A mole is defined as the amount (mass) of a substance that contains 6.02 x 1023 number of particles ( atoms, molecules or formula units). It establishes a link between mass of a substance and number of particles as shown in summary of molar calculations. It is abriviated as ‘ mole’ .
You know that a substance may be an element or compound ( molecular or ionic). Mass of the substance is eather one of the following: atomic mass, molecular mass or formula mass. These masses are expressed in atomic mass unit (amu). But when these masses are expressed in grams, they are called as molar masses.
Scientists have agreed that Avogadro’s number of particles are present in one molar mass of a substance. Thus, quantitative definition of mole is the atomic mass, molecular mass or formula mass of a substance expressed in grams is called mole.
Atomic mass of carbon expressed as 12g = 1 mole of carbon
Molecular mass of H2O expressed as 18g = 1 mole of water
Molecular mass of H2SO4 expressed as 98g = 1 mole of H2SO4
Formula mass of NaCl expressed as 58.5 g = 1 mole of NaCl
Thus, the relation between mole and mass can be expressed as:
A detailed relationship between a substance and a mole through molar mass and number of particles is present here.
Summary showing a relationship between a substance and a mole.
Example for calculation of Moles:
Calculate the gram molecule (number of moles) in 40 g of H3PO4.
Given mass of H3PO4 = 40 g
Molecular mass of H3PO4 = 98 gmol-1
Putting these values in equation
Therefore, 40 grams will contain 0.408 gram molecule (mol) of H3PO4 .