Substances can be divided into pure substances and mixed substances.
Pure substances can be further divided into elements and compounds.
Elements are made up of one kind of atom which cannot be broken into simpler substances
Compounds are made up of two or more kinds of atoms(elements), chemically combined in a fixed proportion.
Mixtures are made up of two or more kinds of atoms(elements) or compounds or both mechanically mixed in any proportion. Mixtures are of two kinds : homogeneous mixtures and heterogeneous mixtures.
In homogenous mixture composition is uniform and properties are same throughout the mixture.
In Heterogeneous Mixture the composition is non-uniform throughout and properties vary throughout the mixture.
Purification of substances:
Sedimentation :The process of deposition of a solid material from a state of suspension or solution in a fluid. e.g. obtaining clear water from muddy water.Â
Decantation : Decantation is a process for the separation of mixtures, by removing a top layer of liquid from which a precipitate has settled.
Filtration: Filtration is the process of removing one substance or material from another by mechanical means. e.g. tea is filtered using a strainer.
Evaporation: Soluble solid constituent is separated from its liquid constituent. Solid component remains behind in evaporating dish, liquid component is lost.
Distillation: Soluble solid constituent from its liquid constituent. Solid component remains behind in distillation flask and liquid component is collected after condensation
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