• Pure substance consists of a single type of substance . • Mixture consists of two or more pure substances.
• Pure substance cannot be separated into other substances by physical methods • Mixture can be separated into its components by physical methods.
• Pure substance has its own definite properties • Mixture shows the properties of its components.


Elements are made up of one kind of atoms only. Compounds are made up of one kind of molecules only.

2. Types of Mixtures Mixtures can also be grouped

i) On the basis of their physical states:






• Salt and sugar • Salt and water • Dust in air
LIQUID • Mercury and copper • Alcohol and water • Clouds
GAS • Hydrogen and palladium • Oxygen and water • Air

ii) On the basis of miscibility:

Homogeneous Mixture

Heterogeneous Mixture

• It consists of single phase.
• Uniform composition.
• Example: Sugar dissolved in water
• It consists of two or more phase.
• Does not have uniform composition.
• Example: Air, sand and common salt.

Types of Solutions

a) on the basis of size of solute particles:

True solution

Sol [ Colloid]


• Homogeneous • Heterogeneous • Heterogeneous
• Size of solute particles is less than 1 n m or 10-9 m . • Size of solute particles is between 1 nm to 1000 nm. • Size of solute particles is more than 1000 nm.
• Particles cannot pass through filter paper • Particles can pass through filter paper. • Particles cannot pass thorough filter paper.
• Stable • Stable and settle only on centrifugation • Unstable and settle down on its own.
• Solution of sodium chloride in water, sugar & water. • Milk , Fog • muddy water, chalk & water,
• smoke in the air.
Physical changes

Changes that do not result in the production of a new substance.

• If you melt a block of ice, you still have H2O at the end of the change.
• If you break a bottle, you still have glass

Examples : melting, freezing, condensing, breaking, crushing, cutting, and bending.

Chemical changes

- Changes that result in the production of another substance.

• As in the case of autumn leaves, a change in color is a clue to indicate a chemical change.

• a half eaten apple that turns brown.

Important Questions (Prev Lesson)
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