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NCERT Solution: Basic Concepts of Chemistry

MATTER

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MATTER

Anything which occupies space, possesses mass and can be felt is called matter.

CLASSIFICATION OF MATTER

ELEMENT

Pure substance consisting of one type of particles in the form of atoms eg. Cu, Na, Fe or molecules eg. H2, O2 etc.

COMPOUND

Pure substance consisting of molecules formed by the combination of atoms of different elements eg. CO2, H2O etc.

MIXTURES

Mixtures are substances made of two or more elements or compounds in any proportion. They may be homogeneous or heterogeneous.

SEPARATION OF MIXTURES

Mixtures can be separated into constituents by following methods:

Filtration can separate those mixtures whose one component is soluble in a particular solvent and other is not.
Distillation can be used to separate constituents of mixtures having different boiling points.
Extraction dissolves one out of several components of mixture.
Crystallisation is a process of separating solids having different solubilities in a particular solvent.
Sublimation separates volatile solids which sublime on heating from non-volatile solids.
Chromatography is the technique of separating constituents of a mixture which utilises the property of difference of adsorption on a particular adsorbent.
Gravity separation separates constituents having different densities.
Magnetic separation can separate magnetic components from non magnetic ones.

PHYSICAL AND CHEMICAL CHANGES

A change which does not affect chemical composition and molecular structure is a physical change and the one that involves alteration of chemical composition and molecular structure is a chemical change.

1. Chemical Combination is reaction between two or more elements or compounds to form a single substance.

2. Displacement means replacement of one element of compound by another.

3. Decomposition involves splitting of a compound to form two or more substances.

4. Combustion is a complete and fast oxidation of a substance.

5. Neutralisation is the reaction between acid and base to form a salt.

6. Polymerisation is the combination of molecules of same or different substances to form a single molecule called polymer

7. Photochemical changes occur in presence of visible or ultraviolet light.

8. Double decomposition or metathesis is the exchange of oppositely charged ion on mixing two salt solutions.

9. Hydrolysis involves reaction of salts with water to form acidic or basic solutions.