Question

define pure substance and mixture and give them at least one example

Answer 1

Matter can be broken down into two categories: pure substances and mixtures.Pure substances are further broken down into elements and compounds. Mixturesare physically combined structures that can be separated into their original components. A chemical substance is composed of one type of atom or molecule.

examples

pure substances pure sugar (sucrose), table salt (sodium chloride) and baking soda (sodium bicarbonate). Crystals, in general, are pure substances. 

Salt, sugar, and many other substances dissolve in water to form homogeneous mixtures.

Answer 2

A pure substance doesnot have to be a single chemical element or compound. A substance that has a fixed composition throughout is said to be a pure substance.

A mixture of various elements or compounds also qualifies as a pure substance as long as the mixture is homogenous.

For example, air, which is a mixture of various gases is often considered to be a pure substance. A mixture of gaseous air and liquid air is not considered as a pure substance since the composition of both would be different. This is due to different components in air condensing at different temperatures at a specified pressure.

A mixture of oil and water is not a pure substance since oil is immiscible in water.

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