CLASS 9TH 2020-21 SCIENCE {CHEMISTRY} CH 2 [IS MATTER AROUND US PURE ? BY :- TOPPER STUDY CIRCLE

TOPPER STUDY CIRCLE

CLASS 9^TH 2020-21

SCIENCE {CHEMISTRY}

CH 2 [IS MATTER AROUND US PURE ?

Main topics covered in this part of CBSE Class 9 Science,  Matter in Our Surroundings: Chapter Notes, are:

·         Matter and its Types

·         Elements

·         Compounds

·         Metals, Non-metals and Metalloids

·         Mixture and its Types

·         Solution and its Types

·         Solubility

·         Factors Affecting the Solubility

·         Concentration of Solution

Key notes for Chapter- Is Matter Around Us Pure, are:

Matter
Anything which has mass and occupies space is called matter. It may be solid, liquid or gas.
Types of Matter

It is of two types :
1. Pure Substance
2. Impure substance

1. Pure Substance: It  may be defined as a material which contains only one kind of atoms or molecules.
Pure substances are again of two types:

(a) Elements                    

                                                                                  (b) Compounds

(a) Elements:

·         Pure substances which are made up of only one kind of atoms are known as elements.

·         They cannot be split up into two or more simpler substances by any of the usual chemical methods.

·         For example: Iron, gold, silver, carbon, oxygen, nitrogen and sodium etc.

Elements are further grouped into the following three categories:

(i) Metals, for example: Iron, copper, gold, sodium, silver, mercury, etc.

(ii) Non – metals, for example: Carbon, oxygen, sulphur, nitrogen, oxygen, hydrogen, etc.

(iii) Metalloids : Boron, silicon, germanium, etc.

Properties of Metals:

·         These are lustrous (shine).

·         They conduct heat and electricity.

·         All metals are malleable and ductile.

·         They are sonorous.

·          All metals are hard except sodium and potassium.

·         All metals are solids at room temperature except mercury which is a liquid.

Properties of Non-metals:

·         These are dull in appearance.

·         They are poor conductors of heat and electricity except diamond which is a good conductor of heat and graphite which is a good conductor of electricity.

·         They are neither malleable nor ductile.

·         They are generally soft except diamond which is the hardest natural substance known.

·         They may be solids, liquids or gases at room temperature.

Metalloids: The elements that have properties intermediate between those of metals and non-metals, are called metalloids.

(b) Compounds:

·         It is a form of matter formed by combining two or more elements in a definite ratio by mass.

·         It Can be decomposed into its constituent elements by suitable chemical methods

·         For example: Water (H₂O), oxygen (O₂), Nitrogen dioxide (NO₂), etc.

2. Impure Substance:  It  may be defined as a material which contains only one kind of atoms or molecules.

It is also named as mixture.

Mixtures:
A mixture is a material which contains two or more different kinds of particles (atoms or molecules) which do not react chemically but are physically mixed together in any proportion.

Types of mixture

It is of two types:
(a) Homogeneous mixture       (b) Heterogeneous mixture

S. No.	Homogeneous mixture	Heterogeneous mixture
1.	All the components of the mixture are uniformly mixed.	All the components of the mixture are not thoroughly mixed.
2.	No separation boundaries are visible.	Separation boundaries are visible.
3.	It consists of a single phase.	It consists of two or more phases.
4.	Example: Sugar dissolved in water	Example: Air, sand and common salt.

Difference between mixtures and compounds:

S. No.	Mixtures	Compounds
1.	Various elements just mix together to form a mixture and no new compound is formed.	Elements react to form new compounds.
2.	A mixture has a variable composition.	The compound has a fixed composition.
3.	A mixture shows the properties of its constituents.	Properties of a compound are  totally different from those of its constituents.
4.	They do not have a fixed melting point, boiling point, etc.	They have a fixed melting point, boiling point, etc.
5.	The constituents can be seperated easily by physical methods	The constituents can be separated only by chemical processes.

Components of Solution:

(1) Solvent: The component of the solution that dissolves the other component in it and is usually present in larger amount, such component of solution is called the solvent.
For example: Water, alcohol etc.

(2) Solute: The component of the solution that is dissolved in the solvent and is usually present in lesser quantity, such component is called the solute.For example: Salt, sugar, iodine etc.

Properties of solutions:

(i) It is a homogeneous mixture.

(ii) Particle size in a solution is less than 1 nm in diameter.                      (iii) Particles of a solution cannot be seen even with a microscope.
(iv) A true solution does not scatter the light.
(v) Solution is stable.
(vi) The solute particles cannot be separated from the mixture by the process of filtration.

Types of solutions:

Various types of solutions are:

(i) Solid in a solid solution: Alloys.

(ii) Solid in a liquid solution: Sugar solution, salt solution.
(iii) Liquid sin a liquid solution: Lemon water, vinegar (acetic acid in water)
(iv) Gas in a gas solution: Air.

(v) Gas in a liquid solution: Soda water.

Solubility:

The maximum             amount of         the           solute      which           can be                        dissolved in                100 grams         of a solvent at a         particular           temperature is   known              as its                                solubility            in that              particular          solvent.

Conditions affecting solubility:                                                                       
(i) Temperature: Solubility of solids in liquids increases with the increase in temperature, whereas solubility of gases in liquids decreases on increasing the temperature.

(ii) Pressure: Solubility of gases in liquids increases on increasing thepressure, whereas the solubility of solids in liquids remains unaffected by the change in pressure.

Concentration of a Solution

It is defined as the mass of the solute in grams present in 100 grams of the solution.

Mathematical expression for concentration of solution:

In case of liquid solute in liquid solvent concentration can be expressed as:

Saturated Solution

A solution in which no more quantity of solute can be dissolved at a particular temperature, is called saturated solution.

Unsaturated Solution

A solution in which more quantity of solute can be dissolved without raising its temperature, is called unsaturated solution.

Suspension:

The heterogeneous mixture in which solids are dispersed in a liquid are called suspensions.  For example: Chalk-water mixture, muddy water, flour in water, etc.
A suspension is a heterogeneous mixture in which the solute particles do not dissolve but remain suspended throughout the bulk of the medium.

Properties of a Suspension:
(i) It is a heterogeneous mixture.
(ii) The particles of a suspension can be seen by naked eyes.

(iii) The particles of a suspension scatter a beam of light passing through it and make its path visible.
(iv) A suspension is unstable.
(v) Constituents of a suspension can be separated by the process of filtration.
Colloid or Colloidal solution:
Solutions in which the size of particles lies in between those of true solutions and suspensions are called colloidal solutions or simply colloids. For example: Milk, smoke and starch solution etc.

Properties of Colloids:
(i) A colloid is a heterogeneous mixture.
(ii) The size of particles of a colloid is too small to be individually seen by naked eyes.
(iii) The particles of a colloidal solution are big enough to scatter a beam of light passing through it.

(iv) A  colloid is quite stable.
(v) Colloidal particles cannot be separated by the process of filtration.

Tyndall Effect: The scattering of light by the colloidal particles is known as Tyndall effect.

It can be observed when:

·         A fine beam of light enters a room  through a small hole.

·         Sunlight passes through the canopy of a dense forest.

Note: The colloidal particles are not the true solutions as their particles are big enough to show the Tyndall effect, whereas the particles of a true solution do no show Tyndall effect.

The components of a colloidal solution:
(i) Dispersed Phase: The solute-like component or the dispersed particles in a colloid form the dispersed phase.

(ii) Dispersion Medium: The component in which the dispersed phase is suspended is known as the dispersing medium.

Types of Colloids:

Different types of colloids are discussed in the table given below:

Physical Change:
Those changes in which only physical properties of the substances change but no new substances are formed are called physical changes.
For example - Melting of ice to form water, breaking of glass, preparing a solution etc.
Chemical change:
Those changes in which new substances are formed are called chemical changes and chemical properties of a substance gets changed in a chemical change.

For example - Rusting of iron, bumning a piece of paper etc.

Difference between Physical and Chemical changes:

S. No.	Physical Change	chemical change
1.	Here only the physical properties like state, shape or size of a substance change.	It brings about a change in the chemical properties of a substance.
2.	There is no change in chemical composition of a substance.	There is always a change in chemical composition of a substance.
3.	No new substance is formed.	A new substance is always formed.
4.	It is temporary and hence reversible.	It is permanent and hence irreversible.

The separation of components of a Mixture:

Some of the important methods used to separate different mixtures are explained below::

(1) Evaporation:

Evaporation is a process which is used to separate a solid substance dissolved in liquid. It is based on the fact that liquids vaporize easily whereas solids do not.

Applications of Evaporation:

·         Obtaining salt from see water.

(2) Centrifugation:

It is a method of separating the suspended particles of a substance from a liquid in which the mixture is rotated at high speed in a centrifuge.

This method is useful in case the suspended particles in a liquid are too small too be retained by filter paper.

                                    

Principle of Centrifugation:
When a mixture is rotated very fast, the denser particles are forced to go to the bottom of the centrifuge and the lighter particles stay at the top.
Applications of Centrifugation:

·         Used in dairies to separate cream from milk.

·         Used in washing machines to squeeze out water from wet clothes.

 (3) Separating funnel

It is used to separate a mixture of two immiscible liquids, like oil and water.

Principle of Separating funnel :

When a mixture of two immiscible liquids is kept in a separating funnel,  the liquids separate out in layers depending on their densities with the heavier forming the top layer.
Applications of Separating funnel:

·         To separate mixture of oil and water.

·         In the extraction of iron from its ore where the lighter slag (molten waste material) is removed from the top by to leave the molten iron at the bottom of the blast furnace.

(4) Sublimation:

This method is used to separate those components from a mixture which can sublime on heating.

For example: Ammonium chloride, camphor, naphthalene etc, can be separated from their mixture by sublimation

                          

Applications of Sublimation:

·         Iron can be separated from a mixture of iron fillings and camphor (volatile).

·         Common salt can be separated from a mixture of salt and ammonium chloride (volatile).

(5) Chromatography

This method is used to separate two or more dissolved solids which are present in a solution in very small quantities.

Principle of Chromatography:

This method of separation is based on the fact that though two substances are dissolved in the same solvent but their solubilities can be different. The component which is more soluble in, rises faster and gets separated from the mixture.

Applications of Chromatography:

·         To separate colours in a dye by paper chromatography.

·         To separate drugs from blood.

(6) Distillation:

This method is used to separate a mixture solid in a liquid. It is the process of heating the liquid to form vapour, and then cooling the vapour to get back liquid.

It is used for the separation of components of a mixture containing two miscible liquids that boil without decomposition and have sufficient difference in their boiling points.

Principle of Distillation:

The volatile liquid evaporates on heating which can be recovered by cooling its vapours by the process of condensation.

Applications of Distillation:

·         It is used to remove salt from sea water to obtain drinking water.

(7) Fractional distillation

It is the process of separating two or more miscible liquids by distillation, the distillate being collected in fractions due to boiling at different temperatures.

Fractionating Column:

The apparatus used in this process is similar to that for simple distillation except a fractionating column which is fitted in between the distillation flask and the condenser. A simple fractionating colunrn is a tube packed with glass beads. The beads provide surface for the vapours to cool and condense repeatedly.

Principle of Fractional Distillation:

In a mixture of two or more miscible liquids, the separation of various liquids depends on their boilibg points. The liquid having lower boiling point boils first and can be obtained first from the fractionating column than the liquid having higher boiling point.

Applications of Fractional Distillation:

·         It is used to separate a mixture of miscible liquids like alcohol-water mixture.

·         It is used to separate cruid oil ‘petroleum’ into useful fractions like kerosene, petrol,  diesel, etc.

·         It is used to separate different gases of the air by taking the liquid air.

(8) Crystallisation :

Crystallisation is a process used to separates a pure solid in the form of its crystals from a solution. The process involves cooling a hot, concentrated solution of a substance to obtain crystals.

Applications of Crystallisation:

·         Purification of common salt obtained from sea water.

·         To obtain crystals of alum (phitkari) from impure samples.

·         To obtain pure copper sulphate from an impure sample.