Final answer:
A pure substance has a consistent density when measured under constant conditions because density is an intensive property that remains the same regardless of the amount of substance. This property facilitates the precise identification of substances.
Step-by-step explanation:
A pure substance always has consistent density when measured under constant conditions. This is because density is an intensive property of matter, meaning it does not depend on the amount of substance present. It is defined as the mass of an object divided by its volume, and for pure substances, this ratio remains constant regardless of sample size.
For example, the density of pure water at 25° C is 0.998 g/cm³, and the density of a pure sample of tungsten is always 19.25 g/cm³. These values showcase the precision with which the densities of substances can be reported. Precision refers to how closely a measurement matches the same measurement when repeated, and for a pure substance in controlled conditions, the density is a highly precise measurement.
Substances exhibit this uniform density because they are homogeneous, meaning they have a constant composition throughout. This characteristic allows us to use density as a property to distinguish one substance from another. When conditions such as temperature and pressure are kept the same, the density of a pure substance remains consistent and can be used to identify it.