Separation Technique

In chemistry, many substances around us are found as mixtures.

A mixture may contain solids, liquids or gases mixed together. To use or study a substance properly, its components often need to be separated.

Separation techniques are methods used to separate the components of a mixture on the basis of their physical properties.

These physical properties may include:

• Particle size
• Solubility
• Density
• Volatility
• Boiling point
• Magnetic nature
• Ability to sublime

Filtration

Filtration is the process in which solid particles present in a liquid or gaseous fluid are removed with the help of a filter medium.

The filter medium allows the liquid or gas to pass through but retains the solid particles.

Principle Of Filtration

Filtration works on the difference in particle size.

In this process:

• Insoluble solid particles are retained by the filter paper or filter medium.
• Liquid passes through the filter paper.
• The liquid collected after filtration is called the filtrate.
• The solid left on the filter paper is called the residue.

Examples Of Filtration

• Separating chalk from water.
• Separating sand from water.
• Separating tea leaves from tea.

Filtration is useful when the solid is insoluble in the liquid.

Sublimation

Sublimation is the conversion of a substance from solid state directly into gaseous state without becoming liquid.

This method is used when one component of a mixture can sublime and the other cannot.

Principle Of Sublimation

Some substances change directly from solid to vapour on heating.

When the vapour is cooled, it changes back into solid.

This property is used to separate sublimable substances from non-sublimable impurities.

Examples Of Sublimation

Sublimation can be used for substances such as:

• Ammonium chloride
• Camphor
• Iodine
• Naphthalene

Example:

If ammonium chloride is mixed with sand, ammonium chloride can be separated by sublimation because it changes into vapour on heating and later deposits as solid on cooling.

Centrifugation

Centrifugation is a process used to separate or concentrate materials suspended in a liquid medium.

Under the influence of gravitational force, substances separate according to their density.

Principle Of Centrifugation

Centrifugation works on the difference in density.

When a mixture is rotated rapidly:

• Heavier particles move outward or settle down.
• Lighter particles remain above.

This method is useful for separating suspended particles from a liquid.

Examples Of Centrifugation

• Separating cream from milk.
• Separating butter from curd.
• Separating suspended particles from a liquid.

Chromatography

Chromatography is a separation technique in which the mixture to be separated is applied on a stationary phase.

A pure solvent, such as water or gas, is allowed to move slowly over the stationary phase.

The components of the mixture move with the solvent at different rates according to their solubility in the solvent.

Principle Of Chromatography

Chromatography works on the difference in solubility of different components in the same solvent.

In this process:

• The stationary phase remains fixed.
• The mobile phase moves over the stationary phase.
• Different components move at different speeds.
• Components get separated according to their solubility and movement.

Examples Of Chromatography

• Separating dyes from ink.
• Separating solutes that dissolve in the same solvent.

Chromatography is especially useful when components are present in very small quantities.

Distillation

Distillation is a separation technique used to purify liquids on the basis of difference in boiling points.

It involves heating a liquid mixture to vaporize the more volatile component.

The vapour is then cooled and condensed to obtain the purified liquid.

Principle Of Distillation

Distillation works on the difference in boiling points.

In this method:

• The mixture is heated.
• The component with lower boiling point vaporizes first.
• The vapour is passed through a condenser.
• The vapour cools and changes into liquid.
• The purified liquid is collected separately.

Simple Distillation

Simple distillation is used to separate a mixture of miscible liquids when there is a sufficiently large difference in their boiling points.

It uses simple apparatus with two flasks and a condenser.

Example:

• Purifying seawater.
• Separating common salt and water.

Fractional Distillation

Fractional distillation is an advanced form of distillation.

It is used when the components of a mixture have close boiling points.

It uses a more complex apparatus with a fractionating column.

Example:

• Refining crude oil.

Simple Distillation And Fractional Distillation: Difference

Basis	Simple Distillation	Fractional Distillation
Use	Used when boiling point difference is large	Used when boiling point difference is small
Apparatus	Simple apparatus with two flasks and condenser	More complex apparatus with fractionating column
Example	Purification of seawater	Crude oil refining

Principle Of Distillation

Separation of components takes place better when the relative volatility of a liquid is higher.

A more volatile liquid vaporizes more easily and can be separated from the mixture.

Decantation

Decantation is the process of separation of a liquid from solid or from immiscible liquids by removing the liquid layer at the top from the layer below.

This method is useful when:

• A solid settles at the bottom of a liquid.
• Two liquids do not mix with each other.

Principle Of Decantation

Decantation works on the difference in density and settling behaviour.

In a mixture of solid and liquid:

• Heavier insoluble solid settles at the bottom.
• Clear liquid remains above.
• The liquid is carefully poured off.

In a mixture of immiscible liquids:

• The lighter liquid remains above.
• The heavier liquid remains below.
• The upper layer can be removed carefully.

Examples Of Decantation

• Separating water from settled mud.
• Separating oil and water.
• Removing clear water after heavier impurities settle at the bottom.

Sedimentation

Sedimentation is the process in which heavier insoluble particles settle down at the bottom of a liquid.

Example:

If muddy water is kept undisturbed overnight, the heavier impurities settle at the bottom.

Sedimentation is often followed by decantation.

Evaporation

Evaporation is used to separate a solid dissolved in water or any other solvent.

In this method, the solvent changes into vapour and leaves behind the dissolved solid.

Examples Of Evaporation

• Obtaining common salt from seawater.
• Separating dye from ink.
• Separating a dissolved solid from water.

Magnetic Separation

Magnetic separation is used when one component of a mixture is magnetic.

A magnet is used to attract the magnetic substance and separate it from the non-magnetic substance.

Examples Of Magnetic Separation

• Separating iron filings from copper filings.
• Separating iron particles from a mixture.

Separating Funnel

A separating funnel is used to separate two immiscible liquids.

It works on the difference in density.

Example:

• Separating oil and water.

The heavier liquid forms the lower layer and is removed first through the tap of the separating funnel.

Hand Picking

Hand picking is used to separate large visible impurities from a mixture.

Example:

• Removing tiny pieces of stones from pulses before cooking.

This method is useful when the impurities are large enough to be picked by hand.

Churning

Churning is used to separate butter from curd.

In this method, curd is stirred or rotated so that butter separates from the liquid portion.

Important Separation Methods And Examples

Method	Used For	Examples
Filtration	Insoluble solid in liquid	Chalk and water, sand and water, tea leaves from tea
Sublimation	Sublimable solid from non-sublimable impurities	Ammonium chloride, camphor, iodine
Centrifugation	Suspended particles from liquid	Cream from milk, butter from curd
Evaporation	Solid dissolved in solvent	Common salt from seawater, dye from ink
Chromatography	Solutes dissolved in same solvent	Dyes from ink
Distillation	Liquid purification by boiling point difference	Common salt and water, seawater
Fractional distillation	Liquids with close boiling points	Crude oil refining
Decantation	Settled solid-liquid or immiscible liquids	Muddy water, oil and water
Magnetic separation	Magnetic and non-magnetic solids	Iron and copper filings
Separating funnel	Immiscible liquids	Oil and water
Hand picking	Large visible impurities	Stones from pulses

Choosing The Correct Separation Technique

Different mixtures need different separation methods.

• A mixture of chalk and water is separated by filtration.
• A mixture of sand and water is separated by filtration.
• Cream from milk is separated by centrifugation.
• Dye from ink is separated by evaporation.
• Common salt dissolved in water can be separated by evaporation.
• Dyes from ink can be separated by chromatography.
• Common salt and water can also be separated by distillation.
• Oil and water can be separated by separating funnel or decantation.
• Iron and copper filings can be separated by magnetic separation.

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FAQs On Separation Technique