Is Matter Around Us Pure Class 9 Science — Revision Notes
This chapter distinguishes between pure substances and mixtures, and methods to separate mixtures. Students learn about elements, compounds, and identifica
TL;DR: This chapter distinguishes between pure substances and mixtures, and methods to separate mixtures. Students learn about elements, compounds, and ident…
Written & reviewed by the Syllab.in Academic Team (CBSE/NCERT subject experts) · Updated
This chapter distinguishes between pure substances and mixtures, and methods to separate mixtures. Students learn about elements, compounds, and identifica
Pure Substances
- Pure substance has constant composition and properties
- Element: pure substance made of one type of atom (e.g., oxygen, nitrogen)
- Compound: pure substance made of two or more elements chemically bonded
- Physical properties fixed for pure substances (melting point, boiling point)
Mixtures
- Mixture has variable composition
- Homogeneous mixture: uniform composition throughout (salt solution)
- Heterogeneous mixture: non-uniform composition (sand and sugar mix)
- Components retain individual properties in mixture
Separation Techniques
- Filtration: separate insoluble solid from liquid (filter paper)
- Evaporation: separate soluble solid from solution by heating
- Crystallization: obtain pure crystals of solid from solution
- Distillation: separate liquids based on boiling points
- Fractional distillation: separate multiple components with different boiling points
Chromatography
- Paper chromatography: separate colored dyes in solution
- Components move different distances based on solubility
- Used for food additives, ink analysis
- Rf value = distance traveled by component / distance traveled by solvent
Key Terms
- Element: Pure substance made of only one type of atom
- Compound: Pure substance made of two or more elements bonded together
- Mixture: Combination of two or more substances that retain individual properties
Frequently Asked Questions
How do you distinguish pure substance from mixture?
Pure substance has constant melting and boiling points. Mixture has range of melting and boiling points. Pure substance has fixed composition, mixture has variable composition.
Why is air a mixture and not a compound?
Air components (N2, O2, Ar, CO2) are not chemically bonded. They retain individual properties and can be separated physically. Therefore, air is a homogeneous mixture.
More Class 9 Science Revision Notes
- Matter in Our Surroundings
- Atoms and Molecules
- Structure of the Atom
- The Fundamental Unit of Life
- Tissues
- Motion
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