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Moles and molar mass

The mole is the chemical unit for amount of substance: one mole contains Avogadro's number, $6.022\times10^{23}$ , particles. Molar mass is the mass of one mole of a substance, in g/mol, found by summing atomic masses from the periodic table. Together they let you convert between number of moles and mass in grams.

n = \frac{m}{M}

number of moles from mass and molar mass

N = n\cdot N_A

number of particles,

N_A = 6.022\times10^{23}

/mol

Symbols

$n$	amount of substance	mol
$m$	mass	g
$M$	molar mass	g/mol
$N_A$	Avogadro's number	1/mol

Example

180 g CO2, $M = 44.01$ g/mol:

$n = 180/44.01 \approx 4.09$ mol.

Molar mass always has the unit g/mol — do not confuse it with atomic mass in u (which is numerically equal).

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Part of General Chemistry: Moles and stoichiometry.