Class 9 Science Chapter 2 Notes Is Matter Around Us Pure

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Chapter 2 : Is Matter Around Us Pure

Pure: word means that there is no mixing in a substance.

But according to scientific langauage all thing are mixture of so many substances, not of single one.

That’s why they are not pure.

E.g., Milk, water, fat, etc.

Pure substances means that all elements have the same chemical properties.

A pure substance is made up of the same kind of elements.

Substance

A substance is a kind of matter that cannot be separated into other kind of matter by any physical process.

A pure substance is made up of the same kind of elements.

Types of Mixtures

It is a substance in which two or more substances (element or compound) are simply mixed together in any proportion.

Examples: The air is a mixture of oxygen, nitrogen, argon, carbon dioxide and water vapor.

Types of Mixture

Mixture is of two types:

Homogenous mixture
Heterogenous mixture

Homogenous mixture: It has no visible boundaries of separation between the various constituents, so they are called homogenous mixtures.

Example: Sugar in water. It has a uniform composition throughout its mass.

Heterogenous Mixture: These types of mixtures has visible boundaries of separation between the various constituents.

Example : Mixture of sugar and sand. It does not have a uniform composition throughout its mass.

What is a solution

Solution: A solution is a homogenous mixture of two or more substances.

E.g. Nimboo pani, soda water.

A solution has a solvent and a solute as its components.

The component of the solution that dissolves the other component in it is called the solvent.

The component of the solution that is dissolved in the solvent is called the solute.

Solution: Solute(Substance dissolved) + Solvent(Substance in which dissolved)

E.g., Sugar + Water = Sugar solution

Properties of A Solution

A Solution is a Homogeneous mixture.
The particles of a solution are smaller than 1nm (10^-9 Metre) in Diameter.they can not bean by Naked eyes.
Because of Very Small Particle Size, They do not scatter a beam of lighting passing through the solution.
The Solute Particles Cannot be seperated from the mixture by the process of filtration.

Concentration of a solution

Depending upon the amount of solute present in a solution, it can be called a dilute, concentrated or a saturated solution.

Dilute and concentrated are comparative terms.

when no more solute can be dissolved in a solution at a given temperature, it is called a saturated solution.

Any particular temperature, a solution that has dissolved as much solute as it is capable of dissolving, is said to be a saturated solution.

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

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

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

Concentration of solution = Amount of solute / Amount of solution

Amount of solute / Amount of solvent

Ways of expressing the concentration of a solution

Mass by mass percentage of a solution

Mass of solute x100

Mass of solution

Mass by volume percentage of a solution

Mass of solute x100

Volume of solution

What is a suspension?

In which solids are dispersed in liquids , are called suspensions.

A suspension is a heterogeneous mixture

Particles of a suspension are visible to the naked eye.

Properties of a Suspension

Suspension is a heterogeneous mixture.

The particles of a suspension can be seen by the naked eye.

The particles of a suspension scatter a beam of light passing through it and make its path visible.

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

WHAT IS A COLLOIDAL SOLUTION?

Thomas Graham (1861) observed that substances like gum, starch, glue, etc., in dissolved state, either do not diffuse or pass very slowly through parchment paper or animal membrane. He called such substances colloids (from Greek word Kolla meaning gum – like).

A colloidal solution is a heterogeneous mixture, for example, milk.

Because of the small size of colloidal particles, we cannot see them with naked eyes.

These particles can easily scatter a beam of visible light.

Tyndall effect

This scattering of a beam of light is called the Tyndall effect after the name of the scientist who discovered this effect.

The Tyndall effect can also be observed when a fine beam of light enters a room through a small hole.

This happens due to the scattering of light by the particles of dust and smoke in the air.

Observation of tyndall effect

The Tyndall effect can be observed when sunlight passes through the canopy of a dense forest.

In the forest, mist contains tiny droplets of water, which act as particles of colloid dispersed in air.

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 eyes.

Colloids are large 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, a colloid is quite stable.

They cannot be separated from the mixture by the process of filtration.

Dispersing medium

The components of a colloidal solution are the dispersed phase and the dispersion medium.

The solute – like component or 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.

Separating the components of a mixture

How can we obtain coloured component from Blue/Black Ink?

Evaporation:

Basic principle : Out of the two components of a mixture one can evaporate [ i.e. , has less boiling point) and other has higher boiling point.

Example: Mixture of dye [ higher boiling point ) and wate. Out of water and dye, water evaporates but the dye is left behind in petri dish.

How can we separate cream from milk?

Centrifugation:

Basic principle: When the mixture is rotated very fast, then denser particles are forced at the bottom and lighter particles stay above.

Example Separating cream from milk

Application:

( a ) Used in diagnostic labs for blood and urine tests.

(b) Used in dairies and home to separate butter from cream.

( c ) Used in washing machines dryers to squeeze out water from clothes.

How can we separate a mixture of two immiscible liquids?

Differential entraction:

Basic principle: Two immiscible liquids ( which do not dissolve in each other ) can be easily separated by putting in a differential entraction funnel / separating funnel

Example : Water from oil can be separated by first opening the stop cock till water is removed in one beaker , then afterwards oil can be collected in a separate beaker.

Applications

To separate mixture of oil and water.

In the extraction of iron from its ore, the lighter slag is removerd from the top by this method to leave the molten iron at the bottom in the furnace.

How can we separate a mixture of salt and ammonium chloride?

Sublimation

Basic principle: Out of the two components , one will sublime ( directly converts to gas from solid ) and other will not.

Example : NHCl ( ammonium chloride ) and NaClcommonsaltmixture can be easily separated by heating so that NH4CI sublimes but common salt remains behind.

Applications:

Is the dye in black ink a single colour?

Chromatography

Basic principle : Colored components of a mixture can be separated by using an adsorbent on which they are adsorbed at different rates.

When water / any suitable solvent moves up, the chromatography paper ink with two different colors separates because both colors are adsorbed at different speeds.

Applications

(a) To separate colors of a dye.

(b) To separate pigments from natural colors like chlorophyll.

How can we separate a mixture of two miscible liquids?

Distillation

Basic principle : Out of the two components one has a lower boiling point and other has higher boiling point. This is used to separate two or more miscible liquids.

Example: When mixture of acetone and water is heated, acetone having lesser boiling point, boils and moves to delivery tube, within which it condenses back to liquid with the help of a condenser clamped to it. Thus, acetone is separated out in a beaker and water is left in the distillation flask.

Note: if there are more than two components (liquids) mixed (with different boiling points) then we use a fractionating column to separate all the components from each other.

This process is done for air, petroleum etc

Petroleum is separated into paraffin wax, lubricating oil, diesel, kerosene, petrol and petrol gas by this method.

How can we obtain different gases from air?

Fractional Distillation of Air

Some of the applications of fractional distillation:

(a) In petroleum refineries , petrochemical and chemical plants . natural gas processing and cryogenic air separation plants.

(b) In oil refineries to separate crude oil into useful substances (or fractions)

(d) In the separation of oxygen, liquid nitrogen and argon from air.

How can we obtain pure copper sulphate from an impure sample?

Crystallisation

Basic principle: To remove impurities from a mixture by first dissolving in a suitable solvent and then crystallising out one component.

Example:

Copper sulphate crystals impure ) are first dissolved in sulphuric acid and then heated to saturated solution Now , this solution is left overnight.

So , only pure copper sulphate crystals are formed whereas impurities are left behind in the solution.

This solution can be thus filtered so as to get pure copper sulphate crystals on filter paper.

Why is crystallisation better than evaporation?

Some solids decompose or get charred upon heating to dryness during evaporation E.g. sugar.
Some impurities remain dissolved in solution after filteration. On evaporation , these impurities do not evaporate and remain with the mixture.

Applications

Purification of salt from sea water.
Separation of crystals eg , alum ( phitkari , copper sulphate ) from their impure crystals.

Physical and Chemical Changes

Chemical change

Not Easy Reverse

New Product (S) Formed

Reafants Used Up

Often Heat /Light/Sound/ Fizzing occurs

Electricity may be produced

A precipitate may form

Ex wood burning

Physical change

Easily reversible

No New Products

Often Just a State Change

Ex Ice melting

What are the type of pure substances?

Elements

Robert Boyle A was the first scientist to use the term element in 1661.

Antoine Laurent Lavoisier (1743–94), a French chemist, was the first to establish an experimentally useful definition of an element.

Elements can be normally divided into metals, non – metals and metalloids.

Metals

Metals usually show some or all of the following properties:

They have a lustre (shine).

They have silvery – gray or golden – yellow colour.

They conduct heat and electricity.

They are ductile (can be drawn into wires).

They are malleable (can be hammered into thin sheets ).

They are sonorous (make a ringing sound when hit).

Examples of metals are gold, silver, copper, iron, sodium, potassium etc.

Mercury is the only metal that is liquid at room temperature.

Non metals

Non – metals usually show some or all of the following properties:

They display a variety of colors.

They are poor conductors of heat and electricity.

They are not lustrous, sonorous or malleable.

Examples of non – metals are hydrogen. oxygen, iodine, carbon (coal, coke). bromine, chlorine etc.

Metalloids

Metallaoids have intermediate properties between of metals and non – metals.

Metalloids: examples are boron, silicon, germanium etc.

Mixture and compound

Mixture	Compound
1. Elements or compounds are simple calling so new substance is formed. Compound	1. Substances Are Reated Together with each other to make a new substance.
2. Elements do not combine in a fixed ratio.	2. Compositions the the component is Fixed i.e. , They combine together in a fixed ratio according to their masses.
3. A mixture shows the properties of its components	3. compound does not show the Properties of component elements.
4. Components can be easily separated by any mechanical method which is suitable.	4. components can not be separated from each other by simple mechanical methods.
Example: Mixture of iron and sulphur.	Example: iron and sulphur react to form iron sulphide

Benefits of NCERT Class 9 Science Chapter 2 Notes Is Matter Around Us Pure

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