Moles means avogadro number of molecules or atoms etc.,
Moles of a molecule = mass/ molar mass
Moles of a atom = mass/ atomic mass.
in Stoichometry moles is used at various places like
mass = moles * molar mass
Finidng moles is the first step in finding limiting reactant.
find the moles of 10 grams of Sodium hydroxide (NaOH)
moles = 10/40 [ Molar mass of NaOH = 40]
find the mass of 0.5 moles of calcium carbonate
moles = mass / molar mass
0.5 = mass/ 100 [ molar mass of Calcium carbonate = 100]
mass = 0.5 * 100
= 50 grams.
Finding moles is also used at different stages, depending upon the problem need