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

Is Matter Around Us Pure Notes are designed to provide a comprehensive, step-by-step breakdown of CBSE Class 9 Science Chapter 2. It is based on the NCERT curriculum and is helpful for students preparing for Class 9 exams. 

Is Matter Around Us Pure Notes PDF is given here for students who want clear, well-structured revision material for Class 9 Science. Is Matter Around Us Pure Class 9th Notes cover all important topics including pure substances, mixtures, solutions, suspensions, colloids, and different methods of separation.

Class 9 Is Matter Around Us Pure Notes

Is Matter Around Us Pure Class 9th Notes cover every concept of the Chapter 2. It helps students understand the basics like ‘What is Matter’ and related concepts. 

What is Matter?

In scientific terms, Matter is anything that has mass and occupies space (volume). While we learned about the physical states (solid, liquid, gas) in Chapter 1, this chapter focuses on the Chemical Classification of matter.

Chemical classification divides matter into two broad categories:

1. Pure Substances: Made up of only one type of particle (atoms or molecules).

2. Impure Substances (Mixtures): Made up of two or more different types of particles mixed together physically.

What are Pure Substances?

A pure substance has a fixed chemical composition and distinct properties. It cannot be separated into simpler components by physical methods like filtration. Pure substances are further divided into elements and compounds.

A. Elements

An element is the simplest form of matter that cannot be broken down further by chemical reactions.

• Metals: Shiny (lustrous), malleable (can be beaten into sheets), ductile (can be drawn into wires), and sonorous. (e.g., Iron, Gold).

• Non-metals: Dull, brittle, and poor conductors of heat and electricity. (e.g., Oxygen, Sulphur).

• Metalloids: Elements that show intermediate properties (e.g., Boron, Silicon).

B. Compounds

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

• Crucial Point: The properties of a compound are entirely different from its constituent elements. For example, Hydrogen (combustible gas) and Oxygen (supports combustion) combine to form Water (H2​O), which is a liquid used to extinguish fire.

What are Mixtures? 

When two or more substances mix together without a chemical reaction, it is a Mixture. There are two types of mixtures, i.e., homogeneous and heterogeneous. Below are the definitions for both: 

• Homogeneous Mixtures: These mixtures have a uniform composition throughout. You cannot see the boundaries between components (e.g., salt in water, alloys like brass).

• Heterogeneous Mixtures: These mixtures have a non-uniform composition and visible boundaries (e.g., oil and water, sand and salt).

Is Matter Around Us Pure Notes PDF Download​

Is Matter Around Us Pure Notes PDF Download section provides students with complete, well-organised notes based strictly on the NCERT syllabus. The notes explain important concepts such as pure substances, mixtures, solutions, colloids, and separation methods in a clear and simple manner. 

The PDF format is useful for last-minute preparation before exams. Students can download the notes, revise important definitions and differences, and use them as a reliable reference for school tests and CBSE examinations. 

Is Matter Around Us Pure Notes PDF Download​

Solutions, Suspensions and Colloids

The matter around us is incredibly diverse, ranging from simple substances to complex mixtures. Understanding the distinctions between these forms of matter is essential for comprehending their behavior and properties.

• Solutions: One of the most common forms of matter is solutions, which are homogeneous mixtures composed of a solute dissolved in a solvent. Solutions can vary in their composition, with some being saturated (containing the maximum amount of solute at a given temperature) and others being unsaturated (able to dissolve more solute). Solubility, or the ability of a solute to dissolve in a solvent, depends on factors such as temperature.

• Suspensions: On the other hand, suspensions are heterogeneous mixtures where solid particles are dispersed throughout a liquid without dissolving. Unlike solutions, suspension particles are larger and can be observed with the naked eye or under a microscope. Suspensions are typically unstable and settle over time, forming a precipitate.

• Colloids: Colloids are intermediate between solutions and suspensions, with particles that are larger than those in solutions but smaller than those in suspensions. These particles are evenly dispersed throughout the mixture, giving colloids a homogeneous appearance. Colloidal particles exhibit Brownian motion, a zigzag movement first observed by Robert Brown in 1828.

Understanding the properties and characteristics of solutions, suspensions, and colloids provides valuable insights into the behavior of different types of matter in our surroundings.

What is the Tyndall Effect?

The Tyndall effect is a fascinating phenomenon observed when light passes through a colloidal solution. Colloidal particles, being larger than the molecules in true solutions, have the ability to scatter light. 

When a beam of light is directed through a colloidal solution in a darkened environment, the path of the light becomes illuminated and visible when viewed from the side. This occurs because the colloidal particles scatter the light in all directions, making the path of the beam visible. 

It's akin to seeing a beam of light in a dusty room, where the particles in the air scatter the light and make it visible. This scattered light entering our eyes allows us to perceive the path of the beam, showcasing the fascinating interplay between light and matter at the microscopic level.

What is Concentration of a Solution?

Concentration tells us exactly how much solute is dissolved in a solvent. If you have two cups of tea, one with a teaspoon of sugar and one with five, the second one is more "concentrated."

Saturated vs. Unsaturated Solutions

• Unsaturated Solution: If you can add more solute (like salt) to a liquid and it still dissolves, the solution is unsaturated.

• 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. If you add more salt, it will simply sit at the bottom.

• Solubility: This is the maximum amount of a solute which can be dissolved in 100 grams of a solvent at a specific temperature.

• Note: Solubility increases with temperature. This is why you can dissolve more sugar in hot milk than in cold milk.

How can we Calculate Concentration?

In Class 9, you will mostly use these two formulas to solve problems:

1. Mass by Mass Percentage: Used when both solute and solvent are given in grams.
   Concentration=(Mass of SolutionMass of Solute​)×100
   (Remember: Mass of Solution = Mass of Solute + Mass of Solvent)

2. Mass by Volume Percentage: Used when a solid solute is dissolved in a liquid.
   Concentration=(Volume of SolutionMass of Solute​)×100

How Physical vs. Are Chemical Changes Different?

Physical Change are changes that affect the physical properties (size, shape, state) but not the chemical identity. They are mostly reversible. If you melt ice, you get water; if you freeze it, you get ice again. Example: Breaking a glass, boiling water, mixing sand and water.

Chemical Change (Chemical Reaction): These occur when substances react to form entirely new products with different properties. They are usually very hard to reverse. Example: Burning a candle (the wax turns into CO2​ and water vapor), rusting of an iron nail, cooking an egg.

Separation Techniques and How to Purify Matter

In nature, substances are rarely pure. We use different physical properties to separate them.

1. Evaporation: It is used to separate a non-volatile solute from a volatile solvent. By heating the mixture, the liquid component (solvent) turns into vapor and escapes into the air, leaving behind the solid component (solute) as a residue in the evaporating dish.

2. Centrifugation: Centrifugation is a method used to separate fine suspended particles from a liquid by spinning the mixture at very high speeds. The principle is that the denser particles are forced to the bottom while the lighter particles stay at the top. It is commonly used in dairies to separate cream from milk.

3. Separating Funnel: This technique is used to separate two immiscible liquids (liquids that do not mix). The mixture is poured into the funnel and allowed to stand until it forms two distinct layers based on density. The heavier liquid forms the bottom layer and is drained out by opening the stopcock, leaving the lighter liquid inside. Below is the diagram given for reference: 

4. Sublimation: Sublimation is used to separate a mixture containing a component that changes directly from a solid to a gas upon heating (sublimable) from a non-sublimable impurity.

The mixture (e.g., Ammonium Chloride and Salt) is placed in a china dish with an inverted glass funnel over it. The end of the funnel is plugged with cotton. When heated, the Ammonium Chloride turns into vapors, rises, and hits the cool inner walls of the funnel, where it turns back into a solid (called the sublimate). The salt stays in the dish.

5. Chromatography: It is a technique used to separate different solutes that dissolve in the same solvent but have different solubilities. In the given diagram, a drop of ink is placed on a strip of filter paper, which is then dipped into a jar of water (the water level must be below the ink spot). As the water moves up the paper by capillary action, it carries the dyes with it. The dye that is more soluble in water moves faster and higher, while the less soluble dye stays lower, creating a pattern of colored spots.

6. Distillation: It is used to separate miscible liquids that have a large difference in their boiling points (more than 25°C). The mixture is heated until the liquid with the lower boiling point evaporates, passes through a condenser where it cools back into a liquid, and is collected in a separate flask.

7. Fractional Distillation: This method is used when the boiling point difference between miscible liquids is less than 25°C. It uses a fractionating column filled with glass beads. 

In the given diagram, this looks like simple distillation but adds a fractionating column filled with glass beads. As the vapors of both liquids rise, the beads provide a large surface area for them to cool and condense. The liquid with the higher boiling point condenses and falls back down, while the liquid with the lower boiling point stays as vapor, reaches the top, and passes into the condenser to be collected.

8. Crystallization: It is the process of obtaining a pure solid from its saturated solution in the form of crystals. It is considered better than evaporation because it prevents the decomposition of solids (like sugar) that might happen during high-heat evaporation and ensures that impurities remaining in the solvent do not mix with the final product.