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How do you calculate the moles of a substance?

The mole is the amount of a substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon-12; its symbol is 'mol." When the mole is used, the elementary entities must be specified and may be atoms. One mole is the Avogadro number of particles (atoms, molecules, ions or electrons) in a substance.

1 Answer

In order to calculate the moles of a substance, you need to know the mass of the substance and its molar mass. Molar mass is the atomic weight in grams/mol.

One Mole Of A Substance Is Equal To

Example:
How many moles of copper(II) sulfate, #'CuSO'_4#, are in #'250.0g CuSO'_4#?

Molar Mass of #'CuSO'_4#
Subscript x molar mass =
1 x 63.456g/mol Cu = 63.456g/mol Cu
1 x 32.065g/mol S = 32.065g/mol S
4 x 15.999g/mol O = 63.996g/mol O
Total: 159.517g/mol

1mol #'CuSO'_4# = 159.517g #'CuSO'_4#, which gives us two conversion factors:

#'1mol CuSO'_4/'159.517g CuSO'_4'# and #'159.517g CuSO'_4/'1mol CuSO'_4#

One Mole Of A Substance

Now multiply the known mass x the conversion factor with moles on top and grams on bottom. This will cancel the grams and leave the moles.

One Mole Of A Substance Contains

#'250.0g CuSO'_4# x #'1mol CuSO'_4/'159.517g CuSO'_4'# = #'1.567mol CuSO'_4#

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