Nitrogen gas (\(N_2\)) is the most abundant component of Earth’s atmosphere. This colorless, odorless diatomic molecule is fundamental to our environment, but whether it constitutes a “solution” is nuanced. The answer depends entirely on the physical state of the substances mixed with it. Scientifically, \(N_2\) can be both a component of a solution and the primary medium for one.
Defining the Components of a Solution
A solution is a homogeneous mixture where components are uniformly distributed at a molecular level, creating a single phase. Solutions are composed of two parts: a solute and a solvent.
The solvent is the substance present in the greatest quantity, acting as the dissolving medium. Conversely, the solute is the substance dissolved in the solvent, typically present in a lesser amount. For example, in saltwater, water is the solvent and salt is the solute. This framework applies to mixtures of gases, liquids, and solids.
Nitrogen Gas as a Solute in Liquids
Nitrogen acts as a solute when it dissolves into a liquid, such as water or blood. Its nonpolar nature and triple bond make it relatively unreactive and sparingly soluble in polar solvents like water. Consequently, the solubility of nitrogen gas in water at standard temperature and pressure is low.
The most relevant example of \(N_2\) as a solute is its presence in human blood plasma. Even at normal atmospheric pressure, a small, equilibrium amount of nitrogen is dissolved in the bloodstream. The solubility of \(N_2\) in blood at body temperature (\(37^\circ\text{C}\)) is approximately \(1.90\text{ mL}\) of gas per deciliter of blood at one atmosphere of pressure.
This dissolved nitrogen becomes a consideration in hyperbaric environments, such as during deep-sea diving. According to Henry’s Law, the amount of gas dissolved in a liquid is directly proportional to the partial pressure of that gas above the liquid. As a diver descends, the increased pressure causes significantly more \(N_2\) to dissolve in the blood and tissues.
If the pressure is reduced too quickly upon ascent, the dissolved nitrogen gas comes out of solution rapidly, forming bubbles in the bloodstream and tissues. This process causes decompression sickness, commonly known as “the bends.” While \(N_2\) is present in blood, it is far less soluble than other gases like carbon dioxide, which has specialized transport mechanisms in the body beyond simple dissolution.
Nitrogen as a Component in Gaseous Mixtures
The most common context for nitrogen gas in a solution is as a component of the atmosphere. Air is a textbook example of a gaseous solution, where various gases are mixed thoroughly and uniformly. Gaseous solutions are unique because all gases mix completely with one another, forming homogeneous mixtures regardless of the proportions.
In the atmosphere, nitrogen gas makes up approximately \(78\%\) of the volume of dry air. Since the solvent is defined as the component present in the greatest amount, \(N_2\) functions as the solvent in this enormous gaseous solution. Oxygen (\(O_2\)), which makes up about \(21\%\), and trace gases like argon and carbon dioxide, are the solutes dissolved within the nitrogen.
This uniform mixture of \(N_2\) and other gases extends throughout the atmosphere, creating a single, gaseous phase. The constant, random motion of gas molecules ensures the homogeneity of the mixture, thereby meeting the requirement for a solution. The stability and uniformity of the air we breathe confirm that in its primary real-world context, nitrogen gas is the major constituent of a vast gaseous solution.