}{\mathbf{P}}_{\mathbf{2}}\mathbf{=}\frac{{\mathbf{n}}_{\mathbf{2}}\mathbf{RT}}{\mathbf{V}}\mathbf{,}\mathbf{}{\mathbf{P}}_{\mathbf{3}}\mathbf{=}\frac{{\mathbf{n}}_{\mathbf{3}}\mathbf{RT}}{\mathbf{V}}\mathbf{,}\mathbf{}\mathbf{etc}\mathbf{.}$

The sum of the partial pressures is equal to the total pressure in the mixture:

${\mathbf{P}}_{\mathbf{total}}\mathbf{=}{\mathbf{P}}_{\mathbf{1}}\mathbf{+}{\mathbf{P}}_{\mathbf{2}}\mathbf{+}{\mathbf{P}}_{\mathbf{3}}\mathbf{+}\mathbf{.}\mathbf{.}\mathbf{.}$

Air is about 78.0% nitrogen molecules and 21.0% oxygen molecules. Several other gases make up the remaining 1% of air molecules.

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