Is Air a Pure Substance? (+ 3 More Things to Know)

No, air is not considered a pure substance. Air is a mixture of different gases, primarily nitrogen (approximately 78%), oxygen (approximately 21%), and small amounts of other gases such as carbon dioxide, argon, and trace gases. ¹

Well, this was just a simple answer. But there are few more things to know about this topic which will make your concept super clear.

So let’s dive right into it.

Why is air not a pure substance?

Air is not a pure substance because it is a mixture of several different gases and particles. The primary components of air are nitrogen, oxygen, and traces of other gases such as carbon dioxide, argon, and water vapor. These gases exist together in varying proportions, depending on factors such as location, altitude, and pollution levels. ²

The presence of different gases in air means that its composition can vary from one place to another. For example, air in a heavily industrialized area might contain higher levels of pollutants, while air in a rural or remote location might be cleaner and have different proportions of gases.

Additionally, air can also contain suspended particles like dust, pollen, and pollutants, which further indicates that it is a mixture. ³

The uniform mixture of gases and particles in air makes it a homogeneous mixture rather than a pure substance. A pure substance, by definition, consists of only one type of element or compound. ⁴

While the individual gases in air can be considered pure substances, the combination of these gases and particles creates a mixture with varying compositions.

Why is air a mixture?

Air is considered a mixture because it is composed of multiple substances that are physically combined but can be separated by various means. In the case of air, it is primarily a mixture of gases, although it can also contain suspended particles.

Here are some reasons why air is classified as a mixture:

• Composition: Air is made up of different gases such as nitrogen, oxygen, carbon dioxide, argon, and trace amounts of other gases. Each of these gases retains its individual properties within the mixture.
• Varying Proportions: The proportions of gases in the air can vary depending on several factors such as location, altitude, and atmospheric conditions. For example, the proportions of oxygen and carbon dioxide in the air differ at sea level compared to high altitudes. These variations in proportions further support the classification of air as a mixture.
• Homogeneity: Although air may appear uniform and homogeneous to our senses, it is not chemically combined at the molecular level. The gases in air do not chemically react with each other, and they retain their distinct properties and behavior. This is a characteristic feature of mixtures.
• Separation: The components of air can be separated by physical means. For instance, techniques like fractional distillation can be employed to separate the different gases present in air based on their boiling points. ^{5 6} This ability to separate the components further supports the classification of air as a mixture.

Overall, the presence of multiple gases with varying proportions and the ability to separate them indicate that air is a mixture rather than a pure substance.

Is air a homogeneous or heterogeneous mixture?

Air is generally considered a homogeneous mixture. ⁷ While it may contain different gases and suspended particles, they are uniformly distributed throughout the atmosphere on a macroscopic scale. This means that air appears to be the same regardless of the location or specific sample taken.

Even though air may contain varying proportions of gases and particles in different areas or under specific conditions, these variations are often at a microscopic or localized level and not readily discernible to the naked eye. The overall composition of air remains fairly consistent and uniform.

It’s important to note that while air is considered a homogeneous mixture on a macroscopic scale, there can be variations in air quality due to pollution, particulate matter, or localized sources of contamination.

However, these variations generally do not change the overall classification of air as a homogeneous mixture.

Further reading

Why is Table Salt a Pure Substance?
Why is Silicon a Metalloid?
Is Sulfur a Metal?
Is Aluminum a Transition Metal?
Is Aluminum a Metal, Nonmetal or Metalloid? 

1. Climate Change, N. G. (2016, September 12). 10 interesting things about air – Climate Change: Vital Signs of the Planet. Climate Change: Vital Signs of the Planet. https://climate.nasa.gov/news/2491/10-interesting-things-about-air
2. for Science Education, U. C. (n.d.). What’s in the Air? | Center for Science Education. What’s in the Air? | Center for Science Education. https://scied.ucar.edu/learning-zone/air-quality/whats-in-the-air
3. Air Pollution | Effective Health Care (EHC) Program. (n.d.). Air Pollution | Effective Health Care (EHC) Program. https://effectivehealthcare.ahrq.gov/health-topics/air-pollution
4. Kinds of Matter. (n.d.). Kinds of Matter. http://www.chem.uiuc.edu/rogers/Text1/Tx12/tx12.html
5. Air separation – Wikipedia. (2022, November 30). Air Separation – Wikipedia. https://en.wikipedia.org/wiki/Air_separation
6. Oliver-Hoyo, M., Switzer, W. L., & Robert Eierman. (2005, February). Fractional Distillation of Air and Other Demonstrations with Condensed Gases. Journal of Chemical Education, 82(2), 251. https://doi.org/10.1021/ed082p251
7. Paterson, D. (2018, April 16). Mixtures and solutions. RSC Education. https://edu.rsc.org/cpd/mixtures-and-solutions/3008735.article