Mole Concept and Molar mass


  • Unit of amount of substance.
  • One mole amount of substance that contains as many particles or entities  as there are atoms in exactly 12 g of the 12C isotope.

Molar mass:

  • Mass of one mole of a substance in gram
  • Molar mass in gram in numerically equal to atomic/molecular/formula mass in amu or u.

Mole concept

  • One mole of a substance (atoms, molecules, ions, or particles) is that quantity in number having a mass equal to its atomic or molecular mass in grams. 
  • The Avogadro constant is the number of particles (usually atoms or molecules) in one mole of a given substance.
  • Its value is equal to 6.022 ×1023 mol−1
  • The constant was named after the Italian scientist Amedeo Avogadro.
  • Avogadro number is denoted by N0.
  • One-mole molecule of any substance contains 6.022 x 1023 molecules.


Percentage composition:

Mass percentage of an element in a compound =  (Mass of that element in the compound / Molecular mass of the compound)×100 

Percentage yield:

  • It is the ratio of actual yield of the reaction to the theoretical yield multiplied by 100.
  • % yield = (Actual yield /Theoretical yield) ×100

Empirical and Molecular formula

  • An empirical formula represents the simplest whole number ratio of various atoms present in a compound.
  • The molecular formula shows the exact number of different types of atoms present in a molecule of a compound.

For example-

Hydrogen peroxide

  • Molecular formula – H2O2
  • Empirical formula – HO

For example –

Empirical formula of iron oxide , has 69.9% of iron and 30.1 % of oxygen by mass.

Empirical formula = Fe2O3