Mole

Mole Concept

Term mole was suggested by Ostwald (Latin word mole = heap)

A mole is defined as the amount of substance which contains same number of elementary particles (atoms, molecules or ions) as the number of atoms present in 12 g of carbon (C-12).

1 mol = 6.023 * 1023 atoms = one gram-atom = gram atomic mass

1 mol = 6.023 * 1023 molecules = gram molecular mass

In gaseous state at STP (T = 273 K, p = 1 atm)

Gram molecular mass = 1 mol

= 22.4 L = 6.022 * 1023 molecules

Standard number 6.023x 1023 is called Avogadro number in honour of Avogadro (he did not give this number) and is denoted by NA.

The volume occupied by one mole molecules of a gaseous substance is called molar volume or gram molecular volume.

Number of moles = amount of substance (in gram) / molar mass

Number of molecule = number of moles * NA

Number of molecules in Ig compound = NA / g-molar mass

Number of molecules in 1 cm3 (1 mL) of an ideal gas at STP is called Loschmidt number (2.69x 1019).

[One amu or u (unified mass) is equal to exactly the 1 / 12th of the mass of 12C atom, i.e., 1 amu or u = 1 / 12 * mass of one carbon (C12) atom

1 amu = 1 / NA

= 1 Dalton = 1.66x 10-24 g

One mole of electrons weighs 0.55 mg (5.5x 10-4 g).