Is Matter Around Us Pure

The technique of Chromatography is used for separation of those solutes that dissolve in the same solvent.

This technique got its name after Greek word Kroma which means colour.

Is the Dye in Black Ink a Single Colour?

The ink that we use has water as the solvent and dye is soluble in it. As the water rises on the filter paper it takes along with the dye particles. Usually, a dye is a mixture of two or more colours. The coloured component that is more soluble in water, rises faster and in this way the colours get separated.

Distillation

The method of distillation is used for separation of components of a mixture containing two miscible liquids that boils without decomposition and have sufficient difference in their boiling points.

In this method mixture is taken in a distillation flask. A condenser is fitted with the distillation flask. A container, usually a beaker is taken near the outlet of condenser to collect the liquid after condensation. A laboratory thermometer is attached with the distillation flask to measure the temperature of liquid.

When the mixture is heated kept in flask, component of mixture when reaches its boiling point, start evaporating, and get collected after condensation in a container attached to it, leaving other liquid in the flask.

Example: the components of mixture of acetone and water can be separated using the method of distillation.

The boiling point of acetone is 56^o C, and that of water is 100^oC. Thus at 56^oC, acetone starts boiling and turns into gaseous phase, which is condensed using condenser and collected in a container leaving water in the distillation flask.

Fractional Distillation

Components of mixture of two or more miscible liquids which have difference in their boiling point less than 25K are separated using fractional distillation.

The apparatus of fraction distillation is similar to that of apparatus for simple distillation except fraction distillation has a fractional column is fitted in between the distillation flask and the condenser.

A simple Fractional Column is a tube packed with glass beads. The beads provide surface for the vapours to cool and condense repeatedly.

Fractional distillation is used in the separation of different gases from air, different fractions from petroleum products, etc.

How can We Obtain Different Gases From Air?

Air is a homogeneous mixture and can be separated into its components by the method of fractional distillation.

Flow diagram showing the steps of the process of separation different gases from Air

Separation of Oxygen from air

To separate Oxygen from air, other gases present in air are separated out. The air is compressed by increasing the pressure and is then cooled by decreasing the temperature to get liquid air. The liquid air is allowed to warm-up slowly in a fractional distillation column, where gases get separated at different heights depending upon their boiling points.

Process:

First air is put under high pressure, where because of hot air moisture present in air is expelled out as vapoour.

Then it is this air is passes through freezing cold water which decreases the temperature.

At this stage cold compressed air is blown in it.

At this stage air is passed through the region of cold compressed air where in separator carbon dioxide is separated out as dry ice.

After that liquid air is expanded in a chamber having fractional distillation column.

Here temperature is slowly raised.

At this stage nitrogen gas and argon gas are expelled out leaving liquid oxygen.

This liquid oxygen is collected in a container for further use.

Crystallisation

By the process of crystallization a pure solid in the form of crystals from a solution is separated out.

The technique of crystallization is better than simple evaporation technique as-

Some solid decomposes or some, like sugar may get charred on heating to dryness.

Some impurities may remain dissolved in the solution even after filtration. On evaporation these contaminate the solid.

How can we Obtain Pure Copper Sulphate From An Impure Sample

A crystal of pure sopper sulphate can be obtained from an impure sample by the method of crystallization.

Process:

Impure sample is dissolved in minimum amount of water and it is filtered to get rid of impurities.

Water is evaporated from the copper sulphate solution to obtain a saturated solution.

The saturated solution of copper sulphate so obtained is left undisturbed to get cooled slowly at room temperature.

After some hours usually after 10 to 12 hours or a day, the crystal of copper sulphate is obtained.

This crystal is pure form of copper sulphate.

Applications of Crystallisation

Purification of salt that we get from sea water.

Separation of crystals of alum (phitkari) from impure samples.

Supply of drinking water in cities

In cities water from river is purified and supplied to house households for drinking through pipe lines.

Steps in purification of water to supply in house holds

Step: 1. Water is stored in reservoir.

Step: 2. Sedimentation: Water is carried to the sedimentation tank where solid impurities are allowed to settle down.

Step: 3. Loading: From sedimentation tank water is carried to the loading tank to sediment the suspended impurities.

Step: 4. Filtration: From loading tank water is carried to the filtration tank through pipes. Filtration tank comprises of fine sand, gravel and coarse gravel. This filter impurities from water.

Step: 5. Chlorination: From filtration tank water is sent to the chlorination. By the process of chlorination bacteria present in water are killed.

Step: 5. After filtration and killing of bacteria using chlorination, water is transported to the house holds through pipe lines.

Physical And Chemical Changes

Physical Change:

Physical change is the change only in physical properties of a substance. After physical change the chemical properties of the substance remain same.

Exampe: Melting of ice into liquid water. And change of water into vapour.

Ice, water and vapour all have same chemical compositions. The chemical formula of ice, water and vapour is H_2O.

By melting of ice into water change of water into vapour only physical state of H₂ is changed. Ice is a solid, water is a liquid and vapour is a gas.

Thus, in physical change now new substance is obtained. Only the physical properties of a substance change.

Physical change is reversible.

Chemical Change

In chemical change new substance is obtained and chemical properties of substance is changed.

Example: Burning of coal, candle, or burning of anything is chemical change. As new substances are formed after burning and chemical composition of substance is changed.

A chemical change is considered irreversible. As it cannot be reversed using simple processes.

A chemical change is known as chemical reaction also.

What are the Types of Pure Substances?

Substances are classified into three types: Element, compound and mixture.

Element:

An element is the basic form of matter and cannot be broken into simpler substances by chemical reactions.

Element is the purest form of matter.

Example: Hydrogen (H), Helium (He), lithium (Li), Carbon (C), Oxygen (O), etc.

Elements are normally divided into three types: Metals, non-metals and metalloids.

Common Properties of Metals

Metals have a lusture (shine) and called metallic lusture.

Metals have silvery-grey or golden yellow colour.

Metals conduct heat and electricity.

Metals are ductile this means metals can be drawn into wires.

Metals are malleable this means metals can be hammered into thin sheets.

Metals are sonorous this means they produce ringing sound when hit.

Metals are solid at room temperature except mercury which is liquid at room temperature.

Gold, silver, copper, iron, etc. are some examples of metals.

Common properties of Non-metals

Non-metals are of variety of colours.

Non-metals are poor conductors of heat and electricity.

Non-metals are not lustrous, sonorous or malleable.

Non-metals are brittle.

Example: Hydrogen, oxygen, iodine, carbon, etc. are examples of non metals.

Metalloids

Some elements have intermediate properties between those of metals and non-metals, they are called metalloids, for example boron, silicon, germanium, etc.

Compounds

Substances composed of two or more elements, chemically combined with one another in a fixed proportion, are called compounds.

Example: water (H₂O), sodium chloride (NaCl), calcium carbonate (CaCO₃), etc. are some examples of compounds.