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CBSE | Class 9 | science
Read the chapter in a clean notebook-style flow before moving into deeper practice.
Summary Note
Key concept recap
In everyday language, substances like milk or juice may be called 'pure,' but scientifically, most are mixtures.
A pure substance contains particles of only one kind and shows uniform properties throughout.
Mixtures contain more than one type of substance, combined physically, not chemically.
Summary Note
Key concept recap
Mixtures are classified into homogeneous and heterogeneous.
Homogeneous mixtures have uniform composition, like salt water.
Heterogeneous mixtures have visible components and non-uniform composition, like oil in water or sand in salt.
Summary Note
Key concept recap
A solution is a homogeneous mixture of two or more substances.
It contains a solute (the substance being dissolved) and a solvent (the medium in which solute dissolves).
Solutions can be solid, liquid, or gaseous. Examples include lemonade, air, and alloys.
Solutions are stable, the solute does not settle, and the path of light is not visible through them.
Summary Note
Key concept recap
Solutions can be dilute, concentrated, or saturated based on the amount of solute.
Saturation is reached when no more solute dissolves in a solvent at a given temperature.
Solubility is the maximum amount of solute that can dissolve in a given solvent at a given temperature.
Concentration is expressed in terms of mass percentage or volume percentage.
Summary Note
Key concept recap
A suspension is a heterogeneous mixture with visible particles dispersed in a liquid.
The particles scatter light (Tyndall effect), can be filtered, and settle when undisturbed.
Examples include chalk water and muddy water.
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Key concept recap
Colloids appear homogeneous but are actually heterogeneous.
They show Tyndall effect and are stable without particle settling.
Colloids have a dispersed phase and dispersion medium and cannot be filtered easily.
Examples include milk, fog, smoke, and foam.
Summary Note
Key concept recap
Physical changes do not alter the chemical nature of substances, like melting or boiling.
Chemical changes form new substances with different properties, such as rusting or burning.
Some changes involve both physical and chemical aspects, like burning a candle.
Summary Note
Key concept recap
Pure substances can be elements or compounds.
Elements consist of only one type of atom and cannot be broken down chemically. They can be metals, non-metals, or metalloids.
Compounds are formed by chemical combination of elements in a fixed ratio and have properties different from their constituents.
Examples: water (compound), iron (element), carbon dioxide (compound).
Summary Note
Key concept recap
Mixtures retain the properties of their constituents and can be separated by physical methods.
Compounds have fixed composition, unique properties, and can only be separated by chemical means.
This distinction is key to understanding how different materials behave in nature and industry.
Summary Note
Key concept recap
Mixture – Physical combination of two or more substances.
Homogeneous Mixture – Uniform composition throughout.
Heterogeneous Mixture – Non-uniform composition with visible components.
Solution – Homogeneous mixture of solute and solvent.
Suspension – Heterogeneous mixture with visible settling particles.
Colloid – Appears homogeneous but is a stable heterogeneous mixture showing Tyndall effect.
Solute – Substance dissolved in a solvent.
Solvent – Substance in which solute dissolves.
Saturation – Point at which no more solute dissolves in a solvent at given temperature.
Tyndall Effect – Scattering of light by colloidal particles.
Element – Pure substance of one type of atom.
Compound – Chemically combined substance with fixed ratio of elements.
