Mole and the Avagadro's Number
The mole is the SI base unit for an amount of a substance.
The SI unit for amount of substance is the mole , defined as
- the amount of substance that has an equal number of elementary entities as there are atoms in 12 g of carbon-12 (12C - the isotope of carbon with standard atomic weight 12 by definition).
That number of elementary entities in carbon-12 is the Avogadro constant (number) NA.
NA = 6.022141×1023 (molecules/mol)
The mole is one of the base units of the SI, and has the unit symbol (mol) .
Standard volume of 1 mole of an ideal gas at 1 atmosphere and 0°C is 22.414 liters.
See also Molecular Weight - Common Substances
Example: Number of molecules in 1 mole of hydrogen gas.
Hydrogen gas contains H2molecules. 1 mole of a substance is 6.022141 ×1023 molecules of the substance.
So; 1 mole of hydrogen gas contains 6.022141 ×1023 H2-molecules
Example: Number of molecules in ethyl alcohol
The molecular weight of ethyl alcohol is 46.07 kg/kmol and the number of molecules in 1 kg can be calculated as
n = ((1 kg) / (46.07 kg/kmol)) (6.022×1023 molecules/mol) (1000 mol/kmol)
= 1.31 1025 molecules
