The mole, symbolized as mol, of a substance is the amount of physical quantity present in a molecule. It reduces the need of saying 6.02 x 10^23 (Avogadro's number) when describing atoms as the word "dozen" simplifies our request of 12 pastries. The mole is used in calculating the amount of molarity, or concentration, of a given substance and eases our understanding of the ideal gas law, titration, equilibrium and other chemistry principles.
To find the number of moles in a solution, start by multiplying the molarity (M) by the volume (V in liters) of the solution.
For example, if you have aluminum nitrate [AL(NO3)3] and want to determine the number of moles of nitrate (NO3) ions given that you have 3.00 L of a 0.340 M solution of aluminum nitrate, first calculate the number of mol in aluminum nitrate = M*V = (.340)(3.00) = 1.02 moles of aluminum nitrate.
Determine the number of ions of your molecule of interest that are present in the substance.
With the aluminum nitrate example, there are 3 (NO3) ions present in the compound.
Multiply the number of ions of your molecule of interest to the total number of moles of the substance.
Again, with the example, we would do 3*1.02 moles = 3.06 moles of (NO3). In other words, there are 3.06 moles of nitrate in the solution.