⁕ What is mole?
↪ It is not possible to count the number of atoms or molecules in a definite amount of the substance.
↪ It is found that the number of atoms present in 1 gram atom of any element is equal to the number of molecules present in 1 g molecule of any substance.
↪ This number has been determined and found to be equal to 6.023 x 1023 . It is called Avogadro's Number.
↪ Avogadro's number may be defined as the number of atoms present in one gram atom of the element or the number of molecules present in one gram molecules of the substance.
↪ The amount of substance containing Avogadro's number of atoms or molecules is called a mole (or simply written as mol).
↪ Thus, mole is defined as the amount of substance which contains the same number of discrete particles as the number of atoms present in 12 g of Carbon (C12).
⁕ Significance of a Mole
a. A mole gives the number of particles
↪ A mole contains Avogadro's number of discrete particles and it is equal to 6.023 x 1023.
1 mol of hydrogen atoms = 6.023 x 1023 hydrogen atoms
1 mol of hydrogen molecules = 6.023 x 1023 hydrogen molecules
1 mol of H2 molecules contain 2 mol of H atoms.
i.e. 6.023 x 1023 H2 molecules contain 2 x 6.023 x 1023 H atoms
1 mol of sodium ions = 6.023 x 1023 sodium ions
1 mol of electrons = 6.023 x 1023 electrons
↪ Therefore, the number of moles and the number of discrete particles are related as
b. A mole gives the mass of a substance in gram.
↪ A mole is that amount of substance which has mass equal to gram atomic mass if the substance is molecular.
In other words,
↪ One mole of atoms = 6.023 x 1023 atoms = Gram atomic mass of the element (molar mass of 1 mol of atoms)
For example: 1 mol of carbon atom = 6.023 x 1023 atoms of carbon = 12 g
1 mol of sodium atom = 6.023 x 1023 atoms of sodium = 23 g
1 mol of oxygen atom = 6.023 x 1023 atoms of oxygen = 16 g
1 mol of molecules = 6.023 x 1023 molecules
= Gram molecular mass (molar mass of 1 mol of molecules)
1 mol of oxygen molecules = 6.023 x 1023 molecules of oxygen = 32 g
1 mol of water molecules = 6.023 x 1023 molecules of water = 18 g
1 mol of CO2 molecules = 6.023 x 1023 molecules of CO2 = 44g
↪ Here, the number of mole and mass in grams are related as
c. A mole gives the volume of vapor or gas
↪ In case of gases or vapors, a mole is the amount of the gas that a occupies a volume of 22.4 L at NTP.
↪ It means the volume occupied by 1 gram mole of an ideal gas or vapor at NTP is known as gram molecular volume (GMV) or simply molar volume which is 22.4 L.
For example: 1 mol of hydrogen gas = 22.4 L of hydrogen gas at NTP
1 mol of oxygen gas = 22.4 L of oxygen gas at NTP
1 mol of CO2 gas = 22.4 L of CO2 at NTP
↪ Here, the number of mole and volume of gas are related as