Why are compounds considered pure substances, while mixtures are … - Vidyadip

Question

Why are compounds considered pure substances, while mixtures are not?

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Answer

Compounds are pure substances because they are made up of only one type of molecule and have a uniform and definite composition throughout. For example, every molecule of water (H₂O) is identical, consisting of two hydrogen atoms and one oxygen atom chemically bonded together. This fixed composition results in consistent physical and chemical properties, like a specific boiling point and density.
Mixtures are not pure substances because they consist of two or more substances that are physically blended, not chemically bonded. The components of a mixture retain their individual properties and can be present in varying proportions. For example, air is a mixture of nitrogen, oxygen, and other gases, and the amount of each gas can vary.

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