Mole (unit)

The mole (symbol mol) is a <a href="/facts/Unit_of_measurement/pvTpWbmC">unit of measurement</a>, the <a href="/facts/SI_base_unit/M7PsTWg4">base unit</a> in the <a href="/facts/International_System_of_Units/S7YLglNz">International System of Units</a> (SI) for <a href="/facts/Amount_of_substance/tQVyNLCp">amount of substance</a>, an SI base quantity proportional to the <a href="/facts/Particle_number/jqVeDoIl">number of elementary entities</a> of a substance. One mole is an aggregate of exactly 6.02214076×1023 elementary entities (approximately 602 <a href="/facts/Sextillion/J8c2407m">sextillion</a> or 602 billion times a trillion), which can be <a href="/facts/Atom/69syB8dH">atoms</a>, <a href="/facts/Molecule/N9ljSfFq">molecules</a>, <a href="/facts/Ion/wrbwhF3z">ions</a>, <a href="/facts/Ion_pair/dacS8wXj">ion pairs</a>, or other <a href="/facts/Particle/JHKr2w6h">particles</a>. The number of particles in a mole is the Avogadro number (symbol N0) and the numerical value of the <a href="/facts/Avogadro_constant/SwajCq22">Avogadro constant</a> (symbol NA) expressed in mol−1. The relationship between the mole, Avogadro number, and Avogadro constant can be expressed in the following equation:
 
 
 
 1
 
  mol
 
 =
 
 
 
 N
 
 0
 
 
 
 N
 
 A
 
 
 
 
 =
 
 
 
 6.02214076
 ×
 
 10
 
 23
 
 
 
 
 N
 
 A
 
 
 
 
 
 
 {\displaystyle 1{\text{ mol}}={\frac {N_{0}}{N_{\text{A}}}}={\frac {6.02214076\times 10^{23}}{N_{\text{A}}}}}
 
The current SI value of the mole is based on the historical definition of the mole as the amount of substance that corresponds to the number of atoms in 12 <a href="/facts/Gram/CNAPqWKz">grams</a> of <a href="/facts/Carbon-12/nJYECzEr">12C</a>, which made the <a href="/facts/Molar_mass/m2laJErl">molar mass</a> of a compound in grams per mole, numerically equal to the average <a href="/facts/Molecular_mass/FWueGMed">molecular mass</a> or formula mass of the compound expressed in <a href="/facts/Dalton_(unit)/IMATU3vf">daltons</a>. With the <a href="/facts/2019_revision_of_the_SI/g0h07jCX">2019 revision of the SI</a>, the numerical equivalence is now only approximate, but may still be assumed with high accuracy. 
Conceptually, the mole is similar to the concept of <a href="/facts/Dozen/CAzsA8F7">dozen</a> or other convenient grouping used to discuss collections of identical objects. Because laboratory-scale objects contain a vast number of tiny atoms, the number of entities in the grouping must be huge to be useful for work.
The mole is widely used in <a href="/facts/Chemistry/SrNqkGVm">chemistry</a> as a convenient way to express amounts of <a href="/facts/Reactant/c3GLInCu">reactants</a> and amounts of <a href="/facts/Product_(chemistry)/8uCoDUdv">products</a> of <a href="/facts/Chemical_reaction/GpqWlKrz">chemical reactions</a>. For example, the chemical equation 2 H2 + O2 → 2 H2O can be interpreted to mean that for each 2 mol <a href="/facts/Dihydrogen/BoYHjl0J">molecular hydrogen</a> (H2) and 1 mol <a href="/facts/Dioxygen/UVNYnKUQ">molecular oxygen</a> (O2) that react, 2 mol of water (H2O) form. The <a href="/facts/Concentration/wqBmz5od">concentration</a> of a solution is commonly expressed by its <a href="/facts/Molar_concentration/P2WL5b9q">molar concentration</a>, defined as the amount of dissolved substance per unit volume of solution, for which the unit typically used is mole per <a href="/facts/Litre/QKwbQz8I">litre</a> (mol/L).

Mole (unit) open-in-new

Mole (unit)