Classify each as a pure substance or a mixture.
Pure substances are made of only one kind of substance and will have a definite and constant composition.
Pure substances can be classified into elements and compounds
An element is the simplest form of a pure substance. It can be defined as a pure substance which can neither be decomposed into, nor built from simpler substances by ordinary physical or chemical methods eg. Iron, oxygen, calcium etc.
A compound may be defined as a substance which is obtained by the union of two or more elements in definite proportion by weight and into which it may be decomposed by suitable chemical methods.eg carbon dioxide, water, common salt etc.
A mixture may be defined as a combination of two or more elements or compounds in any proportion so that the components do not lose their identity.