The definite mass ratios involved in reactions suggested a convenient method for counting the number of atoms of each element participating in the re… - David W. Oxtoby

Investigating chemical reactions can be greatly complicated and often obscured by the presence of extraneous materials. So, the first step, therefore, is to learn how to analyze and classify materials to ensure that you are working with pure substances before initiating any reactions.

Laboratory or industrial chemical reactions are carried out with quantities that range from milligrams to tons, so we must be able to relate the relative atomic mass scale to the macroscopic scales used in practice. The link between the two scales is provided by Avogadro’s number (N_A).

The science of chemistry rests on two well-established principles: the conservation of matter and the conservation of energy.