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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

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