stoichiometric calculation

Mass of any atom can be expressed as the relative atomic mass in units of amu. Amu is the atomic mass unit which is 1/12 the mass of one carbon-12 atom. Thus, the mass of an atom in comparison to the carbon-12 atom is called relative atomic mass, amu or u is used as the unit. However, using mass of a single atom is not practical since atoms have so small masses. We rather use mass of a bunch of atoms which will be explained as mole.