Air is everywhere. Even if you cannot see it or hold it, it is all around you. You breathe air in and out, and without air, human beings cannot stay alive. Did it ever cross your mind what is air? Is air an element or compound? What about a compound or a mixture? This had been the most confusing question in the 6th standard science textbook and is still unclear to most of us. So, is air an element, compound, or mixture? Let’s find out!
1. What is Air?
Before coming to the topic of air being an element or compound, let’s get some definitions of air in different fields.
- Chemistry: Air is a colloidal suspension of gases that forms a layer of thick gaseous cover on Earth, mainly oxygen and nitrogen.
- Geography: Air is the mixture of gases that forms the Earth’s atmosphere. This atmosphere is the protective layer for Earth to retain its habitable conditions for life to thrive on the surface. Also, check out what makes up the Lithosphere?
- Physics: Air results from the Earth’s gravitational pull on the gaseous molecules surrounding the planet. The layer of air is more concentrated closer to the Earth’s surface, making a blanket of a gaseous refractive layer. This layer prevents the entry of harmful cosmic radiations into the atmosphere and holds surface warmth inside the blanket.
2. What are the Components of Air?
From the definitions above, it must be quite clear that air is a mixture of gases. The mixture has more than 99% of nitrogen (N2), oxygen (O2), carbon dioxide (CO2), and water vapor (H2O). The rest 1% consists of inert gases like ozone (O3), argon (Ar), helium (He), neon (Ne), methane (CH4), and other pollutant gases found in traces. (See What are Examples of Elements in Everyday Life?)
3. What is Air Composition and Molecular Weight?
Air is dominantly composed of nitrogen (~78%) and oxygen (~21%). Though in traces, several heavy gases give pure air its heavy molecular weight. The exact molecular weight of pure or dry air is 28.97 grams per mole. The presence of water vapor in the air on a humid day makes it lighter. Therefore, on a hot and humid day, air pressure is less than on other dry days, and the air’s molecular weight falls. (See How many valence electrons does oxygen have?)
4. Is Air an Element?
After discussing air and its composition, we are back to the question; is air an element? An element is a pure substance that occurs naturally in its original state. The components of air, like nitrogen or oxygen, are elements by themselves because they exist in the atmosphere in their pure state.
Metals like aluminum and iron are elements that have to be extracted from their naturally occurring ores. There is no such element as air. Air is a mixture of all the gaseous elements and compounds found in the Earth’s atmosphere and, therefore, not an element. (See What is the Main Source of Water?)
5. Is Air a Compound?
You may also ask, is air an element or compound? You already know that air is not an element, even though the air is not a compound. The basic difference between a compound and an element is that a compound is a chemical substance formed by the chemical reaction of two or more elements.
A compound is technically a pure substance with a fixed chemical composition throughout with a molecular formula and molecular weight. Compounds are also present in the air, carbon dioxide, water vapor, methane, and sulfur dioxide (an air pollutant). So, the air is not a compound. Also, check out what are Rubies made of?
6. Is Air a Mixture or Solution?
With this question, you have come to the solution. Yes, the air is a mixture of both gaseous elements and compounds which exists in the state of a gaseous colloidal solution in the atmosphere.
A solution is a homogenous mixture of elements and compounds, while a mixture might not be homogenous necessarily. Though the properties of air are the same almost everywhere, it is not evenly distributed in the atmosphere. The compositions of the air vary from place to place and time to time. Therefore, it can be concluded that air is a mixture. (See Why do atoms form chemical bonds?)
7. Is Air a Mixture or a Colloid?
Air is primarily a mixture of gases, liquids, and solid dust particles. The basic difference between a colloid and a suspension is the size of particles dissolved.
- When the air is pure, it is simply a gaseous mixture.
- When the air is humid, i.e., contains water vapor droplets floating in it, it becomes a colloid.
- When the air is dirty, i.e., full of soot and dust particles, it becomes a suspension. (See What is the NH4 Lewis Structure?)
8. Is Air a Homogeneous or Heterogeneous Mixture?
Air is a homogeneous mixture when it is pure and dry. The composition of the air is mostly equal in all parts of the atmosphere. It becomes heterogeneous when it contains unequal amounts of water vapor in different places or when it is being polluted by chemical emissions or during dust storms. The composition of dust particles or water vapor is not uniform. So, air can be homogeneous and heterogeneous mixtures depending on the situation. (Also read When and How do Body Systems Work together?)
9. Is Air a Gas Liquid Mixture?
Air can be called a mixture of gases and liquids when humid. During rain or snowfall, air consists of water droplets and tiny ice crystals floating around. When the temperature is above the freezing point of water, the floating ice crystals become water droplets. So, during precipitation, air can become a gas-liquid mixture. (See How is Dew Formed?)
10. Why is Pure Air a Mixture?
Pure air is a mixture of elemental gases like nitrogen, oxygen and compound gases like carbon dioxide and methane. Without water vapor, the air is dry and pure. When not humid, dry air is a homogeneous mixture of various gases. A characteristic of a pure mixture is that its components can be separated into their original form. (See Why the Sky Colour is Blue?)
Similarly, pure air can be liquefied, and its components can be separated by performing a simple fractional distillation. If the air was a compound, the constituents couldn’t have been separated from it. Therefore, finally to answer, is air an element, it is not, we can say that pure air is only a mixture. (See What happens When Water Boils?)