CBSE
CLASS 9 SCIENCE
CHAPTER 2
IS MATTER AROUND US PURE
NOTES
1.Matter: Matter is anything that occupies space and has mass. It can be classified into two types: pure substances and mixtures.
2.Pure Substances: Pure substances are made up of only one type of particle and have a fixed composition throughout. They can be further classified into elements and compounds.
a.Elements: Elements are pure substances that cannot be broken down into simpler substances by any chemical means. They consist of only one type of atom. For example, oxygen, hydrogen, carbon, etc.
b.Compounds: Compounds are pure substances composed of two or more elements chemically combined in fixed proportions. They can be broken down into simpler substances by chemical reactions. For example, water (H2O), sodium chloride (NaCl), carbon dioxide (CO2), etc.
3.Mixtures: Mixtures are composed of two or more pure substances physically mixed together. The components of a mixture can be separated by physical means such as filtration, evaporation, etc. Mixtures can be classified into homogeneous and heterogeneous mixtures.
a.Homogeneous Mixtures: Homogeneous mixtures have a uniform composition throughout, and the individual components are not visible. For example, saltwater, air, sugar dissolved in water, etc.
b.Heterogeneous Mixtures: Heterogeneous mixtures have a non-uniform composition, and the individual components can be seen. For example, a mixture of sand and iron filings, oil and water, etc.
4.Solutions: Solutions are homogeneous mixtures where one substance (solute) is dissolved in another substance (solvent). The solute particles are evenly distributed at the molecular level. For example, sugar dissolved in water, salt dissolved in water, etc.
5.Suspensions: Suspensions are heterogeneous mixtures in which solid particles are dispersed in a liquid or gas but settle down over time. For example, muddy water, chalk-water mixture, etc.
6.Colloids: Colloids are heterogeneous mixtures in which the particles are larger than those in a solution but smaller than those in a suspension. The particles do not settle down and remain dispersed in the medium. For example, milk, fog, gelatin, etc.
7.Physical and Chemical Changes: Matter undergoes physical and chemical changes.
a. Physical Changes: Physical changes are reversible changes in which the composition of the substance remains the same. For example, melting, boiling, cutting, etc.
a. Chemical Changes: Chemical changes are irreversible changes in which new substances with different properties are formed. For example, burning, rusting, digestion, etc.
8.Separation Techniques: Various separation techniques are used to separate the components of a mixture based on their physical properties.
a. Filtration: Used to separate insoluble solids from liquids using a porous barrier (filter paper).
b. Evaporation: Used to separate a soluble solid from a liquid by heating and evaporating the liquid, leaving behind the solid.
c. Distillation: Used to separate a mixture of liquids with different boiling points by heating and condensing the vapors.
d. Chromatography: Used to separate components of a mixture based on their different affinities for a mobile phase and a stationary phase.
☆ These are some key points to understand Chapter 2: Is Matter Around Us Pure in Class 9th Science. Make sure to refer to your textbook and class notes for a more detailed understanding and additional information.