CBSE Class 9 Science Revision Notes Chapter 2

CBSE Class 9 Science Revision Notes Chapter 2 – Is Matter Around Us Pure

All observable phenomena are built on matter and energy. In other words, as described in Class 9 Science Chapter 2 Notes, matter is anything that occupies space and has mass. Matter is composed of two elementary particles known as leptons and quarks. It is classified into two types: pure substances and mixtures. While pure substances are composed of a single type of particle, mixtures are composed of more than one type of particle.

Comparison among the Properties of Metals and Non-Metals:

Metals Non-Metals
1. Metals are durable and long-lasting since they have extremely high tensile strength. 1. Non-metals that don’t last very long are less durable. Their tensile strength is average.
2. Metals are lustrous (bright) and can be polished.  2. Non-metals appear dull and cannot be polished (except iodine, which is a lustrous non-metal).
3. At normal temperatures, metals are solids (except mercury, which is a liquid metal). 3. At normal temperatures, non-metals are usually solids or gases (except bromine, which is a liquid non-metal).
4. Metals are exceptional conductors of heat and electricity. 4. Non-metals are poor heat and electrical conductors (with the exception of graphite, which is a good conductor of electricity, and diamond which is a good thermal conductor).
5. Metals are malleable and ductile. Metals can be drawn into fine wires and hammered into thin sheets using this method. 5. Non-metallic materials are brittle. They are neither ductile nor malleable.

The Distinction Between Compounds and Mixtures:

Compounds Mixtures
A compound is made up of two or more  chemically joined components. Instead of being chemically combined, two or more elements or compounds are simply blended into the mixture.
A compound’s elements are present in a set mass ratio. This proportion will remain constant. A mixture’s ingredients are present in a predetermined ratio. It varies from mixture to mixture.
Compounds are always homogeneous, which means that their composition is consistent throughout. Mixtures can be either homogeneous or heterogeneous.
The identities of elements in a compound are lost, i.e. the features of the constituting elements are not visible in the compound. A mixture’s constituents don’t lose their identities, i.e., a mixture exhibits all the constituents’ qualities. There is no energy change observed during the development of a mixture.
It is impossible to physically separate parts of a compound. It is easy to physically separate the constituents of a combination.

Class 9 Science Chapter 2 Notes

Chapter 2 Science Class 9 Notes: Mixture and its Types

A mixture is made up of two or more pure substances that can be isolated physically.

There are two types of mixtures:

  1. Homogenous Mixture: A homogenous mixture is one in which all the components present in it are well mixed and there are no boundaries of separation between them. For example, sugar in water.
  2. Heterogeneous Mixture: A heterogeneous mixture is one in which all the components are not mixed in the same proportion and there are visible boundaries of separation between them. For example, sand in water.

Class 9 Science Chapter 2 Notes: Solution And its Properties

A solution, according to Chapter 2 Class 9 Science notes, is a homogeneous mixture of more than one substance. For example, soda water, lemonade, and so on.

Any solution contains two components: solvent and solute.

  1. Solvent – A solvent is a component of any solution in which solute particles are dissolved.
  2. Solute – A solute is a component of any solution that is dissolved in the solvent.

Science Class 9 Chapter 2 Notes: Points to Remember

  • Another name given to homogenous mixture is ‘solution’.
  • Any solution particle is less than 1 nm in diameter and cannot be seen with the naked eye.
  • It cannot disperse a light beam that travels through it. As a result, the path is not visible in a solution.
  • Filtration makes it impossible to separate solute particles from a mixture.
  • A solution is very stable, and when left undisturbed, the solute particles in a solution cannot settle.

Class 9 is Matter Around Us Pure Notes: Types of Solution & Concentration

The concentration of a solution refers to the amount of solute present in it. The concentration of a solution is the amount of solute that can dissolve in a given volume or mass of solvent.

  1. a) Suspension and its Properties

Any heterogeneous mixture in which any solute particle cannot dissolve but remains suspended in the bulk of the specific medium is referred to as a suspension. For instance, when chalk is mixed with water, smoke is released into the air.

Properties:

  • It is a heterogeneous mixture.
  • With the naked eye, one can observe particles.
  • The size exceeds 100 nm.
  • If a solution is passed through it, the solvent and solute can be separated.
  1. b) Colloidal Solution and its Properties

A colloidal solution is a heterogeneous mixture in which the particle size is intermediate between suspensions and true solutions. They can easily scatter a visible light beam. This is referred to as the Tyndall effect.

Properties:

  • Particles are invisible to the naked eye.
  • Filtration cannot separate solvents and solutions.
  • The particles have a size of less than 100 nm.
  • It is a stable mixture.
  • When particles are not disturbed, they do not settle.

Class 9 Science Chapter 2 Notes: Separations of the Components of Mixtures

To extract a specific component from a mixture, several methods are used. Heterogeneous mixtures can be separated using physical methods, such as sieving, handpicking, filtration, and so on.

Changes in Physical and Chemical Properties

A physical change is any process that results in a change in physical property but does not produce any new substance. Changes in rigidity, colour, density, fluidity and boiling point are all examples of common physical changes.

Chemical changes refer to the process of creating a new chemical substance. Inflammability and odour are two chemical properties.

Class 9 Chapter 2 Science Notes explains physical and chemical changes. According to the definition, a pure substance can be an element or a compound. A substance that cannot be divided into simpler substances is known as an element. A compound is any substance formed by the combination of more than two elements.

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FAQs (Frequently Asked Questions)

1. What are pure and impure materials?

A pure material contains only one type of particle. A pure material, in other words, is a single isolated form of matter. It contains only one type of component, rather than several. When we look around, we can see that most of what we see is made up of combinations of two or more individual elements, such as seawater, minerals, and dirt. A pure substance has a constant composition every time, as well as a constant melting and boiling point. 

Impure substances are those composed of two or more types of particles (atoms or molecules) that can be separated physically. Mixtures’ constituents are all impure. Some examples of mixtures include salt solution, sugar solution, milk, seawater, air, sugarcane juice, soft beverages, sharbat, rocks, minerals, petroleum, LPG, biogas, tap water, tea, coffee, paint, wood, soil, bricks. It is possible for the mixture to be homogeneous or heterogeneous. The composition of a mixture, as well as its melting and boiling points, are not fixed.

2. Name two components of a colloidal solution.

A colloidal solution has two components: dispersing medium and dispersed elements. Milk, for example, is a colloidal solution. It contains suspended casein (protein) micelles with a hydrophobic core.

3. What does Class 9 Science Chapter 2 "Is Matter Around Us Pure" cover?

We find several items around us every day, such as water, which we drink; salt, which we add to meals for flavour; milk, which we drink because it contains calcium and other minerals; soap, which we use to wash our clothing; paint, which we use to paint walls; and so on. The composition and characteristics of these things differ. They could be completely pure or contain contaminants. All of these properties of matter will be discussed in this chapter.

4. What are the differences between homogenous and heterogenous mixtures?

The distinction is as follows:

Homogeneous Mixture: A homogeneous mixture is one in which all the components are well blended and there are no separation limits between them. Special techniques can be used to separate them. For example, sugar in water. Heterogeneous Mixture: A heterogenous mixture is one in which all of the components are not mixed in the same proportion and have visible separation boundaries. For example, sand in water.

5. What is suspension and what are its properties?

A suspension is any heterogeneous mixture in which any solute particle cannot dissolve but remains suspended in the majority of the medium. For example, when chalk is mixed with water and thrown into the air, smoke is produced.

Properties:

  • It is a diverse combination.
  • Particles are not extremely small.
  • The size exceeds 100 nanometers.
  • If a solution is passed through it, the solvent and solute may separate.

6. What determines whether a solution is concentrated, saturated, or diluted?

The concentration of a solution is determined by the amount of solute that can dissolve in a solution at a given temperature while keeping the pressure constant. Solutions can be concentrated, diluted, saturated, or oversaturated. All of these solution types’ properties and separation methods are explained in the Is Matter Around Us Pure Class 9 Notes.

7. Describe the characteristics of a compound.

The characteristics of a compound are as follows:- 

  • The constituents of a pure compound are the same.
  • The properties of a pure compound differ significantly from the properties of the element from which it is formed.
  • Because a compound is formed through a chemical process, it has properties distinct from the elements from which it is formed. For example, hydrogen gas is combustible, but oxygen promotes combustion. The chemical interaction between the two gases produces water as a byproduct. It is not combustible and cannot be burned. Water is distinct from the other two in that it puts out fire.
  • It terminates or extinguishes combustion. Water is frequently used to extinguish fires.
  • The constituents of chemical compounds cannot be separated mechanically. To form a compound, the energy exchange is required.
  • Water has been classified as a compound due to the following factors: Water cannot be separated into its constituents, hydrogen and oxygen, using physical methods.
  • Heat and light are produced when hydrogen and oxygen are burned to create water. Water’s chemical composition is constant.
  • The components hydrogen and oxygen have a mass ratio of 1:8.
  • Water has a stable boiling point of 100 C (or 373 K ) (or 760 mm ) at 1 atmosphere of atmospheric pressure.