Vidyarthi Academy

Home NCERT Solutions Chapter Notes Test Papers Contact Us

CBSE NOTES CLASS 9 SCIENCE CHATER 2

IS MATTER AROUND US PURE

Pure Substances

Mixtures

Types of Mixtures

Homogeneous Mixtures

Heterogeneous Mixtures

Alloys

Solution

Solvent

Solute

Properties of a solution

Concentration of a Solution

Saturated Solution

Solubility

Unsaturated Solution

Concentration

Suspension

Properties of a Suspension

Colloidal Solution

Properties of a colloid

Tyndall Effect

Components of Colloidal

Dispersion Medium

Dispersed Phase

Types of Colloids

Physical Properties

Physical Change

Chemical Change

Types of Pure Substances

Elements

Properties of Metals

Properties of Non-Metals

Metalloids

Compounds

Separating the Components of a Mixture

1. Evaporation – Separating Coloured Component (Dye) From Blue/Black Ink

2. Centrifugation - Separating Cream From Milk

3. Separating Funnel - Separatig A Mixture of Two Immiscible Liquids

4. Sublimation

5. Chromatography

6. Distillation - Separating A Mixture of Two Miscible Liquids

7. Fractional Distillation

Separation of Different Gases from Air

8. Crystallistion

Purification of Water

CBSE NOTES CLASS 9 SCIENCE CHATER 2

IS MATTER AROUND US PURE

Pure Substances

A pure substance consists of a single type of particles. It means that all the constituent particles of that substance are the same in their chemical nature.

Examples – Sodium, Nitrogen gas, Sugar etc.

Mixtures

Mixtures are constituted by more than one kind of pure form of matter, known as a substance. That is a mixture contains more than one substance.

Mixtures can have variable composition.

Examples – Milk, Soft drinks etc.

Types of Mixtures

Homogeneous Mixtures

Mixtures, which have physically uniform compositions, are called homogeneous mixtures.

Examples – Solution of Potassium Permanganate in water, Solution of sugar in water, Salt in water, Copper Sulphate in water etc.

Alloys

Alloys are homogeneous mixtures of metals and cannot be separated into their components by physical methods. But still, an alloy is considered a mixture because it shows the properties of its constituents and can have variable composition. For example, brass is a mixture of approximately 30% zinc and 70% copper.

Heterogeneous Mixtures

Mixtures, which contain physically distinct parts and have non-uniform compositions, are called heterogeneous mixtures.

Examples - Mixture of sodium chloride and iron filings, salt and sulphur, oil and water.

Solution

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

A solution has two components - a solvent and a solute.

Solvent - The component of the solution that dissolves the other component in it (usually the component present in larger amount) is called the solvent.

Solute - The component of the solution that is dissolved in the solvent (usually present in lesser quantity) is called the solute.

Examples

Properties of a solution

Concentration of a Solution

In a 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 a saturated solution.

Dilute and concentrated are comparative terms.

Saturated Solution

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

Or

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

Solubility

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

Solubility of solids in liquids increases with increase in temperature.

If a saturated solution is cooled, the solute crytallises.

Different substances in a given solvent have different solubilities at the same temperature.

Unsaturated Solution

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

Concentration

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.

Mass by mass percentage of solution = Mass of solute Mass of solution×100

Mass by volume percentage of solution = Mass of solute Volume of solution×100

Suspension

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

Colloidal Solution

A colloidal solution is a heterogeneous mixture in which a substance is evenly dispersed or suspended throughout another substance. It is also known as colloidal suspension, or colloid.

Due to the relatively smaller size of particles as compared to that of a suspension, the mixture appears to be homogeneous. But actually, a colloidal solution is a heterogeneous mixture.

Example - milk.

Properties of a colloid

Tyndall Effect

The scattering of a beam of light by particles of colloid or fine suspension is called the Tyndall effect. This makes the path of the light beam visible.

It is named after the scientist who discovered this effect.

Vidyarthi Academy

Components of Colloidal

There are two components of colloidal solution,

Dispersed Phase – The solute-like component or 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.

Types of Colloids

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

Dispersed phase

Dispersing Medium

Type

Example

Liquid

Gas

Aerosol

Fog, clouds, mist

Solid

Gas

Aerosol

Smoke, automobile exhaust

Gas

Liquid

Foam

Shaving cream

Liquid

Liquid

Emulsion

Milk, face cream

Solid

Liquid

Sol

Milk of magnesia, mud

Gas

Solid

Foam

Foam, rubber, sponge, pumice

Liquid

Solid

Gel

Jelly, cheese, butter

Solid

Solid

Solid Sol

Coloured gemstone, milky glass

Physical Properties

The properties that can be observed and specified like colour, hardness, rigidity, fluidity, density, melting point, boiling point etc., are the physical properites.

Physical Change

The change which occurs without changing the composition and the chemical nature of the substance is called physical change. No new substance is formed.

Example - change of state.

Chemical Change

Chemical change is any change that results in the formation of new chemical substances. During this process one substance reacts with another to undergo a change in chemical composition.

Example – burning of paper.

During burning of a candle, both physical and chemical changes take place. First the wax melts and evaporates and then the vapour burns.

Types of Pure Substances

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

Elements

An element is a basic form of matter that cannot be broken down into simpler substances by chemical reactions.

Elements are classified as metals, non-metals and metalloids.

Properties of Metals

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

Properties of Non-Metals

Examples - hydrogen, oxygen, iodine, carbon (coal, coke), bromine, chlorine etc.

Metalloids

Elements having intermediate properties between those of metals and non-metals, are called metalloids; examples are boron, silicon, germanium etc.

Compounds

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

Examples – Water, Copper Sulphate etc.

Mixture and Compounds

Mixtures

Compounds

  1. Elements or compounds just mix together to form a mixture and no new compound is formed.
  1. Elements react to form new compounds.
  1. A mixture has a variable composition.
  1. The composition of each new substance is always fixed.
  1. A mixture shows the properties of the components.
  1. The new substance has totally different constituent substances.
  1. The constituents can easily be separated by physical methods.
  1. The constituents can be separated only by chemical or electrochemical reactions.

Summary Classification of Matter

Vidyarthi Academy

Separating the Components of a Mixture

Different methods of separation are used to get individual components from a mixture.

Heterogeneous mixtures can be separated into their respective constituents by simple physical methods like handpicking, sieving, filtration etc.

Some Special Techniques

1. Evaporation – Separating Coloured Component (Dye) From Blue/Black Ink

Evaporation is the process by which water (and other liquids) changes from a liquid state to a vapor or gas state.

We can separate the volatile component (solvent) from its non-volatile solute by the method of evaporation.

The process involves heating the solution until the solvent evaporates (turns into gas) leaving behind the solid residue.

Acivity

Vidyarthi Academy

2. Centrifugation - Separating Cream From Milk

Mixtures like milk have very small solid particles in a liquid, which pass through a filter paper, hence filtration technique cannot be used for separation.

Such mixtures are separated by centrifugation. The principle is that the denser particles are forced to the bottom and the lighter particles stay at the top when spun rapidly.

Applications

3. Separating Funnel - Separatig A Mixture of Two Immiscible Liquids

Vidyarthi Academy

A separating funnel is a cone shaped glass container with a hemispherical end. It has a stopper at the top and stopcock(tap), at the bottom.

If a mixture of two immiscible liquids is allowed to stand undisturbed for some time, the two liquids settle in two separate layers, depending on the densities. The denser liquid makes lower layer and lighter makes the upper layer.

We can separate the liquids by opening the stopcock of the separating funnel and pour out the lower layer of liquid carefully and closing it as soon as the upper layer reaches the stopcock.

Applications

4. Sublimation:

Some of the solids like ammonium chloride change directly from solid to gaseous state on heating.

To separate mixtures which contain a sublimable volatile component (like ammonium chloride) with non-sublimable impurity ((like salt), the sublimation process is used

Some examples of solids which sublime are ammonium chloride, camphor, naphthalene, iodine and anthracene.

Activity

  1. Take the mixture of sublimable and non-sublimable substance in a china dish.

  2. Put an inverted funnel on the china dish. Closes the end of the funnel with the help of a cotton plug, so that the gas does not escape.

  3. Heat the china dish using a bunsen burner.

  4. The sublimable substance rises as a gas and solidifies at the neck of the funnel.

  5. We can remove the funnel and scratch the solid substance away.

Vidyarthi Academy

5. Chromatography: Chromatography is the technique used for separation of those solutes that dissolve in the same solvent.

Example – Separating Different Colours from Ink.

Usually, a dye (ink) is a mixture of two or more colours.

The ink has water as the solvent and the dye is soluble in it.

Activity:

We use a thin strip of filter paper marked with ink.

Lower it in a beaker, containing water, so that the drop of ink on the paper is just above the water level and is left undisturbed for some time.

As the water rises on the filter paper it takes along with it the dye particles.

The coloured component, that is more soluble in water, rises faster and in this way the colours get separated.

Vidyarthi Academy

Applications

To separate,

6. Distillation - Separating A Mixture of Two Miscible Liquids

The process of simple distillation is used for the separation of components of a mixture containing two miscible liquids that boil without decomposition and have sufficient difference (> 25 oK) in their boiling points.

Vidyarthi Academy

Example – Mixture of acetone and water.

The apparatus consists of three major parts:

(i) A distillation flask, which is a round bottomed flask to heat the mixture and volatilize the components,

(ii) A condenser to cool the vapours back to liquid state,

(iii) A collection vessel

7. Fractional Distillation

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

Example - Separation of different gases from air, different factions from petroleum etc.

Vidyarthi Academy

The apparatus is similar to that for simple distillation, except that a fractionating column is fitted in between the distillation flask and the condenser.

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

Separation of Different Gases from Air

Air is a homogeneous mixture and can be separated into its components by fractional distillation.

The flow diagram shows the steps of the process.

The air is compressed by increasing the pressure and is then cooled by decreasing the temperature to get liquid air.

This liquid air is allowed to warm-up slowly in a fractional distillation column, where gases get separated at different heights depending upon their boiling points.

Vidyarthi Academy

Vidyarthi Academy

8. Crystallistion

Crystallisation is a process that separates a pure solid in the form of its crystals from a solution.

The solid, which has impurities is dissolved in a liquid and made a solution.

The solution is warmed in an open container, allowing the solvent to evaporate, leaving a saturated solution.

As the saturated solution is allowed to cool, the solid will come out of the solution and crystals will be formed.

The crystals can then be collected and allowed to dry.

The size of crystals depends on the rate of cooling.

Fast cooling will result in a large number of small crystals. Slow cooling will result in a few crystals of large size.

Crystallisation technique is better than simple evaporation technique as,

Applications

Purification of Water

Vidyarthi Academy

Water purification is the process of removing undesirable chemicals, biological contaminants, suspended solids and gases from contaminated water. The goal is to produce water fit for human consumption (drinking water).

The process involves Sedimentation, Filteration and Chlorination.

Solids in the water, such as leaves and soil, are removed.

Different-sized insoluble solids are removed as the water trickles through the filter beds. These are cleaned often by pumping clean water backwards through the filter.

The water is passed into a sedimentation tank.

The water is passed through specially-prepared layers of sand and gravel called filter beds. The water is then passed through a fine filter, such as carbon granules, to remove very small particles.

Chlorine is added to drinking water to sterilise it.

The chlorine kills microbes - including microbes that cause diseases such as typhoid, cholera and dysentery.