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Is air a pure substance or a mixture?

We all are familiar with air. While studying pure substances and mixtures there comes a question Is air a pure substance or a mixture? Well, this article is all about explaining why air is regarded as a mixture, not as a pure substance.

TLDR;
Air is a gaseous mixture that contains nitrogen, oxygen, methane, nitrous oxide, and other gases. Because these gases retain their properties in air, air is considered a mixture.

What is air?

Air, contains gases comprising the Earth’s atmosphere. It contains a group of gases of nearly constant concentrations and a group with concentrations that are variable in both space and time. Air contains important substances, such as oxygen and nitrogen, that most species need to survive.

What is a pure substance?

A pure substance is made up of one kind of particle with constant structure, these structures are further divided into elements and compounds. Pure substance contains only one type of matter. It has a definite set of properties such as boiling point, melting point, and density.

What is a mixture?

When two or more pure substances are combined it forms a mixture. Here they are not combined chemically. Mixtures can be separated into components of pure substance. Mixtures can be classified on the basis of particle size into three different types: solutions, suspensions, and colloids.

Types of mixtures: –

Solutions- It is a homogeneous mixture consisting of two or more components in which the particle size is smaller than 1 nm. For example sugar in water.

Suspensions- It is a heterogeneous mixture in which the solid particles are spread throughout the liquid without dissolving in it.

Colloids- It is a mixture where one of the substances is split into very minute particles dispersed throughout a second substance.

Is air a pure substance or a mixture?

Air is a mixture of nitrogen, oxygen, carbon dioxide, water vapours, and some other gases. It also contains dust particles, dry air contains 78.09% nitrogen, 20.95% oxygen, 0.93% argon, 0.04% carbon dioxide, and small amounts of other gases. Air also contains a variable amount of water vapour, on average around 1% at sea level, and 0.4% over the entire atmosphere. The composition of air is not constant and changes from place to place.

We have a similar article on Is Milk A Pure Substance or a Mixture? You can check it out for information about whether milk is a pure substance or a mixture.

Now a question arises whether a mixture of two or more phases can be a homogeneous mixture or not for example a mixture of air and liquid air. If the mixture of two or more phases has a homogeneous composition, it can also be considered a pure substance. Because oxygen and nitrogen have different percentage compositions in liquid and gaseous states in equilibrium, liquid air and air cannot be regarded as pure substances.

Frequently asked questions

is air a pure substance or a mixture?

Because fractional distillation of liquid air can separate air into its constituents such as oxygen, nitrogen, and so on. So, air is a mixture instead of a pure substance.

Is air a pure substance or homogeneous mixture?

Homogeneous mixtures are ones in which the components are evenly distributed across the entire mixture.
All gases in air have a homogenous composition. As a result, air is an example of a homogenous mixture.

Why is air called a homogeneous mixture?

These gases are uniformly distributed throughout the air and cannot be easily distinguished from one another. As a result, it is a homogeneous mixture of different gases.

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