Mole Concept

What is the Mole Concept?

Most of our routine items are sold in specific numerical quantities along with definite names. For instance, soda cans come in a pack of six, bananas are sold by means of dozen (12), pens often come in a gross (144 or 12 dozen), papers are packed in reams (500, and not 400 or 600), seems to be a large number. We know that the magnitude of an atom is very small and it cannot be countable. The uniqueness of each and every substance is not only defined by the different kinds of ions or atoms present in it, also it depends on the number of ions or atoms present in that substance. For instance, nitrous oxide N2O, and nitrogen dioxide NO2, are identical in that their particular molecule consists of oxygen and nitrogen atoms. However, due to their difference in the number of oxygen and nitrogen atoms, those substances exhibit different properties, which require the establishment of new unit for the measurement of quantity of substance and any readily quantifiable mass of a compound or an element contains an exceptionally large quantity of atoms, ions, or molecules, which requires an immense numerical unit to count. For this purpose, the mole is used, which seems to be very important for modern chemistry.

What is a Mole?


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.

What is Molar mass?

A mole is an entity which helps us to match the particles of given substance along with its mass. The molecular weight or molar mass is nothing but the summation of masses of each and every atom in grams which constitute a mole of a molecule. Molar mass can be determined by dividing the given mass of any substance by the quantity of that substance in g/mol. For instance, atomic mass of copper is 63.546 amu or 63.546 g/mol. In this 63.546 g of copper, there is a mole, or 6.022 X 1023 copper atoms.

An important feature is that each element's molar mass is just its atomic mass measured in g/mol. Though, it can also be computed by finding the product of atomic mass given in amu and the constant of molar mass (1 g/mol). For instance, molar mass of a molecule CaCl2 can be found out by combining the atomic masses of both calcium (40.078 g/mol) and that of chlorine (2 X 35.45 g/mol) and doing so we will get the molar mass as 110.98 g/mol.

Gram Atomic Mass and Gram Molecular Mass


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. 

Number of gram atoms = mass of the element (g) /Atomic mass of the element (g)

Gram molecular mass of any substance is expressed as the quantity of substance in grams whose numerical value is identical with the molecular mass of that substance. Gram molecular mass can be stated as the mass of a unit mole of the molecular substance in grams. It is same as the molar mass. The one and only difference is that the gram molecular mass indicates the mass unit has to be utilized. It may be notified in grams per mole or in grams (g).

To find the Gram Molecular 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.

Number of gram molecules = mass of the substance (g) / molecular mass of the substance (g)

Gram Molecular Volume:

It is defined as the volume bound up by a mole of each gas under standard conditions of temperature (273 K) and pressure (1 atm) (at STP). Its value was found to be 22.4 liters for all the gases. It is also called as molar volume and it is represented as Vm.

1 mole of a gas = 1 Gram Molecular Mass
                           = 22.4 L (STP)
                          = 6.022 X 1023 molecules.

Molar volume of any substance can be expressed by means of dividing molar mass by its density.
Molar Volume = Molar mass/ density
The SI unit of molar volume is m3 /mol, practically it is cm3 /mol for solids and liquids and dm3/mol for the gases.