What is a pure substance?
Pure substances are defined as substances that are made up of only one type of atom or only one type of molecule (a group of atoms bonded together). The measure of whether a substance is pure is known as purity. For example, pure iron would only contain iron atoms, and, as in the sugar cube, pure sugar would only contain molecules of the substance called sucrose.
Pure substances exhibit very well-defined physical properties or properties that are not connected with the substance's ability to combine with different substances.