Is matter around us pure class 9 notes- Chapter 2

 Is matter around us pure class science 9 notes- Chapter 2

Table of Contents -

1. Introduction

      1.1 What are pure substances?

2. Types of pure substances?

     2.1 Elements

            2.1.1 Metals

            2.1.2 Non-metals

            2.1.3 Metalloids

    2.2 Compounds

3.  What is mixtures?

     3.1 Types of mixtures

4. What is solution?

     4.1 Properties of solution

     4.2  Concentration of solution

5. Suspension

     5.1 Properties of suspension

6. Colloidal solution

     6.1 Properties of colloidal solution

7. Physical and Chemical changes

Introduction- 

As we have discussed in the previous chapter everything around us is made of matter and matter has both mass and volume. Matter is made up of extremely small particles.
Are all the substances in pure form? Or What are pure substances?
Pure substances are those which consist of a single type of particles. 

Types of pure substances-

On the basis of chemical composition, substances are of two types elements and compounds

Element-

• An element is a substance that cannot be split into two or more simpler substances by chemical methods ( such as heat, light, or electric energy).

• An element consists solely of atoms of the same kind.

• All the elements can be divided into 3 groups-  Metals, non-metals, and metalloids.

Metals- 

• They are lustrous ( shiny).
• They are great conductors of heat and electricity.
• They are malleable which means they can be beaten into thin sheets on hammering.
• They are ductile which means they can be drawn into thin wires on stretching.
• They are sonorous which means they produce a ringing sound on hitting the metals.
• Ex- gold, silver, copper, sodium, potassium, iron, etc.

Non-metals-

• They are not lustrous ( shiny).
• They exhibit low conductivity when it comes to heat and electricity.                   
• They are not malleable, ductile, or sonorous.
• Ex- hydrogen, bromine, iodine, phosphorus, sulfur, etc.

Metalloids -

• The elements which show intermediate properties of both metals and non-metals are called metalloids.
• They are neither conductors of electricity like metals, nor insulators like non-metals, they are often called semiconductors.
• Ex- germanium, silicon, boron, etc.

Compounds-

• A compound is a substance made up of two or more elements that are chemically bound.
• The composition of a compound is fixed, which means the compound has a definite formula.
• A compound has a fixed melting point, boiling point,  etc.
• A compound cannot be separated into its constituents by physical means( methods).

What is mixtures?

Mixtures are formed by adding more than one kind of pure form of matter. For ex- salt is dissolved in water to form salt water which is a mixture.

Note - A mixture can be separated by physical means into its pure substances. 

Types of mixtures-

Mixtures are of three types- solutions, suspension, and colloidal solutions.

What is a solution?

A solution is a homogenous mixture that is formed by two or more substances. A homogenous mixture means the mixture is evenly spread throughout (dissolves with each other). For ex- sugar in water, air ( a mixture of gases), soda water, etc.

A solution has two components-

1. Solute- the minor component that is dissolved in the solvent.
2. Solvent- the major component on which the other component is dissolved.

Properties of solution -

• The solution is a homogenous mixture.
• The size of a solute particle is less than 1 nm. ( extremely small).
• The solutions are very stable because particles of solute do not settle down when left undisturbed.
• The solution does not show the Tyndall effect i.e. scattering of a beam of light.

Concentration of solution-

• The concentration of a solution is defined as the amount (mass or volume ) of solute present in a given amount ( mass or volume ) of solution.
• Dilute solution- in which the amount of solute is very low.
• Concentrated solution- in which the amount of solute is very high.
• Saturated solution- a solution in which no more solute can further be dissolved at a particular temperature.
• Unsaturated solution- a solution in which more quantity of solute can be dissolved at a particular temperature.
• Solubility- the amount of a solute in a saturated solution at a certain temperature represents its solubility.

Suspension-

A suspension is a heterogeneous mixture in which the solute particles are spread throughout a medium without dissolving. For example sand in water, oil in water, soot in air, etc.

Properties of suspension-

• A suspension is a heterogeneous mixture.
• The size of solute particles is more than 100nm.
• The suspension is unstable because solute particles settle down when left undisturbed for some time.
• Suspension shows the Tyndall effect.

Colloidal solution-

A colloidal solution is heterogeneous but appears to be homogenous due to two reasons one is the size of the solute particle is between the size of the solute in solution and suspension and the second is, that it is uniformly spread throughout the solution.

Properties of colloids -

• A colloidal solution is heterogeneous but appears to be homogenous.
• The size of solute particles ranges between 1 nm to 100 nm.
• The particles of colloids are quite stable because particles of a colloid do not settle down.
• The colloidal solution shows the Tyndall effect.

Physical and Chemical changes-

Physical changes- those changes in which no new substances are formed, and they can be easily returned to their original form by some physical processes. For ex-  freezing of water, melting of ice, and boiling of water all are physical changes because no new substance is formed only the water is changed into different forms i.e. ice, water, and steam respectively.

Chemical changes- in which new substances are formed and which be cannot returned to their original form. For ex- burning of paper, formation of curd from milk, cooking, etc.

    

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