NCERT CBSE Class 9 Science Chapter 2 Notes: Is Matter Around Us Pure? (Free PDF) 

We have prepared well-written NCERT CBSE Class 9 Science Chapter 2 ‘Is Matter Around Us Pure?” Notes for you. These notes are written in such a manner as to facilitate easy memorising of chapters and will serve as a method of quick revision to help you ace your exams. Let us explore them now! 

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Explore Notes of all the Chapters of Class 9 Science: 

Chapter 1	Chapter 2	Chapter 3	Chapter 4	Chapter 5	Chapter 6
Chapter 7	Chapter 8	Chapter 9	Chapter 10	Chapter 11	Chapter 12

Introduction to NCERT CBSE Class 9 Science Chapter 2 Notes ‘Is Matter Around Us Pure?’

In NCERT CBSE Class 9 Science Chapter 2 Notes, we will learn about mixtures. Proceeding forward, we will study solutions, suspensions and colloids. Then we will understand the difference between pure elements and compounds. Let us begin! 

NCERT CBSE Class 9 Science Chapter 2 Notes: Mixture and Solution

In this part of NCERT CBSE Class 9 Science Chapter 2 Notes, we have definitions and characteristics of mixture and solution. 

What is a Mixture?

When two or more substances combine in any ratio, then the formed substance is called a mixture. In a mixture, the components can be easily separated by various methods. 

Also Read: 10 Scientific Experiments That Were Ahead Of Their Time 

What is a Solution? 

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

Characteristics of a solution: 

• A solution is a homogeneous mixture. 
• The particles of a solution are smaller than 1 nm in diameter. So, they cannot be seen by the naked eye. 
• The path of light is not visible in a solution. Because of very small particle size, they do not scatter a beam of light passing through the solution. 
• The solute particles cannot be separated from the mixture by the process of filtration. 
• The solute particles do not settle down when left undisturbed, that is, a solution is stable. 
• Solutions don’t necessarily have to mean a liquid having other solid, liquid or gas dissolved in it. 
• Solutions can be of solids as well like alloys and of gases as well such as air. 
• In a solution, there is homogeneity at the particle level. For example, lemonade tastes the same throughout. This shows that particles of sugar or salt are evenly distributed in the solution. 
• A solution has a solvent and a solute as its component. 

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

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

Types of Solutions:

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 dilute, concentrated or saturated solution. 

At a given temperature, when no more solute can be dissolved in a solution, then it is said to be a saturated solution. The amount of solute present in the 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.

Concentration of a Solution:

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

The concentration of a solution can be depicted in three below-mentioned ways: 

Mass by mass Percentage of a Solution = (Mass of solute / Mass of Solution) × 100  Mass by Volume Percentage of a Solution = (Mass of Solute / Volume of Solution) x 100  Volume by Volume Percentage of a Solution = (Volume of Solute / Volume of Solution) x 100

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NCERT CBSE Class 9 Science Chapter 2 Notes: What is a Suspension? 

A suspension is a heterogeneous mixture in which the solute particles do not dissolve but remain suspended throughout the bulk of the medium. Particles of a suspension are visible to the naked eye. 

Characteristics 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. 
• They can be separated from the mixture by the process of filtration. When the particles settle down, the suspension breaks and it does not scatter light any more. 

NCERT CBSE Class 9 Science Chapter 2 Notes: What is a Colloidal Solution? 

A colloidal solution is a heterogeneous mixture of particles that are uniformly spread throughout the solution. Due to the relatively smaller size of particles, as compared to that of a suspension, the mixture appears to be homogeneous actually it is heterogeneous. It can scatter the beam of light.  

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

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. 

Characteristics of a colloid: 

• A colloid is a heterogeneous mixture. 
• The size of the particles of a colloid is too small to be individually seen with the naked eye. 
• Colloids are big 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. But, a special technique of separation known as centrifugation, can be used to separate the colloidal particles. 
• 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. 

Dispersed Phase	Dispersing Medium	Term	Examples
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

Also Read: Chemistry in Everyday Life 

NCERT CBSE Class 9 Science Chapter 2 Notes: Physical and Chemical Changes 

The properties that can be observed and specified like colour, hardness, rigidity, fluidity, density, melting point, boiling point etc. are the physical properties. The interconversion of states is a physical change because these changes occur without a change in composition and no change in the chemical nature of the substance. 

It is this chemical property of a substance that makes it different from the other. Burning is a chemical change. During this process, one substance reacts with another to undergo a change in chemical composition. Chemical change brings change in the chemical properties of matter and we get new substances. A chemical change is also called a chemical reaction. 

NCERT CBSE Class 9 Science Chapter 2 Notes: What are the Types of Pure Substances? 

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

Elements 

Robert Boyle 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. He defined an element as a basic form of matter that cannot be broken down into simpler substances by chemical reactions. 

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

Characteristics of: 

Metals 

• They have a lustre (shine). 
• They have a silvery-grey 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 

• They display a variety of colours. 
• 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 

Some elements have intermediate properties between those of metals and nonmetals, they are called metalloids; examples are boron, silicon, germanium, etc. 

Compounds 

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

Elements react to form new compounds. The composition of each new substance is always fixed. The new substance has different properties. The constituents can be separated only by chemical or electrochemical reactions. 

Important Definitions in NCERT CBSE Class 9 Science Chapter 2 Notes ‘Is Matter Around Us Pure?’

Some important definitions covered in the  NCERT Class 9 Geography Chapter 2 notes are mentioned below:     

• Mixture: When two or more substances combine in any ratio, then the formed substance is called a mixture. 
• Solution: A homogenous mixture of two or more substances is called a solution. 
• Alloys: Alloys are mixtures of two or more metals or a metal and a non-metal 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. 
• Solvent: The component of the solution that dissolves the other component in it (usually the component present in a 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. 
• Saturated Solution: At a given temperature, when no more solute can be dissolved in a solution, then it is said to be a saturated solution. 
• Solubility: The amount of solute present in the solution at this temperature is called its solubility. 
• Suspension: A suspension is a heterogeneous mixture in which the solute particles do not dissolve but remain suspended throughout the bulk of the medium. 
• Colloidal Solution: A colloidal solution is a heterogeneous mixture of particles that are uniformly spread throughout the solution. 
• Element: An element is a basic form of matter that cannot be broken down into simpler substances by chemical reactions. 
• Compound: A compound is a substance composed of two or more elements, chemically combined with one another in a fixed proportion. 

Download the NCERT Class 9 Science Chapter 2 Notes PDF Here! 

Download Notes of all the Chapters of Class 9 Science: 

Chapter 1	Chapter 2	Chapter 3	Chapter 4	Chapter 5	Chapter 6
Chapter 7	Chapter 8	Chapter 9	Chapter 10	Chapter 11	Chapter 12

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