Mixtures are composed of two or more pure substances, giving them a combination of distinct properties. Pure substances, on the other hand, possess a single, fixed set of properties. Both share common characteristics—such as weight, volume, color, and specific chemical behaviors—yet they diverge in key ways that are essential for chemistry and everyday applications.
Mixtures can be homogeneous or heterogeneous, and each component retains its own identity. Unlike pure substances, mixtures can be separated by physical means and their composition can vary widely. Despite this, mixtures inherit the fundamental properties of the pure substances that make them up.
Both mixtures and pure substances exhibit measurable physical attributes: weight, volume, and color. Solids also show shape, hardness, and texture. They each have characteristic boiling and solidification points; mixtures may display multiple such points corresponding to the constituent substances.
Special cases arise when a homogeneous or heterogeneous mixture consists of a single pure compound in two states—e.g., a mixture of ice and liquid water. Although the components differ physically, the chemical identity remains the same, qualifying the system as a pure substance.
In terms of chemical behavior, mixtures and pure substances share properties like flammability, toxicity, heat of combustion, and reactivity. Homogeneous mixtures show uniform chemical characteristics throughout, while heterogeneous mixtures can vary from one region to another.
Pure substances are chemically uniform; their composition is fixed, whether they are an element or a compound. The proportion of each element or atom remains constant across all samples.
Mixtures lack this fixed composition. Whether they are homogeneous solutions such as saltwater or heterogeneous blends like oil and vinegar, the relative amounts of each component can change freely. This flexibility is a defining feature of mixtures.
Moreover, mixtures can be decomposed into their constituent pure substances using purely physical techniques: distillation (separating liquids or a liquid from a solid), filtration (removing solids from liquids), centrifugation (differentiating by density), and decanting (separating a liquid from a heavy solid). Pure substances cannot be broken down into simpler materials through such means.
