Notes Class 9 Science Chapter 2 Is Matter Around Us Pure

Notes For All Chapters Science Class 9 CBSE

MATTERS :-

Anything which occupies space and has mass is called matter.

Matter can be divided in two categories.

( I ) Pure Substance
( II ) Impure Substances (Mixtures)

( I ) Pure Substance :-

Pure substances means that all elements have same chemical properties. A pure substance is made up of same kind of elements.

Pure :- ‘Pure’ word means that there is no mixing in a substance. But according to scientific language all things are mixture of so many substances, not of single one. That’s why they are not pure. E.g. Milk, water, fat, etc.

Substance :- A substance is a kind of matter that cannot be separated into other kind of matter by any physical process. Apure substance is made up of same kind of elements.

What is a Mixture?

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, carbon dioxide and water vapour.

Types of Mixture :-

• Mixture is of two types :

Homogenous mixture
Heterogenous mixture

1. Homogenous Mixture :-

These types of mixtures have no visible boundaries of separation between the various constituents.

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

        2. Heterogenous Mixture :-

These types of mixtures have visible boundaries of separation between the various constituents.

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

Differences between Homogeneous and Heterogeneous :-

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.

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

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

Properties of a Solution :-

• A solution is a homogenous mixture.
• We cannot see the particles of a solution through naked eyes as they as are small as 1 nanometer in diameter.
• The path of light is not visible through the solution. The particles of a solution do not scatter light through them as they are extremely small.
• We cannot separate the particles of a solution by methods of filtration.

 Concentration of a solution :-

Saturated solution :- When no more amount of solute can be dissolved in a solution at a given temperature, it is called a saturated solution.

Unsaturated solution :- When more amount of solute can be dissolved in a solution at given temperature, it is called a saturated solution.

Solubility :- The amount of the solute present in the saturated solution at the given temperature is called its solubility.

Concentration :-

• Concentration refers to the amount of a substance per defined space or can be defined as the ratio of solute in a solution to either solvent or total solution.

Two methods of finding concentration of solution :-

• Mass by mass percentage of a solution = (Mass of solute/Mass of solution) x100
• Mass by volume percentage of a solution = (Mass of solute/Volume of solution) x100

Suspension :-

• suspension is formed when two or more substances non-uniform manner. Heterogeneous mixtures are suspensions. The solute does not mix with the solvent and can be viewed through naked eyes.

Properties of Suspensions :-

• A suspension is a heterogeneous mixture.
• We can see the particles of suspensions through naked eyes.
• We can see the path of light through the particles of a suspension.
• The particles of suspension tend to settle down when left undisturbed. Then, they can be separated using filtration.

Colloidal solutions :-

A colloidal solution or a colloid is a uniform solution of two or more substances. The particles are relatively very small that the solution appears as a homogeneous mixture but it is not.

Properties of colloids :-

• Colloids are heterogeneous in nature.
• The particles of a colloid cannot be seen through naked eyes.
• The particles scatter a beam of light passed through a colloid and produce Tyndall effect.
• Colloids are stable in nature. The particles of colloids do not settle down if left uninterrupted.
• We cannot separate the particles of a colloid through filtration. We use a method called Centrifugation to separate the particles of a colloid.

Tyndall Effect :-

When a beam of light is passed through a colloid the particles of the colloid scatter the beam of light and we can see the path of light in the solution.

• For Example :- when a ray of light enters a dark room it is scattered by the dust particles present in the air and we can see the path of light clearly.

Methods of Separation of Mixtures :-

Evaporation :-

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

Centrifugation :-

• Basic principle :- Separation of Substances or particles on the basis of their density, when mixture is rotated very fast, then denser particles are forced at the bottom and lighter particles stay above.

• Applications :-

1. Used in diagnostic labs for blood and urine tests.
2. Used in dairies and home to separate butter from cream.
3. Used in washing machines dryers to squeeze out water from clothes.

Separating Funnel :-

• Basic principle :- Two immiscible liquids (which do not dissolve in each other) can be easily separated by putting in a separating funnel.
• Applications :-

Separation of oil from water.

Extraction of iron from its ore. Lighter slag is removed from above the molten iron.

Sublimation :-

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

Applications :- Camphor, naphthalene, anthracene, NH,Cl can sublime.

Chromatography :-

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

Applications :-

• To separate colours of a dye.
• To separate pigments from natural colours like chlorophyll.
• To separate drugs from blood.

Distillation :-

Basic principle :- Based on Separating mixture of miscible liquids having different boiling points, followed by condensation. 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.

Applications

• In petroleum refineries, petrochemical and chemical plants, natural gas processing and cryogenic air separation plants.
• In oil refineries to separate crude oil into useful substances (or fractions).
• In the separation of oxygen, liquid nitrogen and argon from air.

Crystallisation :-

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

• Applications :-

1. Purification of salt from sea water.
2. Separation of crystals [e.g., alum (phitkari), copper sulphate] from their impure crystals.

Physical Properties :-

• Properties of a substance such as rigidity, colour, fluidity, boiling point, melting point, density and hardness which we can observe are called as Physical Properties.

Physical Change :-

• When physical properties of a substance change it is known Physical Change. When we convert a substance from one state to another, such as a solid into a liquid or vice-versa, it is also a physical change as only the physical nature of the substance changes without affecting its chemical nature.
•  For Example :- Change of ice into water. The chemical properties of water remain the same.

Chemical Change :-

•  When the chemical properties or chemical composition of a substance gets altered it is called a chemical change. It is also called as a Chemical Reaction.
• For Example :- Burning of paper

Elements :-

1. An element is the simplest form of matter. Elements cannot be broken down into further elements by chemical reactions.
2. Elements are further characterized as Metals, Non-Metals and Metalloids

 Metals :- Silver, Mercury, Copper, Gold

• Metals are lustrous (shiny)
• Metals conduct heat and electricity
• Metals have a silver-grey or gold-yellow colour
• We can hammer metals and form thin sheets (Malleability)
• We can convert metals into wires (Ductility)
• Metals always produce a ringing sound if they are hit (Sonorous)

Non-Metals :- Carbon, lodine, Chlorine, Oxygen, Hydrogen

• Non-Metals do not conduct heat and electricity
• Non-Metals are not sonorous, lustrous or ductile
• Non-Metals have varied colours

Metalloids :- Silicon, Germanium

They show some properties of metals and some of the non-metals.

Compounds :-

• It is a substance that consists of two or more substances. These substances are combined chemically with each other in fixed proportions. The properties of a compound are different than that of its constituents.
• For Example :- Ammonium Sulphate, Sulphur Chloride, Water.

Difference between Mixtures vs. Compounds :-