Difference Between Pure Substance And Mixture

What Is A Pure Substance?

A pure substance also referred to as a chemical substance is a material that has a constant composition (is homogenous) and has consistent properties throughout the sample. Pure substances have the potential to form predictable products from chemical reactions. In chemistry, a pure substance consists of only one type of atom, molecule or compound.

The measure of whether a substance is pure or not is known as purity, a pure element or compound contains only one substance with no other substances mixed in.  For example pure iron would only contain iron atoms whereas pure sugar would contain molecules of sucrose. Impure materials may be mixtures of elements, mixtures of compounds or mixtures of elements and compounds.

Pure substances exhibit very well-defined physical properties or properties that are not connected with the substance’s ability to combine with different substances.

Examples of pure substances include chemical elements and compounds. Alloys and other solutions may also be considered pure if they have a constant composition. Examples include:

• Hydrogen gas
• Oxygen gas
• Gold
• Table salt
• Pure water
• Baking soda
• Ethanol
• Saline Solution
• Brass
• Bronze
• Diamond

What You Need To know About Pure Substance

• A pure substance is often described as substances that are made up of only one type of atom or molecule.
• Chemical and physical properties of pure substances remain the same throughout.
• A pure substance can be classified into solids, liquids or gases.
• A pure substance in its purest form does not contain impurities.
• In a pure substance, the constituents or components are present in fixed ratio or proportion.
• All pure substances have a uniform characteristic melting and boiling points.
• In a pure substance, each constituent does not retain its original properties.
• A pure substance cannot be separated into simpler substances by physical means.
• A pure substance usually participates in a chemical reaction to form predictable products.

What Is A Mixture?

A mixture is the physical combination of two or more substances in which the identities are retained and are mixed in the form of solutions, suspensions and colloids. Chemical bonds between the components are neither broken nor formed. Mixtures can be characterized by being separable by mechanical means e.g heat, filtration, gravitational sorting, centrifugation, decantation etc.

Note that even though the chemical properties of components remain unchanged, a mixture exhibits new physical properties like boiling point and melting point. For example, mixing together water and alcohol produces a mixture that has a higher boiling point and lower melting point than alcohol (lower boiling point and higher boiling point than water).

Two major categories of mixtures are heterogeneous and homogeneous mixtures. Heterogeneous mixtures are not uniform throughout the composition e.g gravel whereas homogenous mixtures have the same phase and composition, no matter e.g air.  

Other than being classified as heterogeneous or homogenous, mixtures may also be described according to the particle size of the components as follow:

• Solution: A chemical solution containing very small particle sizes (less than 1 nanometer in diameter).
• Colloidal: A colloidal solution appears homogenous to the naked eye but particles are apparent under microscope magnification.
• Suspension: Particles in a suspension are often large enough that the mixture appears heterogeneous.

Examples of mixtures

• Crude oil: A mixture of organic compounds (mainly hydrocarbons).
• Seawater:  A mixture of various salt and water.
• Air: A mixture of various gases like oxygen, carbon dioxide, nitrogen, argon, neon etc.
• Ink: A mixture of colored dyes.
• Gunpowder: A mixture of sulfur, potassium nitrate and carbon.
• Smoke: A mixture of solid particles and gases.

What You Need To Know About Mixture

• Mixture is usually described as a substance that is made up of the combination of two or more substances in different proportions.
• The chemical and the physical properties of mixtures vary due to presence of more than one compound.
• The mixtures are broadly classified into homogenous and heterogeneous mixtures.
• The mixture has impurities as it is made up of two or more substances.
• In a mixture, the constituents can be present in any ratio or proportion.
• All mixtures do not have same characteristic melting and boiling points.
• In a mixture each constituent retain its original properties.
• A mixture can be separated by physical means such as evaporation, magnetic separation etc.
• During the formation of a mixture, there is no change in energy.

Also Read: Difference Between Compound And Mixture

Difference Between Pure Substance And Mixture In Tabular Form

Also Read: Difference Between Elements And Compounds