Question

What is meant by pure substance?

Answer 1

Hint: To answer this question you must know what a pure substance is. A pure substance is a substance which has only one type of atoms or molecules thereby having a constant composition and structure.

Complete answer:
Substances which are made up of only one kind of atoms or molecules and have a definite composition throughout and have a fixed structure are known as pure substances. For instance a certain compound contains elements in a fixed proportion by mass always.
Elements and compounds are pure substances. Elements are substances composed of only one type of atom. Copper metal, silver metal, oxygen gas, etc. are all elements. While compounds are substances formed by the combination of two or more elements in a definite ratio. Water is a compound as it is formed by the combination of hydrogen and oxygen (elements) in a fixed ratio. It has a constant composition throughout.

Note:
A substance can be either an element, a compound or a mixture. Elements and compounds have a constant composition throughout and can thus be said as pure substances.
On the other hand, mixtures have different characteristics than a pure substance. They are known as impure substances. Mixtures are composed of different elements or compounds mixed together, or more than one pure substance combined together in any proportion. The components in a mixture do not have any definite ratio and thus no definite composition. Their components can be separated easily using physical means like evaporation, filtration, etc.