Mole Concept
A mole (Mole or Mol) is a number that is equal to the number of atoms present in 12 grams of carbon-12. With the help of modern techniques, the number of atoms present in 12 grams of carbon-12 has been determined. Its value has been found to be 6.0220943 x 10²³. Generally this value is used up to three decimal places only. Therefore
1 mole = 6.022 x 10²³
This number is known as Avogadro's number. Its value was not determined by Avogadro, but it is named Avogadro's number to reflect the importance of Avogadro's contribution to chemistry.
It would be useful to make it clear here that just as dozen is a number, mole is also a number.
- 1 dozen Alpins = 12 Alpins
- 1 mole Alpins = 6.022 × 10²³ Alpins
- 1 dozen hydrogen atoms = 12 atoms of hydrogen
- 1 mole hydrogen atom = 6.022×10²³ atoms of hydrogen
- 1 mole hydrogen (H2) = 6.022×10²³ molecules of hydrogen
- 1 mole ammonia (NH3) = 6.022×10²³ molecules of ammonia
- 1 mole Cl- = 6.022×10²³ anions of chlorine
- 1 mole electron = 6.022 × 10²³ electrons
It is clear that mole (mole or mol) is not a short form of molecule and this number can be used for any type of particle (atom, molecule, radical, ion, electron, proton, neutron etc.).
According to the above description, for any type of particle
Number of moles = Number of particles / 6.022× 10²³ ...(1)
Mass of a Mole
According to the definition of a mole, 1 mole of carbon-12 weighs 12 grams, which is equal to its gram-atomic weight. On this basis it can be shown that the weight of 1 mole of atoms of an element is equal to its gram-atomic weight. 1 mole of atoms is also known as 1 gram-atom. Similarly, the weight of 1 mole of molecules of an element or compound is equal to its gram-molecular weight. 1 mole of molecules is also called 1 gram-molecule. Therefore
For atoms -
weight of 1 mole (1 gram-atom) = gram-atomic weight
∴ Number of moles = Atomic mass / Weight in grams ...(2)
For molecules
Weight of 1 mole (1 gram-molecule) = gram-molecular weight
∴ Number of moles = Weight in grams / Molecular weight ...(3)
For ions -
Weight of 1 mole (1 Gram-ion) = Gram-ion Weight
∴ Number of moles = Weight in grams / Weight of ion ...(4)
On combining the above formula no. (2), (3) and (4) for any type of particles
Number of moles = Weight in grams / Molar mass ...(5)
The mass in grams of 1 mole of a substance is called molar mass. It is clear that for atoms it is equal to atomic mass, for molecules it is equal to molecular mass and for ions it is equal to ionic mass.
According to the definition of atomic weight, it is the ratio of two weights and it does not have any unit. Similarly, there is no unit of atomic Weight, ion Weight and molar mass. While using the above formula no. (2), (3), (4) and (5) generally no unit is used for any term included in it. Some authors while using the above formula no. (2), (3), (4) and (5) The unit of number of moles is mole, the unit of quantity in gram is gram and the unit of atomic Weight, molecular Weight, ion Weight and molar mass is gram/mole. On this basis, the units of atomic Weight, molecular Weight, ion Weight and molar Weight are also considered gram/mol.
On combining the above formula no. (1) and (5)-
Amount in grams = Number of particles / Avogadro's number × Molar mass ...(6)
With the help of the above formula, the number of particles can be easily determined from the quantity in grams and the quantity in grams from the number of particles.
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