9th science

Is Matter Around Us Pure

Separation of Components of Mixture

Centrifugation

In the method of centrifugation, the centripetal and centrifugal forces are used to separate lighter and heavier components of mixture of two immiscible liquids. This process is used to separate very small solids particles from a liquid mixture.

Example – Milk is the mixture of fat, water, and other constituents. Using the method of centrifugation, most of the fat can be separated from milk. In milk, fat is suspended throughout the milk which is separated out using the method of centrifugation.

When milk is churned rapidly, water which is heavier than fat, migrates away from the centre of centrifuge while fat is forced towards the bottom, which is drained out.

Application of centrifugation

  • In pathological test of blood and urine.
  • In separation of fat from milk.
  • In washing machines to squeeze the water from wet clothes.


Decantation

Decantation is used to separate the components from a mixture of two immiscible liquids, such as mixture of oil and water. In a mixture of two immiscible liquids, lighter one and heavier one form separate layer. The lighter one can be decanted after settling of mixture, carefully in other container.

In the process of decantation some of the heavier liquid also poured out with lighter one. Therefore, components from a mixture of two immiscible liquids; can be separated more easily and accurately using a separating funnel.

A separating funnel is usually made of glass with a stop cork with drain pipe at bottom. The heavier liquid which is settled at bottom is drained out from the mixture of two immiscible liquids by opening of stop cork from a separating funnel.

Sublimation

There are many substances which are converted into gas from solid when heated, and converted from gas to solid when cooled without converting into liquid. Such substances are known as sublime. For example – ammonium chloride, naphthalene balls, camphor, etc. Therefore, mixture of one sublime and other substance can be separated using the method of sublimation.

The mixture of ammonium chloride and common salt can be separated out using the process of sublimation. For this, the mixture is heated in a China dish. The China dish is covered by an inverted funnel. Cotton is used for plugging the opening of the funnel. After heating, ammonium chloride is converted into vapour and gets deposited over the inner surface of funnel; due to cooling. This leaves the common salt in China dish. Ammonium chloride can be taken out by scratching from the inner wall of funnel.


Chromatography

Chromatography is a method of separation which works on the principle of travel speed of components of a mixture. This method is used for separating dyes and pigments from a mixture. Ink is the mixture of dyes of different colours.

There are many types of chromatography. The dyes from an ink can be separated using paper chromatography.

For this, a strip of filter paper is dipped in the ink. Particles of dye start rising on filter paper; along with water. Different dyes rise with different speed because of different types of solubility in water and go up to certain heights.

Application of chromatography

  • In the separation of colours from a dyes.
  • In the separation of pigments from natural colours.
  • In the separation of drugs from blood for pathological tests.


Distillation

The process of distillation is used to separate two miscible liquids. The technique of distillation is based on the difference in boiling points of components of mixture of miscible liquids. Distillation is to separate the liquids which do not decompose even upto their boiling points and should boil at more than 250C.

In the process of distillation, the mixture is heated after keeping in a retort or distillation flask. The liquid which boils at lower temperature is vaporized at lower temperature. The vapour so obtained is passed through a tube and gets condensed in a separate container; leaving liquid with higher boiling point in the retort or distillation flask.

Distillation is used to separate the components of the mixture of two miscible liquids that boils without decomposition and have sufficient difference in their boiling points.

The process of distillation is used to purify many liquids, such as water.

Fractional Distillation

Fractional distillation is the process of separation of components of mixture into parts or fraction on the basis of fractional differences in their boiling points.

Fractional distillation is done when the difference in boiling points of the components of miscible liquids is less than 250C. In the process of fractional distillation, a fractional column is used along with retort or distillation flask.

Fractional column is a tube which contains glass beads, which facilitate surface for the vapour to cool and condense repeatedly.

Example – Ethanol and water are separated from their mixture using fractional distillation. The boiling point of water is 100⁰C while the boiling point of ethanol is 78.4⁰C. Since the difference of their boiling point is less than 25⁰C, thus they are separated using fractional distillation.

Some of the Applications of Fractional Distillation:

  • In petroleum refineries, petrochemical and chemical plants, natural gas processing and cryogenic air separation plants.
  • In oil refineries to separate crude oil into useful substances (or fractions).
  • In the process of organic juice.
  • In the separation of oxygen, liquid nitrogen and argon from air.


Separation of different gases from air

Air comprises of nitrogen, oxygen, carbon dioxide and argon as major components. Since air is the cheapest source of these gases, thus these are extracted from air at large scale

After liquefaction of air by repeated compression and cooling; nitrogen, oxygen, carbon dioxide and argon are extracted using fractional distillation.

Liquid nitrogen has boiling point equal to - 190⁰C and thus turns into gas first and separated from air.

The boiling point of argon is - 186⁰C, therefore it is extracted after argon.

The boiling point of oxygen is - 183⁰C, thus it is collected after the extraction of argon.

Carbon dioxide turns into solid at a temperature of - 97⁰C, therefore, it is removed while air is put under liquefaction.

Physical and Chemical Changes

Physical Change: The change in which no new substance is formed is called a physical change. During a physical change, chemical properties do not change but physical properties do change.

Chemical Change: The change in which a new substance is formed is called a chemical change. During a chemical change, chemical properties change.

Pure Substances

Elements and Compounds are considered as pure substances.

Elements: Substances that is made of only one element are called elements, such as hydrogen, carbon, oxygen, silver, gold, etc.

Compounds: Substances that is made of one or more elements by chemical combination are called compounds, such as water, carbon dioxide, copper oxide, hydrochloric acid, etc.

A compound does not contain the properties of its constituent elements and shows quite different characteristics.