A pure substance is a homogeneous form of matter which has a definite or constant composition and distinct properties. Every bit appears the same. Today we can detect one in a trillion parts of impurity of some substances. A pure substance can be identified by appearance, smell, and other properties. All specimens of the same pure substance have identical composition, color, chemical and physical properties including a constant melting point and a constant boiling point.
Mixtures vary in composition.
This is accomplished by techniques such as filtration, sublimation, distillation, fractional crystallization, and all kinds of chromatography. Elements Substances that cannot be decomposed into simpler materials by chemical reactions. Compounds Substances formed from two or more elements in which the elements are always chemically combined in the same fixed proportions by mass. A physical property can be measured or observed without changing the composition or identity of the sustance. They are characteristics which are detected by our senses or instruments which are extensions of our senses.