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

1. Elements: Elements are the simplest form of pure substances, consisting of only one type of atom. They cannot be further broken down into simpler substances by physical or chemical methods. Examples of elements include hydrogen, oxygen, carbon, and iron. Elements can exist in different states of matter: solid, liquid, or gas, depending on factors such as temperature and pressure. They are further categorized into metals, non-metals, and metalloids based on their properties.
2. Compounds: Compounds are pure substances composed of two or more different types of atoms chemically combined in fixed proportions. Unlike elements, compounds can be broken down into simpler substances (elements or other compounds) by chemical reactions. Compounds have properties distinct from those of their constituent elements. Examples of compounds include water (H2O), sodium chloride (NaCl), carbon dioxide (CO2), and glucose (C6H12O6).

Metals

Non-Metals

Metalloids

Illustration – 1:

Copper:

1. Ductility and Malleability: Copper can be easily shaped into wires and thin sheets.
2. Conductivity: Copper conducts heat and electricity efficiently.

Sulphur:

1. Brittleness: Sulphur is not malleable or ductile and fractures into fragments when hammered.
2. Poor Conductivity: Sulphur does not conduct heat or electricity effectively.

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.

Tyndall effect: Scattering of light by colloidal particles

Classification of Colloids

1. Sol: In this type, solid particles are dispersed within a liquid medium. An example is a paint.
2. Solid sol: Here, solid particles are dispersed within another solid medium. One example is alloys, like brass.
3. Aerosol: Aerosols consist of solid or liquid particles dispersed within a gas. Examples include smoke and mist.
4. Emulsion: In an emulsion, small droplets of one liquid are dispersed within another immiscible liquid. Mayonnaise and milk are classic examples.
5. Foam: Foam is created when gas bubbles are dispersed within a liquid or solid medium. Examples include whipped cream and foam insulation.
6. Solid foam: In solid foam, gas bubbles are dispersed within a solid medium. Styrofoam and pumice are examples.
7. Gel: Gels have a solid-like consistency but are actually composed of a liquid dispersed within a solid. Examples include gelatin and agar.

Separation of mixture

Sublimation: Used for substances that undergo sublimation, where they transition directly from solid to vapor without passing through the liquid phase. For example, separating ammonium chloride and common salt.

Filtration: Effective for separating solids from liquids or suspensions. It involves passing the mixture through a filter medium, which traps the solid particles while allowing the liquid to pass through.

Centrifugation: Utilized to separate suspended particles from a liquid by spinning the mixture at high speeds in a centrifuge. Denser particles settle at the bottom, forming a pellet, while the liquid remains above.

Evaporation: Involves heating a liquid mixture to evaporate the solvent, leaving behind the solute in solid form. This method is commonly used to recover dissolved solids from a solution.

Crystallization: By allowing a supersaturated solution to cool or evaporate slowly, crystals of the solute form and can be separated from the solution.

Chromatography: Separates components based on differences in their affinity for a stationary phase and a mobile phase. This method is often used in chemical analysis and purification processes.

Distillation: Separates components of a mixture based on differences in their boiling points. The mixture is heated to vaporize the more volatile component, which is then condensed and collected.

Fractional Distillation: Similar to distillation but used for mixtures with closer boiling points. A fractionating column is employed to achieve better separation.

Separating Funnel: Used to separate immiscible liquids by allowing them to settle into distinct layers based on their densities, which can then be drained separately.