As you see, the concept of chemical substance - or simply substance, as we will call it from now on - is closely related to the study of chemistry.
Chemists consider that A substance is a portion of matter that has well-defined properties that are characteristic of it.. Just as you can recognize a friend for a set of characteristics (skin color, voice tone, nose shape, walk, speech, hair color and texture, size, etc.), chemists identify substances by their full properties.
Among these properties are the fusion point, O boiling point, a density, the fact that flammable or not, a color, O odor etc.
Two different substances may eventually have one or two equal properties, but never all of them. If it happens that all properties of two substances are equal, then they are actually the same substance.
A sample of water, whatever its origin (rain, river, sea, lake, glacier, laboratory produced etc.), always has the same properties.
So any colorless liquid with MP = 0 ° C, PE = 100 ° C and d = 1.0 g / cm3It is classified as water. And so on.
When a substance is produced in the laboratory or extracted from some natural source, and is suspected to be a new substance, chemists first determine its properties.
If they totally coincide with those of a known substance, then it will not be a new substance. If, on the other hand, there is no known substance with these properties, then a new substance has indeed been discovered.