Mole | |
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Unit system | SI base unit |
Unit of | Amount of substance |
Symbol | mol |
The mole is the unit of measurement in the International System of Units (SI) for amount of substance. The unit is defined as the amount of a chemical substance that contains as many representative particles, e.g., atoms, molecules, ions, electrons, or photons, as there are atoms in 12 grams of carbon-12 (12C), the isotope of carbon with standard atomic weight 12 by definition. This number is expressed by the Avogadro constant, which has a value of 140857×1023 mol−1, which is just over 602 sextillion ( 6.022thousand million million million). The mole is one of the base units of the SI, and has the unit symbol mol.
The mole is widely used in chemistry as a convenient way to express amounts of reactants and products of chemical reactions. For example, the chemical equation 2 H2 + O2 → 2 H2O implies that 2 moles of dihydrogen (H2) and 1 mole of dioxygen (O2) react to form 2 moles of water (H2O). The mole may also be used to express the number of atoms, ions, or other elementary entities in a given sample of any substance. The concentration of a solution is commonly expressed by its molarity, defined as the number of moles of the dissolved substance per litre of solution.