Difference Between Pure Substance and Mixture

Main Difference – Pure Substance vs Mixture

We come across a lot of substances such as water, fuel, food, beverages, and medicine during our daily activities.  All these substances fall into two major categories. They are either pure substances or mixtures. The main difference between pure substance and mixture lies in their composition. A pure substance contains only one kind of compound. It can be the same molecule or atom. Mixtures are composed of several kinds of compounds. However, it’s important to look at them individually in order to understand the nature of these substances better.

This article explains, 

1. What is a Pure Substance?
       – Definition, Composition, Properties, Examples

2. What is a Mixture?
       – Definition, Composition, Properties, Examples

3. What is the difference between Pure Substance and Mixture?Difference Between Pure Substance and Mixture - Comparison Summary

What is a Pure Substance

As mentioned above, a pure substance is composed of only one kind of substance. This cannot be separated into any other matter physically. The colour, texture, fragrance or taste of all the particles in a pure substance are the same. Elements and molecules are considered to be pure substances. They consist of only one component; hence, their physical and chemical properties are constant. Pure substances are of one phase and do not separate into two or more phases at a given temperature or pressure. They can be gas, liquid or solid.

Examples of pure substances

Gas:

H2 gas – composed only of H2 molecules. During normal pressure and temperature conditions, it exists in the gaseous phase. However, under extreme conditions, it tends to turn into a liquid.

Liquid:

Distilled deionized pure water- When water does not have any ions dissolved or any other substance dispersed, it is a pure substance in liquid form. However, water is often found naturally as a homogeneous mixture, with various other substances dissolved in it. Water is a liquid under normal conditions, but phase transfer happens when temperature and pressure are varied.

Solid:

Pure metals such as Gold, Silver, and Platinum are good examples for pure solid substances. These are often found as solids and can be turned into a molten liquid under high temperatures.

Pure substances have fixed melting points and boiling points, and this is very helpful in chemical synthesis to identify unknown substances. In organic chemistry, a melting point determination is very important to ensure that a certain desired chemical compound is isolated. The melting point of the unknown pure compound can be compared with that of known compounds to identify an unknown compound.

Key Difference - Pure Substance vs Mixture

What is a Mixture

Mixtures consist of two or more substances which can be separated by physical or chemical means. The components of a mixture are not chemically bonded, but physical attractions may be present. This is the reason for their easy separation by processes like filtration, distillation, chromatography, extraction and centrifugation. Properties of components of a mixture are retained even after mixing up. Furthermore, when sugar is dissolved in water, we can still taste the sweet taste of sugar in the solution.

The component ratio is not fixed and may vary from mixture to mixture. Therefore properties like melting point and boiling point are not fixed either.

Mixtures are either homogeneous or heterogeneous depending on the uniformity of composition.

Homogeneous Mixtures

The composition is the same throughout the mixture. Particles are arranged in an orderly way. The components are of either atomic level or molecular level. Homogeneous mixtures are of one phase. There is no layer separation.

Heterogeneous Mixtures

Unlike homogeneous mixtures, there is no uniformity in the composition. Components can be of two phases (ex:- suspensions, soil). Furthermore, they can be distinguished by the naked eye. We can see grains of a rice and sand mixture separately and identify each component.

Read More:

Difference Between Homogeneous and Heterogeneous Mixtures

Difference Between Pure Substance and Mixture

Difference Between Pure Substance and Mixture

Composition

Pure substance: Pure substances are made of only one matter; thus the composition is the same throughout.

Mixture: Mixtures are made up of several substances that are not chemically bonded.

Properties

Pure substance: Chemical and physical properties are constant.

Mixture: Chemical and physical properties may vary. Individual properties of components are retained.

Classification

Pure substance: Pure substances can be categorised as gas, liquid and solid. 

Mixture: Mixtures are categorised as homogeneous and heterogeneous.

Examples

Pure substance: Examples include pure water, H2 gas, gold.

Mixture: Examples include sand and sugar, oil and water.

Finally, it can be stated that almost everything on the earth is either a mixture or a pure substance. A mixture can be defined as a collection of two or more pure substances.

References:

Job, G.; Ruffler, R. Homogeneous and Heterogeneous Mixtures. Physical Chemistry from a different angle. 2016. 335-355.DOI 10.1007/978-3-319-15666-8_13

Image Courtesy:

“Pure-water-resources-are-limited-HD-screenshot” By Vadim A. Volochaev, ResearcherID: N-3239-2014 (Chemistry Department, Southern Federal University, Rostov-on-Don, Russia) – Own work via

“217074” (Public Domain) via

About the Author: Pabasara

Pabasara posses a Bachelor's Degree in Chemistry and is reading for M.Phil. in Chemistry. She has working experience in both academic and industry environments.

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