Is Matter Around Us Pure? – Classification of Matter

In daily life, most of the substances around us are not pure. They are usually mixtures of two or more substances.

Chemically, matter can be classified into:

• Pure substances
• Mixtures

A pure substance contains only one kind of particles, while a mixture contains two or more kinds of particles.

Substance

A substance is one or more components that make up matter.

In chemistry, substances are studied according to their composition and properties.

Pure Substance

A pure substance is made up of only a single kind of particles.

Pure substances include:

• Elements
• Compounds

Pure substances have fixed composition and definite properties.

Mixture

A mixture is made up of two or more kinds of particles.

In a mixture, the components are not chemically combined.

They are mixed in any proportion and do not lose their individual identity.

Examples:

• Air
• Soil
• Sugar and water
• Oil and water

Element

An element is a substance which can neither be broken down into simpler substances nor formed from two or more simpler substances by any known physical or chemical process.

Important Facts About Elements

• Robert Boyle was the first scientist to use the term element in 1661.
• Antoine Lavoisier was the first to establish an experimentally useful definition of element.
• Hydrogen is an element because it cannot be split into simpler substances.
• Elements are regarded as the building blocks of the universe.
• Nitrogen is the most abundant element in the atmosphere.
• Oxygen is the most abundant element in the Earth’s crust.
• Oxygen and silicon are the main constituents of sand, soil and rocks.
• Elements may exist as solids, liquids or gases.

Examples Of Elements

State	Examples
Solid	C, S, Na, K, Ca, Ba, Fe, Ni, Co, Cu
Liquid	Hg, Br
Gaseous	H, N, O, F, Cl and noble gases like He, Ne, Ar, Kr, Xe, Rn

Classification Of Elements

Elements are broadly classified into:

• Metals
• Non-metals
• Metalloids

Compound

A compound is a pure substance made up of two or more elements chemically combined with one another in a fixed proportion by mass.

Example:
Water, or H₂O, is a compound made up of hydrogen and oxygen.

In pure water, hydrogen and oxygen are present in the ratio 1:8 by mass.

Other examples:

• Urea – NH₂CONH₂
• Ammonia – NH₃
• Sugar – C₁₂H₂₂O₁₁
• Washing soda – Na₂CO₃
• Chalk or limestone – CaCO₃

Properties Of Compounds

If energy is absorbed, the reaction is called endothermic.

The properties of a compound are entirely different from the properties of its constituent elements.

The elements of a compound cannot be separated by physical or mechanical methods.

A compound is a homogeneous substance.

A compound has a fixed melting point and boiling point.

Formation of a compound takes place through a chemical reaction.

Formation of a compound is accompanied by energy changes.

If energy is released, the reaction is called exothermic.

Mixtures

A mixture consists of two or more components, which may be elements or compounds.

The components are not chemically combined and are mixed in any proportion.

The components retain their individual identity.

Types Of Mixtures

Mixtures are of two types:

• Homogeneous mixture
• Heterogeneous mixture

Homogeneous Mixture

A homogeneous mixture has the same composition throughout.

It has no visible boundary between its components.

Homogeneous mixtures are also called solutions.

Examples:

• Air
• Sugar solution
• Salt solution
• Mixture of two miscible liquids

Heterogeneous Mixture

A heterogeneous mixture has a non-uniform composition.

Its components may remain visibly separate.

Examples:

• Soil
• Oil and water
• Sand and sugar

Properties Of Mixtures

• A mixture may be homogeneous or heterogeneous.
• Its composition is not fixed.
• It does not have a fixed melting point or boiling point.
• The properties of a mixture are the properties of its components.
• Formation of a mixture is not accompanied by heat or energy change.
• Components of a mixture can be separated by physical methods.

Examples of separation methods:

• Magnetic separation
• Filtration
• Evaporation
• Sublimation
• Distillation

Homogeneous And Heterogeneous Mixtures: Difference

Basis	Homogeneous Mixture	Heterogeneous Mixture
Composition	Uniform throughout	Not uniform throughout
Visible boundary	No visible boundary between components	Visible boundary may be present
Other name	Solution	No single common name
Example	Sugar and water	Oil and water
Liquids	Miscible liquids form homogeneous mixture	Immiscible liquids form heterogeneous mixture

Solution

A solution is a homogeneous mixture of two or more substances.

The substances present in a solution are called components of the solution.

The two main components are:

• Solute
• Solvent

Solute

The solute is the component present in lesser amount.

Example:
In sugar solution, sugar is the solute.

Solvent

The solvent is the component present in larger amount.

Example:
In sugar solution, water is the solvent.

Types Of Solutions

Solutions may be formed in different states.

Liquid Solution

Solid In Liquid Solution

Example:

• Sugar in water

Here, sugar is the solute and water is the solvent.

Another example:

• Tincture of iodine – iodine dissolved in ethyl alcohol

Gas In Liquid Solution

Example:

• Aerated drinks like soda water

In soda water, carbon dioxide gas is the solute and water is the solvent.

Liquid In Liquid Solution

Example:

• Acetic acid dissolved in water

Gaseous Solution

A gas in gas solution is a homogeneous mixture.

Example:

• Air

Air is mainly a mixture of nitrogen, oxygen and other gases.

Solid Solution

A solid in solid solution is commonly seen in alloys.

Example:

• Brass

Brass contains approximately:

• 70% copper
• 30% zinc

Zinc + Copper = Brass

Properties Of Solutions

• A solution is a homogeneous mixture.
• Particle size in a solution is less than 10⁻⁹ m, or 1 nm.
• Particles of a solution cannot be seen with the naked eye.
• Particles of a solution cannot be seen even with a microscope.
• Particles of a solution can pass through filter paper.
• Components of a solution cannot be separated by filtration.
• A solution is stable.
• Particles do not settle down when the solution is left undisturbed.
• A solution does not scatter a beam of light.
• Therefore, the path of light is not visible in a true solution.
• A true solution does not show Tyndall effect.

Concentration Of A Solution

The concentration of a solution tells the amount of solute present in a given amount of solution.

Mass Percentage

Mass percentage of solute is calculated as:

Mass % of solute = Mass of solute / Mass of solution × 100

Here:

• Solution = Solute + Solvent

Volume Percentage

Volume percentage of solute is calculated as:

Volume % of solute = Volume of solute / Volume of solution × 100

Aqueous And Non-Aqueous Solutions

Solutions may also be classified on the basis of solvent.

Aqueous Solution

A solution in which water acts as solvent is called an aqueous solution.

Non-Aqueous Solution

A solution in which solvent is other than water is called a non-aqueous solution.

Saturated, Unsaturated And Supersaturated Solutions

Saturated Solution

A solution that contains the maximum possible amount of solute at a given temperature is called a saturated solution.

Unsaturated Solution

A solution in which more solute can still dissolve at a given temperature is called an unsaturated solution.

Supersaturated Solution

A solution that contains more solute than a saturated solution under certain conditions is called a supersaturated solution.

Solubility

Solubility is the amount of solute that can be dissolved in 100 g of solvent at a given temperature.

The solubility of solids in liquids generally increases with rise in temperature.

Suspension

A suspension is a heterogeneous mixture in which solute particles remain suspended throughout the bulk of the solvent.

Example:

• BaSO₄ dispersed in water

Properties Of Suspension

• Suspension is a heterogeneous mixture.
• Particle size is greater than 100 nm, or 10⁻⁷ m.
• Particles of a suspension can be seen.
• They may or may not be visible with the naked eye, but can be seen with a microscope.
• Particles scatter a beam of light and make its path visible.
• Suspension is unstable.
• Particles settle down when left undisturbed.
• Suspension can be separated by filtration.

Colloidal Solution

A colloidal solution is a mixture in which the size of solute particles is intermediate between true solutions and suspensions.

The size of colloidal particles is between:

• 10⁻⁹ m and 10⁻⁷ m

or

• 1 nm to 100 nm

A colloidal solution is a heterogeneous mixture.

It consists of two phases:

• Dispersed phase
• Dispersion medium

Dispersed Phase

The dispersed phase is the component present in smaller proportion.

It is similar to solute in a solution.

Dispersion Medium

The dispersion medium is the component present in larger proportion.

It acts as the medium in which colloidal particles are dispersed.

It is similar to solvent in a solution.

Types Of Colloids

Dispersed Phase	Dispersion Medium	Type Of Colloid	Example
Solid	Solid	Solid sol	Some coloured glasses and gemstones
Solid	Liquid	Sol	Paints, cell fluids
Solid	Gas	Aerosol	Smoke, dust
Liquid	Solid	Gel	Cheese, butter, jellies
Liquid	Liquid	Emulsion	Milk, hair cream
Liquid	Gas	Aerosol	Fog, mist, cloud, insecticide sprays
Gas	Solid	Solid sol	Pumice stone, foam rubber
Gas	Liquid	Foam	Froth, whipped cream, soap-lather

Particle Size In True Solution, Colloid And Suspension

Type	Particle Size
True solution	Less than 1 nm
Colloidal solution	1 nm to 100 nm
Suspension	Greater than 100 nm

Brownian Motion

The zig-zag motion of colloidal particles is called Brownian motion.

Brownian motion is caused by the collision of colloidal particles with the molecules of the dispersion medium.

Properties Of Colloids

• A colloidal solution is a heterogeneous mixture.
• Its particles lie between 10⁻⁹ m and 10⁻⁷ m.
• Colloidal particles are too small to be seen with the naked eye.
• Colloidal particles scatter a beam of light.
• Because of scattering, the path of light becomes visible.
• This scattering of light is called Tyndall effect.
• A colloidal solution is quite stable.
• Colloidal particles do not settle down easily.
• Particles of a colloidal solution cannot be separated by normal filtration.

True Solution, Colloid And Suspension: Comparison

Basis	True Solution	Colloid	Suspension
Nature	Homogeneous	Heterogeneous	Heterogeneous
Particle size	Less than 1 nm	1 nm to 100 nm	More than 100 nm
Visibility of particles	Not visible	Not visible to naked eye	Visible or visible under microscope
Tyndall effect	Absent	Present	Present
Stability	Stable	Quite stable	Unstable
Filtration	Cannot be separated	Cannot be separated by normal filtration	Can be separated

Physical And Chemical Changes

Changes in matter may be physical or chemical.

Physical Change

A physical change is a change in physical properties such as size, shape or colour.

In a physical change:

• No new substance is formed.
• It is usually temporary.
• It can be reversed by changing conditions.
• The composition and chemical nature remain the same.

Examples Of Physical Change

• Glowing of electric bulb
• Boiling of water
• Dissolution of sugar
• Conversion of water into steam
• Melting of iron
• Bending of an iron rod
• Drawing a wire of iron metal

Chemical Change

A chemical change is a change in which new substances are formed.

In a chemical change:

• New substance is formed.
• It is permanent.
• It is irreversible in nature.
• Chemical composition changes.

Examples Of Chemical Change

• Electrolysis of water
• Burning of candle
• Rusting of iron
• Formation of iron sulphide from iron and sulphur
• Burning of magnesium ribbon
• Decaying of wood
• Burning of wood

Important Conceptual Points

• Only elements and compounds are pure substances.
• Mixtures are not pure substances.
• A compound can be separated into its components by chemical means.
• A mixture can be separated by physical means.
• An element cannot be further separated into simpler substances.
• A compound has fixed composition.
• A mixture may have variable composition.
• Colloidal solutions are heterogeneous in nature.
• True solutions do not show Tyndall effect.
• Colloids show Tyndall effect because their particles scatter light.
• If dispersed phase is liquid and dispersion medium is solid, the colloid is called gel.
• Whipped cream is an example of foam.
• Tincture of iodine contains iodine as solute and alcohol as solvent.
• Rusting of iron is a chemical change because hydrated iron oxide, or rust, is formed.

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