The air we breathe is a highly organized chemical mixture known as the atmosphere. This mixture behaves scientifically as a gaseous solution, meaning one substance is uniformly dispersed throughout another. Applying chemical principles allows us to classify its components based on their relative quantities. Understanding air as a solution provides a framework for identifying which gas acts as the dissolving medium for all the others.
Defining Solutions in Gaseous Mixtures
A solution is defined as a homogeneous mixture where the solute is dissolved completely and evenly into the solvent. While we commonly associate solutions with liquids, the concept applies equally to gases. The solvent is the substance present in the largest amount, providing the bulk medium for the mixture.
The solute is the substance present in a smaller amount that is dispersed into the solvent. This classification by quantity is straightforward in gaseous solutions like air. For air, the gas with the highest concentration automatically fills the role of the solvent, while all other gases are considered solutes.
Nitrogen’s Role as the Atmospheric Solvent
The gas that serves as the solvent in Earth’s atmosphere is molecular Nitrogen (N2). Nitrogen gas makes up approximately 78.08% of the volume of dry air, a concentration significantly higher than any other single component. This overwhelming abundance immediately qualifies Nitrogen as the solvent.
Nitrogen provides the bulk medium in which all the other atmospheric gases are suspended. Nitrogen is also highly unreactive, acting as an inert diluent. This chemical stability means it primarily serves as a background gas, providing physical volume without readily reacting with the solutes. Nitrogen’s role is to dilute more reactive gases, such as Oxygen, and prevent chemical processes like rapid combustion from occurring unchecked.
The Dissolved Gases
The remaining components of air function as the solutes dissolved within the Nitrogen solvent. The primary solute is molecular Oxygen (O2), which accounts for about 20.95% of the atmosphere by volume. This gas is essential for respiration and combustion, and it is evenly distributed throughout the medium.
The next most abundant solute is the noble gas Argon (Ar), present at about 0.93% of the total volume. Beyond these major components, trace gases are also considered solutes:
- Carbon Dioxide
- Neon
- Helium
- Methane