IS MATTER AROUND US PURE

For a common person pure means having no adulteration. But for scientist, all these things are actually a mixture of different substances and hence not pure.

For example- milk is actually a mixture of water, fat, proteins, etc.

MIXTURE

• Mixtures are constituted by more than one kind of pure form of matter, known as substance.

• A substance cannot be separated into other kinds of matter by any physical process.

• Example- dissolved sodium chloride (NaCl) can be separated from water by the physical process of evaporation but sodium chloride is itself a substance and cannot be separated by physical process into its chemical constituents.

TYPE OF MIXTURES

Depending upon the nature of the components that form a mixture, there are two types of mixtures.

1. Homogenous Mixture: A mixture that has a uniform composition throughout, known as a homogeneous mixture.

Example: salt solution in water, sulphur solution in carbon disulphide, tap water, petrol, honey, ink, etc

2. Heterogeneous Mixture: A mixture that contains physically distinct parts and has non-uniform compositions, known as a heterogeneous mixture.

Example: Mixture of iron fillings and sodium chloride, salt and sulphur, etc

SOLUTION

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

Example: lemonade, saltwater, etc.

Solution is not only in the form of liquid that contains solid, liquid or gas dissolved in it. But the solution can be solid (alloys) and gaseous solution (air).
Alloys: Alloys are a mixture of two or more metals or a metal and a non-metal and cannot be separated into their components by physical methods.
Example: Brass is a mixture of 30% zinc and 70% copper.
Solution has two components that are solute and solvent:

Solute: the component of the solution that is dissolved in the solvent is called the solute.
Solvent: the component of the solution that dissolves the other component in it, is called the solvent.

Example:

A solution of sugar in water is solid in a liquid solution. In this solution, sugar is the solute and water is the solvent.
A solution of iodine in alcohol known as 'tincture of iodine' has iodine (solid) as the solute and alcohol (liquid) as the solvent.
Aerated drinks like soda water are gas in a liquid solution. These contain CO2 (gas) as solute and water (liquid) as solvent.
Air is a mixture of gas in gas.

PROPERTIES OF SOLUTION

It is a homogeneous mixture.
The particles of the solution are smaller than 1 nm (10-9 m) in diameter. So, they cannot be seen with naked eyes.
They do not scatter a beam of light that is not visible in a solution.
The solute particle cannot be separated from the mixture by the process of filtration.
The solute particles do not settle down when left undisturbed, that is, a solution is stable.

CONCENTRATION OF A SOLUTION

In solution, the relative proportion of the solute and solvent can be varied. Depending upon the amount of solute present in a solution, it can be called a dilute, concentrated or saturated solution.

Saturated Solution: At any particular temperature, a solution that has dissolved a much solute as it is capable of dissolving is said to be a saturated solution.
Solubility: The amount of the solute present in the saturated solution at a particular temperature is called its solubility.
Unsaturated solution: If the amount of the solute contained in a solution is less than the saturation level, it is called an unsaturated solution.

The concentration of the solution is the amount of the solute present in a given amount (mass or volume) of the solution, or the amount of solute dissolved in a given mass or volume of solvent.

SUSPENSION

A suspension is heterogeneous mixture in which the solute particles do not dissolve but remain suspended throughout the bulk of the medium.

Properties of Suspension

It is a heterogeneous mixture.
The particle of a suspension can be seen by naked eyes.
Particles of suspension scatter a beam of light passing through it and make its path visible.
The solute particles settle down when suspension is left undisturbed, means a suspension is unstable.
The particles of a suspension can be separated by filtration.
When particle settle down the suspension brakes and it does not get a light.

COLLOIDAL SOLUTION

Colloidal solution is a heterogeneous mixture and which particle size is intermediate of true solution and suspension. Example: smoke from a fire.
The particles of a colloid are uniformly spread throughout the solution.
Due to the relative smaller size of particles, as compared to that of a suspension the mixture appears to be homogeneous but actually it is a heterogeneous mixture.

Tyndall effect

Particles of colloidal solution can easily scattered a beam of visible light. This is scattering of a beam of light is called the Tyndall effect.
Tyndall effect can be observed when a fine beam of light enters a room through a small hole. This happens due to a scattering of light by the particles of dust and smoke in the air.
Tyndall effect can also be observed when sunlight passes through the canopy of dense forest. In the forest, Mist contains tiny droplets of water which act as particles of colloid dispersed in air.

Fig. (a) solution of copper sulphate does not show Tyndall effect, (b) mixture of water and milk show Tyndall effect.

Properties of a colloid

A colloid is a heterogeneous mixture.
The size of particles of a colloid is too small to be individually seen by naked.
Colloids are big enough to scatter a beam of light passing through it and make its path visible.
They do not settle down when left undisturbed that is, it is quite stable.
They cannot be separated from the mixture by the process of filtration. But, a special technique of separation known as centrifugation can be used to separate the colloidal particles.

Dispersing medium

The components of colloidal solution are the dispersed phase and the dispersion medium. The solute like component are the dispersed particles in a colloid form the dispersed phase, and the component in which the dispersed phase is suspended is known as the dispersing medium.

Classification of colloids

Colours are classified according to the state (solid, liquid or gas) after dispersing medium and dispersed phase.

Example:

SEPERATING THE COMPONENTS OF A MIXTURE

Natural substances like minerals, clay, soil, milk, mineral water, sea water, ghee, juice, etc, are not chemically pure. Consequently, we use different methods for their separation into individual components. Various methods employed for separating mixtures into individual components are as follows:

1. Filtration

Filtration is a process in which the solute and the solvent are separated using filter paper. The difference in the solubility of the constituents is used to separate them in this process.

Basically, it is used to separate in soluble substances from liquid. The substance which is not soluble and remains behind on the filter paper is called Residue while the one which is filtered out is called filtrate.

Example: sand and water can be separated by the process of filtration.

2. Evaporation

Evaporation is a process that is used to separate a substance that has dissolved in water or any other liquid. The use of the process of evaporation for separating a mixture is based on the fact that liquids vaporize easily.

Evaporation is used for recovering dissolved solid substances from liquid mixtures or solutions but the liquid itself cannot be recovered by this method. The liquid vaporizes and gets lost in the air. Due to evaporation in which is a mixture of dye and water, we can obtain its constituent separately.

3. Crystallization

It is the process of cooling a hot, concentrated solution of a substance to obtain crystals is called crystallization. The process of crystallization is used for obtaining a pure solid substance from an impure sample.

This is done as follows:-

The impure solid substance is dissolved in the minimum amount of water to form a solution.
The solution is filtered to remove insoluble impurities.
The clear solution is heated gently on a water bath till a concentrated or a saturated solution is obtained then stops heating.
Allowed the hot concentrated solution to cool slowly.
Crystals of pure solid are formed. Impurities remain dissolved in the solution.
Separate the crystals of pure solid by filtration and dry.

4. Chromatography

Chromatography is a technique used for the separation of those solutions that dissolve in the same solvent in very small quantities is the most common paper chromatography. This separation is based on the fact that those two or more substances are soluble in the same solvent water but their solubility may be different.

It can be used to separate dies from ink.

The method for separation is as follows:-

Take a thin and long strip of chromatography paper. Draw a pencil line on it about 1 cm from one end.
Put a small drop of black ink on the chromatography paper strip at the centre of the pencil line. Let the ink dry.
When the drop of ink has dried for the chromatography paper strip is lowered into a tall glass containing some water in its lower part. The strip should be held vertically. The lower and should dip in water but pencil line should remain above the water level.
When the water reaches the top and, the strip is removed from the jar and dried. The paper containing separate coloured spots is obtained.

5. Sublimation

The changing of a solid directly into vapours on heating and of vapours into solid on cooling is called sublimation. The solid which undergoes sublimation is said to be sublime.

The process of sublimation is used to separate two substances from mixture with sublime on heating. The solid substance obtained by pulling the papers is known as sublimate. The substances like ammonium chloride camphor undergo sublimation.

The process of sublimation is used to separate that component of solid solid mixture with sublimes on heating.

Process of separation of common salt and ammonium chloride

Take a mixture of common salt and ammonium chloride in a China dish placed on a tripod stand.
Cover the China dish with and inverted glass funnel and put a cotton plug on the open end of the funnel to prevent vapours going to the atmosphere.
Heat the mixture using burner. On heating, ammonium chloride changes into white papers which rise up and get converted into solid Ammonium Chloride on coming in contact with cold inner walls of the funnel.
Here, pure ammonium collects on the inner wall of the Funnel in the form of supplement and can be removed. Since common salt is not prone to sublimation so it remains behind in the China dish.

6. Separation of two immiscible liquids

This process is used to separate two liquids which don't mix into one another.
These two immiscible liquids are separated through separating funnel.
A separating funnel is a type of funnel which has a stop cock in its stem to allow the flow of liquid from it, or to stop the flow of liquid from it.
The Separation of two immiscible liquids depends on the difference in their densities. Example: kerosene oil and water.
Kerosene oil having low density settle to the top of water and water is easily obtained by opening the stopcock of the funnel.

7. Separation of miscible liquids/distillation

This process is used to separate two liquids which are miscible that is the mixture into each other in all proportion and form a single layer when put in a container.
In this method, we start heating a liquid to Form paper then cooling the vapour to get back liquid.
The liquid obtained by condensing the vapour is called distillate.
This process is used for those liquids which have sufficient different in their boiling points.
This process is valid only when the difference is in boiling point is more than 25 k.

8. Fractional distillation

It is a process of separating two or more miscible liquids by distillation, the distillate being collected in fractions boiling at different temperature.
When the boiling point difference between two miscible liquids is less than 25k then fractional distillation is used. In this process former accept distillation Apparatus, a fractional in column is fitted in between distillation flask and the condenser.
A simple fractionating column has glass beads. These beads provide surface for vapour to cool and condensed supply.

9. Separation of gases from air

Air is a homogeneous mixture of gases and be separated into its constituents by fractional distillation.

Flow diagram shows the process of obtaining gases from air.

10. Centrifugation

Centrifugation is a method for separating the suspended particles of a substance from a liquid in which the mixture is rotated at high speed.
Centrifugation is done by a machine called centrifuge. The mixture rotate rapidly, a force acts on heavier suspended particles in it and bring them down to the bottom. The clear liquid being lighter remains on the top.
Example: cream from milk.

11. Cleaning water for drinking

To have clean water we need to pass the water obtains from lake through a long process.
It is as follows:

Sedimentation tank: Heavy impure particles settle down when water is left for some time.
Loading tank: Alum is mixed with water for stop even small suspended particles settle down.
Filtration tank: It has three layers of fine sand, coarse sand and tiny stones. When water passes through then it is further cleaned.
Chlorination tank: Chlorine is mixed with water in the time. It kills germs. Now water is sent to home.

PHYSICAL ANND CHEMICAL CHANGES

The inter-conversion of states is a physical change because these changes occur without a change in composition and so on change in the chemical nature of the substance.

Ice water and water vapour all look different and display different physical properties they are chemically the same whereas both water and cooking oil are liquid but their chemical characteristics are different. They are different in odour and inflammability.

Oil burns in air whereas water extinguishes fire. It is chemical property of oil that makes it different from water.

Burning is a chemical change for stop during this process one substance reacts with another to undergo a change in chemical composition.

Chemical change brings change in the chemical properties of matter and we get new substances. A chemical change is also called a chemical reaction.

TYPES OF PURE SUBSTANCES

On the basis of their chemical composition, substances can be classified either as elements or compounds.

1) Elements

Robert Boyle was the first scientist use the term element in 1661.
Antoine Laurent Lavoiser (1743-94), a French chemist, the first to establish an experimentally useful definition of an element. He defined an element as a basic form of matter that cannot be broken down into simpler substances by chemical reactions.
Elements can be divided into metal, non-metals and metalloids.

Properties of metals

They have lustre (shine).
They have silvery-grey or golden-yellow colour.
They conduct heat and electricity.
They are ductile (can be draw into wires).
They are malleable (can be hammered into thin sheets).
They are sonorous.
Example: gold, silver, copper, iron, sodium, potassium, mercury, etc.
Mercury is the only metal that is liquid at room temperature.

Properties of non-metals

They display variety of colours.
They are poor conductors of heat and electricity.
They are not lustrous, sonorous and malleable.
Example: hydrogen, oxygen, iodine, carbon (coal, coke), bromine, chlorine, etc.
Some elements have intermediate properties between those of metals and non-metals, they are called metalloids.

2) Compounds

A compound is a substance composed of two or more elements, chemically combined with one another in a fixed proportion.

Example: the ratio of oxygen to carbon in pure carbon dioxide is same whether, this gas is obtained by the oxidation of carbon or carbon monoxide.

Characteristics of Compounds

A compound is always homogeneous.
The proportion of different constituents of a compound is always fixed.
A compound differs in physical properties and chemical properties from the constituent elements of which the compound is formed.
A compound cannot be separated into its constituents or elements by physical or mechanical means.
The formation of a compound from its elements is occur by either libration or absorption of energy.
A compound possesses definite melting and boiling points.

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