8.1.1 Pure Substances

A pure substance refers to a substance that consists of only one type of element or compound. It is not mixed or contaminated with any other substances. Pure substances have distinct physical and chemical properties that differentiate them from mixtures.

Pure elements are composed of atoms of the same type. Examples of pure elements include gold (Au), oxygen (O₂), and carbon (C). Pure compounds, on the other hand, are composed of molecules or ions with definite chemical formulas. Examples of pure compounds include water (H₂O), sodium chloride (NaCl), and glucose (C₆H₁₂O₆).

One characteristic of pure substances is their specific melting and boiling points. These are the temperatures at which a substance transitions from a solid to a liquid (melting) or from a liquid to a gas (boiling) under normal atmospheric pressure. Melting and boiling point data are valuable in distinguishing pure substances from mixtures. A pure substance will exhibit a sharp and consistent melting or boiling point, whereas mixtures show a range of melting and boiling temperatures as the various components within the mixture separate at different temperatures.

It is important to note that the term "pure substance" can also be used in everyday language to describe a substance that has not been mixed or adulterated with any other substances. For example, pure milk refers to milk that is unadulterated, without any additives or contaminants.