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A Chemical composition is the identity, and relative number, of the elements that make up any particular compound.

Composition of a substanceEdit

The chemical composition of a pure substance corresponds to the relative amounts of the elements that constitute the substance itself. It can be expressed by the empirical formula. For example the formula for water is H2O: this means that each molecule is constituted by 2 atoms of hydrogen (H) and 1 atom of oxygen (O) .

Composition of a mixtureEdit

The chemical composition of a mixture can be defined as the distribution of the single substances that constitute the mixture, called "components". In other words, it is defined giving the concentration of each component.

Because there are different ways to define the concentration of a component, as a consequence there are also different ways to define the composition of a mixture. For example it can be expressed as molar fraction, volume fraction, mass fraction, molality, molarity or normality.

Chemical composition of a mixture can be represented graphically in plots like ternary plot and quaternary plot.