Pure Substances

What is Pure Substance?

Pure substances are formed by only one kind of particles and have either a fixed or constant structure. 


Pure substances are divided into elements and compounds further.


Elements are substances that cannot be broken down into simpler ones. An element cannot be transformed into a new element even by using any physical or chemical means. Elements mostly are metals, nonmetals, or metalloids.


On the other hand, compounds are also pure substances formed when two or more distinct elements are combined chemically with a fixed ratio of its atoms.


However, compound substances can be broken down into further separate elements using chemical methods.


Examples of Pure Substances

Few examples of pure substances include steel, iron, gold, diamond, water, copper, and many more. Air is also often considered as a pure substance.


What is a Mixture?

The mixture is a material composed of two or more different substances which are combined physically. A mixture can be usually separated back to its original components. Impure substances are also referred to as mixtures.


Mixtures are unlike chemical compounds because:

  • The substances of a mixture can be separated using some physical methods like filtration, distillation.

  • Mixtures always have variable compositions, whereas compounds have a fixed and definite composition.

  • When mixture forms, there is only a little or no energy change.


Some examples of mixtures include:

  • Crude oil - Mixture of some organic compounds, mainly hydrocarbons

  • Air - Mixture of different gases like nitrogen, oxygen, carbon dioxide, neon, and so on

  • Gunpowder - Mixture of potassium nitrate, sulfur, and carbon

  • Ink - Mixture of colored dyes which can be separated using chromatography

  • Blood - Mixture of numerous abundant substances including red and white blood cells; plasma, containing glucose, water, albumin, and so on

  • Mineral Oils - Mixture of branched, straight chained, and cyclic heavy alkanes

  • Soda - Mixture of sugar, water, and added flavors.


Characteristics of Mixtures

Fewer characteristics of Mixtures include:

  • The mixture is an impure substance

  • It has no formula

  • Mixtures can be fixed in any ratio

  • Mixtures can be of either homogeneous or heterogeneous

  • Their constituents can be separated easily using physical methods


Types of Mixtures

Mixtures are further classified into Homogeneous and Heterogeneous.


Homogeneous Mixtures are the ones that possess the same combination and properties throughout their mass. Every unit of the homogeneous mixture is likely to be every other unit.


One of the most common examples of homogeneous mixtures is sugar mixed with water. Because, if we liquefy sugar with water and blend it well, the resultant concoction is essentially the same no matter where we test it. Homogeneous mixture is composed of two or more chemical substances.


Heterogeneous Mixtures possess different compositions and properties in various parts. It means the properties won’t be uniform throughout the mixture.


For example, if we keep a little amount of sugar in a vessel, add some sand on the same, and shake the vessel twice, the concoction does not have the same configuration all throughout the jar. As the sand is heavy, there is a possibility that sand will be covered by the bottom part of the jar and whereas sugar will be occupied with the upper part. These mixtures can be visually identified and separated easily by physical means.


Some basic differences between homogeneous and heterogeneous mixtures are listed below.


Differences Between Homogeneous and Heterogeneous Mixtures


Homogeneous Mixture

Heterogeneous Mixture

These mixtures have uniform composition throughout the mixture.

These have a composition that may vary from point to point.

The whole mixture results in the same phase.

Substances can be of two phases and might with seperate layers.

Components cannot be easily separated.

Separation of components can be done easily.

‘Homo’ refers to the same.

‘Hetero’ refers to different.

Components cannot be seen with the naked eye.

Components can be seen easily.

Example - Air - Even though the air is composed of different gas molecules, they belong to the same phase and mixed uniformly.

Example - Oil and Water - Due to their different polarities, they do not mix.


Few of the points that differentiate mixtures and pure substances include:


Differences Between Pure Substances and Mixtures


Pure Substances

Mixtures

They have definite physical and chemical properties.

Mixtures don’t have a definite set of properties. They have them in different parts.

Have constant physical and chemical properties.

Have varying physical and chemical properties.

It is composed of various elements.

It is a combination of two or more substances or elements.

Components cannot be separated by any physical separation methods.

Can be separated by using separation methods like Magnetic separation,  Evaporation, and more.

Can be categorised as elements and compounds.

Can be categorized as only homogeneous and heterogeneous.

Examples include Pure water, Hydrogen gas, Gold.

Examples include a mixture of Sand and Sugar, Oil and Water etc. 

FAQ (Frequently Asked Questions)

Which are Good Examples of Homogeneous Mixtures?

Cement is one of the solid homogeneous mixtures of calcium compounds. If we mix it with sand, gravel, and water, it becomes concrete, thereby, and is one of the world's most popular construction materials.


Water itself is a liquid homogeneous mixture. All except the purest water contains dissolved minerals and gas. These are absorbed in the bath, and the liquid remains in the same phase and homogeneous.


Gas homogeneous mixtures, such as heliox and trimix, are used in SCUBA diving.

Which are Good Examples of Heterogeneous Mixtures?

A salad with cheese, lettuce, seeds, tomatoes, broccoli, and a few other vegetables is an example of a solid heterogeneous mixture.


Mud puddles are heterogeneous liquid mixtures. Dirt, leaves, and all manner of other precipitation mixes with rainwater and pools into a mixture where the elements can be easily identified.


Perfume and cologne are the well-known gaseous heterogeneous mixtures, with small droplets of fragrant substances drifting like a fog in which gas droplets are trapped in a liquid dispersion medium.

Why is Coffee a Mixture, but not a Pure Substance?

We already know that coffee is prepared with more than one substance. It contains water, caffeine, and many different chemicals from the coffee bean that produce the flavor or taste. Even though it is not a pure substance, it is a homogeneous type of mixture because it has the same composition throughout the mixture.