It is specified as the quantity of any substance constituting the equivalent amount of fundamental units as the identical number of fundamental units in pure sample of 12C measuring accurately 12 g. Mole in Latin specifies pile, heap or collection. The amount of entities constituting one mole was experimentally found to be 6.022 X 1023, which is a constant and it is termed as an Avogadro’s constant (NA) or Avogadro’s number. This constant always represented in terms of per mole. With Avogadro’s number, researchers can compare and discuss about very large numerical, which is useful since substances in our everyday life are composed of large number of molecules and atoms. Avogadro’s number is essential to understand both the formation of molecules along with their combinations and interactions. For instance, since one oxygen atom will merge with two nitrogen atoms to form a nitrous oxide molecule (N2O), a mole of oxygen (O) (6.022 X 1023 of O atoms) will incorporate with 2 moles of N atoms (2 × 6.022×1023 of N atoms) to form a mole of N2O.
Gram atomic mass of a substance is defined as the quantity of substance in grams whose numerical value is identical with the atomic mass of that matter. Gram atomic mass seems to be nothing but the mass of an unit mole of an element. It can be measured by using an atomic weight of that element from the periodic table as well as expressing it in grams. So, for example, iron (Fe) has 55.845 u of atomic weight, and so its gram atomic mass is 55.845 g. Therefore, each mole of iron atoms has 55.845 g of mass.
We need to find out the molecular formula to calculate the gram molecular mass. We have to determine the comparable atomic masses of all the constituents in the molecular formula, at first. Then, we have to multiply the subscript after the symbol of every element which represents the quantity of atoms by their atomic masses. If subscript is not there, then there must be sole atom of an element is present in the molecule. Finally, we need to add all the values to get the required gram molecular mass. For example, gram molecular mass of nitrogen is 28 g instead of 28 u.