Nitrogen gas (N2), which makes up about 78% of Earth’s atmosphere, is an inert, colorless, and odorless diatomic molecule. Factually, nitrogen does not chemically absorb moisture; it is non-hygroscopic. It lacks the physical and chemical properties needed to bind water molecules. While water vapor can exist alongside nitrogen gas, the nitrogen molecules themselves do not attract or incorporate the water.
Why Nitrogen Does Not Absorb Water
The inability of nitrogen to absorb water is rooted in its molecular structure and resulting lack of polarity. The molecule is composed of two nitrogen atoms connected by a very strong triple covalent bond. This bond gives the gas a highly stable and unreactive character.
Because the two atoms in the N2 molecule are identical, they share the electrons perfectly evenly, resulting in a non-polar structure with no net electrical charge separation. Water (H2O), in contrast, is a highly polar molecule, meaning it has a partial positive charge near the hydrogen atoms and a partial negative charge near the oxygen atom.
Chemical absorption requires a significant electrical attraction between molecules, such as the dipole-dipole forces found in polar compounds. Since the non-polar nitrogen molecule lacks these attractive charges, it does not form strong bonds with polar water molecules. Nitrogen prefers to interact only weakly with other molecules, including water.
While nitrogen is not chemically absorbed, its solubility in water is extremely low. This minimal dissolution is due to very weak, temporary forces called London dispersion forces. These forces allow for slight mixing but are not considered true chemical absorption. For practical purposes, nitrogen gas is correctly described as non-absorbent and inert toward moisture.
Using Nitrogen to Manage Humidity and Oxidation
The inert, non-reactive nature of nitrogen makes it extremely valuable for managing humidity and preventing oxidation in many industrial and commercial applications. It is frequently used as a “purging” or “blanketing” gas. This process involves intentionally flooding an enclosed space with nitrogen to displace air containing oxygen and water vapor.
Water vapor acts as a catalyst in degradation processes, including oxidation and corrosion. Introducing nitrogen creates an ultra-low-humidity, oxygen-free environment that effectively stops these reactions. For example, nitrogen is flushed into electronic dry cabinets to remove moisture-laden air, protecting sensitive components like printed circuit boards from corrosion.
In food packaging, nitrogen is used to displace oxygen, which causes spoilage and rancidity. The dryness of the nitrogen source is important; industrial-grade nitrogen typically has an extremely low dew point, meaning it is virtually moisture-free.
The primary function of nitrogen in these applications is not to absorb water, but to physically push the moist air out of the system. This displacement prevents the harmful interaction of oxygen, moisture, and the protected material. This principle is also used in vehicle tires, where dry nitrogen helps maintain consistent pressure and reduces the risk of rim corrosion.