CLASS- IX

SUBJECT – CHEMISTRY

LESSON 2 – IS MATTER AROUND US PURE

INTRODUCTION

MATTER- Anything which have mass and occupy space.

CLASSIFICATION OF MATTER- It is of two types:

i) Pure substances &

ii) Mixtures

Pure substances :- A pure substance consists of a single type of

particles. In other words, a substance is a pure single form of matter. For

example- iron, copper, oxygen, water etc.

On the basis of their chemical composition, substances can be classified either

as element or compounds.

Elements:- Element is a basic form of matter that cannot be broken down into

simpler substances by chemical reactions. For example:- gold, silver, sodium ,

carbon etc.

Compounds – A compound is a substance composed of two or more elements,

chemically combined with one another in a fixed proportion. For example:-

water, carbon dioxide, salt etc.

MIXTURES- Mixtures are constituted by more than one kind of pure

form of matter, known as a substance. A substance cannot be separated

into other kinds of matter by any physical process.

Types of mixtures :-

Homogeneous mixture- A mixture is said to be homogeneous if all the

components of the mixture are uniformly mixed and there are no

boundaries of separation between them. For example – sugar or salt in

water.

Heterogeneous mixture – A mixture is said to be heterogeneous if all the

components of the mixture are having non-uniform composition and there

are visible boundaries of separation between them. Example – water and

sand , sand and sugar etc.

ELEMENTS –

The number of elements known are more than 100.

92 elements are naturally occurring.

Two elements are liquid at room temperature – mercury and bromine.

Gallium and cesium become liquid at a temperature slightly above room

temperature.

Elements can be divided into:-

Metals

Non- metals and

Metalloids.

Metals :- Examples of metals are gold, silver, copper, iron, sodium etc.

Properties of metals:-

i) Electropositive in nature.

ii) They have lustre.

iii) They are hard.

iv) They have silvery grey or golden-yellow in colour.

v) They conduct heat and electricity.

vi) They are ductile.

vii) They are malleable.

viii) They are sonorous.

ix) Have high melting and boiling point.

x) High tensile strength.

Non- metal :- Examples of non-metals are hydrogen, oxygen,

iodine, carbon etc.

Properties of non- metals :-

i) They are electronegative.

ii) They display a variety of colours.

iii) They are lustrous

iv) They are poor conductors of heat and electricity.

v) They are not ductile.

vi) They are not malleable.

vii) They are not sonorous.

viii) Have low melting and boiling point.

Metalloids –Some elements have intermediate properties

between those of metals and non- metals, they are called

metalloids. They are semi-conductors. For example- boron,

silicon, germanium etc.

Solutions

A solution is a homogeneous mixture of two or more substances. For example: Lemon water, sugar solution, soda water, etc.

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, etc.

EXAMPLES:-

A solution of sugar in water is a solid in liquid solution.

Aerated drinks like soda water etc.

Properties:

It is a homogeneous mixture.

Its particles are too tiny and have a diameter less than 1 nm.

The particles are not visible to naked eyes.

Particles do not scatter a beam of light passing through it and hence do not show the Tyndall effect.

The solute particles never settle down on keeping undisturbed. Thus solution is quite stable.

The components of a solution cannot be separated using filtration.

Alloys

Alloys are homogeneous mixtures of two or more metals or a metal and a non metal and cannot be separated into their components by physical methods. Examples:

Bronze, a combination of copper (metal) and tin (metal).

Brass, a mixture of copper (metal) and zinc (metal).

Concentration of Solutions

TYPES OF SOLUTIONS-

SATURATED SOLUTION- When no more solute can be dissolved in a solution at a given temperature, it is called a saturated solution.

UNSATURATED SOLUTION- If the amount of solute contained in a solution is less than the saturation level, it is called an unsaturated solution.

Solubility

The amount of the solute present in the saturated solution at particular temperature is called its solubility.

Ways of representing the concentration of a solution

The concentration of a solution can be represented in many ways

(i) Mass by the mass percentage of a solution = (Mass of solute / Mass of solution) × 100

(ii) Mass by volume percentage of a solution = (Mass of solute/ volume of solution)×100

Suspensions

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

PROPERTIES-

It is a heterogeneous mixture.

Particles of suspension can be seen by the naked eye.

Particles of suspension scatter a beam of light passing through it.

The solute particles settle down when a suspension is left undisturbed, that is, a suspension is unstable.

They can be separated from the mixture by filtration process.

Colloids

A colloidal solution appears to be homogeneous but actually it is heterogeneous mixture in which the size of particles lies between solution and suspension. For example; milk etc.

Tyndall Effect

Colloidal particles scatter a beam of visible light. This phenomena is called Tyndall effect .

e.g.It can be observed when sunlight passes through the canopy of a dense forest.

PROPERTIES-

It is a heterogeneous mixture.

The size of particles of a colloid is too small to be individually seen by naked eyes.

Scatter a beam of light.

They do not settle down when left undisturbed.

They cannot be separated by the process of filtration.

Dispersed phase

The solute-like component of the dispersed particles in a colloid form the dispersed phase.

Dispersion medium

The component in which the dispersed phase is suspended is known as the dispersing medium.

COMMON EXAMPLES OF COLLOIDS

SEPARATING THE COMPONENTS OF A MIXTURE:-

Heterogeneous mixtures can be separated into their constituents by simple physical methods. Methods include: handpicking, sieving, filtration. Sometimes special techniques have to be used for the separation of the components of a mixture.

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.

(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: The denser particles are forced to go to the bottom of the centrifuge and the lighter particles stay at the top when spun rapidly. Applications of Centrifugation:

Used in dairies to separate butter from cream. Used in diagnostic laboratories for blood and urine tests. 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. 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

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. 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: 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.

(7) Fractional distillation To separate a mixture of two or more miscible liquids for which the difference in boiling points is less than 25 K, fractional distillation process is used.

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

Applications of Fractional Distillation:

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

It is used to separate different gases from the air.

Separating different Gases from the Air

Method – Fractional Distillation

Compress and cool the air by increasing the temperature and decreasing the

pressure. The air turns to liquid air.

Liquid air is warmed up slowly in a fractional distillation apparatus

The several components of air get separated and are collected at various

heights on the basis of their boiling point.

8) Crystallisation : Crystallisation is a process used to separates a pure solid in the form of its crystals from a solution.

CLEANING WATER FOR DRINKING:-

In cities drinking water is supplied from water works. Processes involved:-

Reservoir- The source of water supply in a city is either a nearby river or a lake (called reservoir).

Sedimentation tank- Heavy impure particles (insoluble substance) settle down at the bottom when water left for sometime.

Loading tank:- Alum is mixed with water, suspended particles in water get loaded with alum particles and settle down.

Filtration tank:- It has three layers of fine sand, coarse sand and tiny stones(gravel). When water passes through them small suspended particles is also removed.

Chlorination tank- Chlorine is added to water in tank to kill the germs. Now water is sent to home for further use.

PHYSICAL AND CHEMICAL CHANGES-

A substance is said to undergo a physical change when only the physical properties such as the shape, size, colour or state of the substance change ( occur without a change in chemical composition). No new substance is formed.

Example: Melting of ice, boiling water.

A substance is said to undergo a chemical change when a new substance with completely new properties (physical and chemical) is formed.

Example: Burning of wood or paper, souring of milk.

Question- answers:-

Question 1. Which separation techniques will you apply for the separation of

the following?

(a) Sodium chloride from its solution in water.

(b) Ammonium chloride from a mixture containing sodium chloride and

ammonium chloride.

(c) Small pieces of metal in the engine oil of a car.

(d) Different pigments from an extract of flower petals.

(e) Butter from curd.

(f) Oil from water.

(g) Tea leaves from tea.

(h) Iron pins from sand.

(i) Wheat grains from husk.

(j) Fine mud particles suspended in water.

Answer: (a) Evaporation

(b) Sublimation

(c) Filtration

(d) Chromatography

(e) Centrifugation

(f) Separating funnel

(g) Filtration

(h) Magnetic separation

(i) Winnowing

(j) Sedimentation and decantation

Question 2. To make a saturated solution, 36 g of sodium chloride is dissolved in

100 g of water at 293 K. Find its concentration at this temperature.

Answer: Mass of solute (sodium chloride) = 36 g

Mass of solvent (water) = 100 g

Mass of solution = Mass of solute + Mass of solvent

= 36 g + 100 g = 136 g

Question 3. Pragya tested the solubility of three different substances at

different temperatures and collected, the data as given below (results are given

in the following table, as grams of substance dissolved in 100 grams of water to

form a saturated solution).

What mass of potassium nitrate would be needed to produce a saturated

solution of potassium nitrate in 50 grams of water at 313 K?

(b) Pragya makes a saturated solution of potassium chloride in water at 353 K

and leaves the solution to coo! at room temperature. What would she observe

us the solution cools? Explain.

(c) Find the solubility of each salt at 293 K. Which salt has the highest solubility

at this temperature?

(d) What is the effect of change of temperature on the solubility of a salt?

Answer:

4. Which of the following materials fall into the category of “pure substance”?

(a)Ice

(b)Milk

(c)Iron

(d)Hydrochloric acid

(e)Calcium oxide

(f)Mercury

(g)Brick

(e)Wood

(f)Air.

Answer- Pure substances are:

Iron

Ice

Hydrochloric acid

Calcium oxide

Mercury

Question 5. Which of the following will show “Tyndall effect”?

(a) Salt solution (b) Milk

(c) Copper sulphate solution (d) Starch solution.

Answer: Milk and starch solution.

Question 6. Classify the following into elements, compounds and mixtures.

(a) Sodium (b) Soil (c) Sugar solution

(d) Silver (e) Calcium carbonate (f) Tin

(g) Silicon (h) Coal (i) Air

(j) Soap (k) Methane (l) Carbon dioxide

(m) Blood

Answer: Elements - Sodium, Silver, Tin, Silicon.

Compounds - Calcium carbonate , carbon dioxide ,methane.

Mixtures– Sugar solution , soil , coal ,soap , air and blood

NAUREEN