Mole (unit)

The mole is a unit of measurement in chemistry, which relates the number of entities (atoms, molecules, or ions) to the mass of the material. Chemical reaction formulae are expressed in molecules and atoms, which are impractical to measure or count directly. However, as the atomic weight of any given atom is constant, and generally known, it is possible to quantify the amount of substance by measuring the weight in grams, and dividing by the molecular weight of the molecule (the sum of the atomic weights of the individual atoms in the molecule), which yields the number of moles in the sample weighed.

Technically, a mole is defined in the SI as the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon-12. A mole of a substance has a mass in grams which is equal to the mass of a single atom or molecule of the substance in atomic mass units. The number of entities (atoms or molecules) of a substance in one mole is known as Avogadro's constant, which is approximately 6.022 141 5 × 10²³.

One mole of an ideal gas occupies 22.414 litres at "standard temperature and pressure" (273.15K and 101.325 kPa).

The word "mole" is shortened from "gram molecular weight", the original term. Industrial chemists also used a "kilogram molecular weight", equal to 1000 mole.

Notes

Sources

• mole. Sizes.com (2006-11-07). Retrieved on 2007-05-11.