Chemical composition is a concept of chemistry and it has a different meaning in pure substances and mixtures. The chemical composition of the pure substance refers to the proportion of each chemical element which is represented by the empirical formula. The empirical formula in physics also knows empirical equation which is derived from an experiment or guess out, rather than deduced from the "first-principles". It is a mathematical equation can predict observations. For example, water chemical formula is H2O, showing that the molecule consists of two hydrogen atoms (H) and an oxygen atom (O).

On the other hand, the chemical composition of the mixture is referring to the proportion of each pure substance in the material, and that is concentration of each portion. Since the concentration has many different representations, so the chemical composition of the mixture may be expressed in several different ways. Such as mole fraction, volume fraction, mass percent concentration, molality, molar concentration and molar equivalents concentration. Besides the volume fraction refer to assumed to be able to separated mixed gas and each gas at the same temperature and same pressure has a certain volume (which is the sum of the volume is mixed gas), the gas divided alone then to divide by the total volume of gas which is volume fraction.

The main chemical composition of molybdenum electrodes are molybdenum, international common molybdenum electrodes ingredients is 99.95%. And other content requirements are as follows: Al content cannot greater than 0.0020, Ca content cannot greater than 0.0030, Cr content cannot greater than 0.0050, Cu content cannot greater than 0.0010, Fe content cannot greater than 0.0060, Pb content cannot greater than 0.0020, Mg content cannot greater than 0.0010, Mn content cannot greater than 0.0010, Ni content cannot greater than 0.0030, Si content cannot greater than 0.0030, Sn content cannot greater than 0.0030, Ti content cannot greater than 0.0020. Other chemical ingredients can refer to the following table.