Introduction: When we go to our shopping mall, we notice  the word pure  written on packs of many items on a packet of food items like milk packet,fruit juice etc.

              For common person pure means there is no adulteration in this things and therefore these are pure.

A pure substance consists of a single type of particles and cannot be separated into other kinds of matter by any physical process.

          A pure substance represent a single substance.

All the matter around us is of two types:-

1. Pure substance 2. Impure substances (mixture).

Pure substance: Pure substance represent a single substance.

Impure substance (mixture): Mixture is made up of two or more pure substances.

           Substances which make a mixture are called constituents or components.

Example:-lemonade is a mixture of water, lemon juice, salt and sugar.

        A mixture can be separated by physical methods into two or more pure substances.

Types of pure substances:-

1. Elements:- Robert Boyle was the first scientist to use the term element in 1661.

             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.

Example: hydrogen, nitrogen etc.

Made up of only one kind of atoms.

The elements are regarded as the building blocks of the universe.

Elements may be solids, liquids and gases.

Classification of elements:-

1. Metals 2. Non metals 3. Metalloid

1. Metals:- Metals have following properties

(i) Metals have a lustre (shine) and can be polished.

(ii)Good conductors of heat and electricity.

(iii)They are malleable ductile and have high melting point and boiling point.

Example gold aluminium

2. Non metals:-Non metals have following properties

(i)Non lustrous work conductor of heat and electricity.

(ii)Variety of colour soft and brittle low melting point and boiling point.

3. Metalloid:-Intermediate properties between those of metals and non metals example silicon(Si), germanium(Ge).

Compounds:- 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 H₂O combined ratio 1: 8

Properties:-

1.Compound consists of two or more elements combined together in a fixed proportion by mass.

2.Compounds are totally different from those of its component element.

3.Component element of compound cannot be separated by mechanical or physical methods.

4.Heterogeneous substance, fixed melting point and boiling point.

5.Compound occurs because chemical reaction and is accompanied by energy changes, they are called chemical compounds.

Mixtures:- Substance consists of two or more pure substances (element or compound) mixed together in any proportion and their components do not lose their properties example oil, air etc.

Types of mixture:-

1. Homogeneous:- It has the same composition throughout the sample. example salt solution.

2. Heterogeneous:- It consists of two or more parts are (called phases) and have different composition. example mixture of iron filling and sodium chloride

Properties

1. Main be homogeneous or heterogeneous.

2. Composition is not fixed and variable does not have define melting point and boiling point.

3. Properties as same as its component, not change in heat, easily separated its component by physical methods.

Solution:-A solution is a homogeneous mixture of two or more substances. example lemonade, soda water etc. At particle level there is homogeneity.

          General solution is made up of two constituents.

1. Solvent:- A component present in large amount in solution.

2. Solute :-Present in less amount in solution.

Different types of solution are in which solid or gas act as a solvent.

1. Solution of sugar and water is solid in liquid solution.

2. Tincture of iodine is solid in liquid solution.

3. Vinegar is liquid in liquid solution which is used as a preservative.

4. Aerated drinks like soda water or gas in liquid solution.

5. Air is gas in gas solution, this is is an example of gaseous solution.

6. Mixture of copper and gold is solid in solid solution.

Metal alloys:- These are homogenous mixture of two or more components.

     This can be separated by any physical method.

These are considered as mixture because this show the properties of its components example brass is a mixture of approximately 70% of Cu and 30% of Zn.

Solution can be divided into aqueous and non aqueous was on the basis of their solvent:-

1. Aqueous solution in which water is used as a solvent example common salt dissolve in water.

2. Non aqueous solution in which water is not used as a solvent example bromine dissolve in chloroform.

Properties of solution:-

1. It is a homogeneous in nature i.e homogeneity  at micro level.

2. Particle size less than 10^-9 m (1nm) cannot be seen even with the help of microscope.

3. Solution is a stable i.e particles does not settle down and they do not scatter beam of light.

N.B: Solution of substances have many advantages in industries medicines and laboratories.

Concentration of solution:- It may be defined as the amount of solute dissolved in a given amount (mass or volume) of solvent. 

Concentration= amount of solute/ amount of solvent.

      It may be also defined as-

Concentration =amount of solute/ amount of solution .

1. Mass percentage:-

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

Mass of solution =mass of solute+ mass of solvent.

2. Volume percentage:-

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

Saturated solution:- No more solvent can be dissolved at a given temperature is called saturated solution.

Unsaturated solution:- The amount of solute is less than the  saturation level is called unsaturated solution.

Supersaturated solution:- Amount of solid more than saturation level.

Solubility:-Amount of solute which can be dissolved in 100 g of solvent at a given temperature is called its solubility.

          Solubility of solids in liquids increases with increase in temperature.

Suspension:- It is a heterogeneous mixture in which the solid particles do not dissolve but remain suspended through out the bulk of the solvent.

Properties :-

1. It is a homogeneous mixture size of particle bigger than10^-7 or 100nm(10^-5).

2. Particle can be seen easily, it may or may not be by naked eye. But they are visible under microscope.

3. Scatter a beam of light and make its path visible, suspension is unstable i.e particle settle down.

4. It can be separated from mixture by the process of filtration.

Colloidal solution :-A solution in which the size of the solid particles is intermediate between those in true solution and suspensions.

         In other words, particles of colloidal solution are bigger than true solution and smaller than suspension.

     Colloidal solution is heterogeneous mixture.

It consists of two phases.

1. Dispersed phase 2. Dispersion medium.

Dispersed phase:- Component in which particle of colloidal dimension(10^-9m to 10^-7m in small proportion.

Dispersion medium :-Component which is present in excess proportion and act as a medium in which colloidal particles are dispersed. example sulphur in water, sulphur particle is considered dispersed phase and water act as a dispersion medium

Brownian movement of colloids:- Zig zag motion of colloidal particles is called Brownian movement.

Tyndall effect of colloids:- Scattering of light by colloidal particles as a result of which the path of the beam becomes visible is called tyndall effect.

Properties of colloids.

1. Heterogeneous mixture, consists of dispersed phase and dispersion medium.

2. Size of particle is in between 1 nm(10^-9m or 10^-7cm) i.e too small seen by naked eyes

3. They show tyndall effect, quite stable, particles do not settle down when left undisturbed.

4. Particles cannot be separated from mixture by filtration process. 

         They can be separated by a special technique called centrifugation.

Separating the components of a mixture:- Different methods are used to get individual components from the mixture.

        The colour component can be obtained from blue black ink by evaporation.

   The process of separating any substance from its solution by removing water is called evaporation.

     This method can be used to separate non volatile component (solute) from its volatile component (solvent).

Centrifugation:- Method of separating the solid particles suspended in liquid is called centrifugation.

        Cream from milk can be obtained by this process of centrifugation.

    It is used in diagnostic laboratories for investigate of blood and urine.

Separating funnel:- The immiscible liquid can be separated by a separating funnel.

        To separate the mixture of oil and water, mixture compound present in aqueous solution.

Sublimation:- Mixture of common salt and ammonium chloride can be separated by the process of sublimation.

      It is used for separating those substance which sublime on heating.

Distillation:- Be this process we separate two miscible liquids from a mixture.

     Separation of volatile liquids from non volatile impurities.

Fractional distillation:- If the boiling point of two miscible liquid is 25°C less then fractional distillation is apply.

    Air can be separated into their constituent gases by this process.

   Air can be compressed to form liquid air liquefied air.

The boiling point of liquid nitrogen (present in air) is  the lowest (-196°C). Nitrogen gets distilled first of all.

Liquid organ has slightly higher boiling point (-186°C). Therefore distilled after nitrogen.

Liquid oxygen has higher point (-183°C). Therefore distilled after argon.

Crystallisation:- Process in which we separate a pure solid in the form of crystals from a solution.

      The crystallisation technique is better than simple evaporation technique.

        The technique has been used for:-

1. Getting pure sugar from an impure sample.

2. Purification of Salt from seawater.

3. Separation of crystals of atom from impure sample.

Chromatography:- Special method to separate small amount of dissolved solids.

    Technique used for separation of those solutes that dissolve in in same solvent in different extent.

        It is also used to separate coloured substance.

It is used to identify sugar from urine sample and drugs from blood.

Physical change :-Physical property of the substances changes but no new substances are formed are called physical change. Conversion of water into steam, boiling of H₂O

Chemical change :-Changes in which new substances are formed are called chemical changes. example in electrolysis of water

Some important facts:-

1. The earth's crust is made mainly from two elements i.e Oxygen (46.6%) and silicon (27.7%). The rest of the elements are present in lesser proportions.

2. It is not possible to get carbon dioxide by simply mixing coke with Oxygen gas.

3. Elements and compounds are pure substances. Mixture are not pure substances in terms of science.

4. While heating sulphur in a dish, eye must be kept away from the vapour of sulphur. These are poisonous and cause irritation to the eyes.