Mole (unit)

Mole is the SI unit of measurement used to measure the number of things, usually atoms or molecules. One mole of something is equal to Avogadro's number.

The measurement of Avogadro's number was refined in 2011 to 6.02214078×1023 ± 0.00000018×1023. [1]

Scientists use this number because it is the number of carbon atoms in 12 grams of carbon-12, which is the most common kind of carbon. Anything can be measured in moles, but it is not practical for most tasks because the value is so massive. For example, one mole of grapefruits would be as big as the earth.

The number does not lend itself to easy expression in words. The nearest "casual" number is one million-million-million-million, which is 1024.

Because different molecules and atoms do not have the same mass, one mole of one thing does not weigh the same as one mole of something else. Atoms and molecule mass is measured in u. One u is equal to one gram per mole. This means that if an atom has a mass of one u, one mole of this atom weighs one gram.

Mathematics with the mole

Moles = mass (g) / Relative mass (grams per mole) Example: How many moles are there in 20 grams of hydrogen? A value of 1 can be used for hydrogen's relative mass, although the correct value is slightly larger. So: moles = mass/relative mass = 20/1 = 20 moles.

Moles = concentration (mol/dm3) x volume (dm3) Example: How many moles are there in 100cm3 of 0.1M H2SO4? 1 dm3 is the same as 1000 cm3, so the value in cubic centimetres needs to be divided by 1000. 100/1000 x 0.1 = 0.01 moles.

A methane molecule is made from one carbon atom and four hydrogen atoms. Carbon has a mass of 12.011 u and hydrogen has a mass of 1.008 u. This means that the mass of one methane molecule is 12.011 u + (4*1.008u), or 16.043 u. This means that one mole of methane has a mass of 16.043 grams.

A mole can be thought of as two bags of different sized balls. One bag contains 3 tennis balls and the other 3 footballs. There is the same number of balls in both bags but the mass of the footballs is much larger. It is a different way to measure things. Moles measure the number of particles, not the mass. So both bags contain three moles.

A mole is simply a unit of the number of things. Other common units include a dozen, meaning  12, and a score, meaning 20. Similarly, a mole refers to a specific quantity-- its distinguishing feature is that its number is far larger than other common units. Such units are typically invented when existing units can not describe something easily enough. Chemical reactions typically take place between molecules of varying weights, meaning measurements of mass (such as grams) can be misleading when compared the reactions of individual molecules. On the other hand, using the absolute number of atoms/molecules/ions would also be confusing, as the massive numbers involved would make it all too easy to misplace a value or drop a digit. As such, working in moles allows scientists to refer to a specific quantity of molecules or atoms without resorting to excessively large numbers.

Other Languages
العربية: مول
asturianu: Mol
azərbaycanca: Mol
Bân-lâm-gú: Mol
беларуская: Моль
беларуская (тарашкевіца)‎: Моль
български: Мол
བོད་ཡིག: མོལ།
bosanski: Mol (jedinica)
brezhoneg: Mol
català: Mol
Чӑвашла: Моль
čeština: Mol
Cymraeg: Môl (uned)
Deutsch: Mol
eesti: Mool
Ελληνικά: Γραμμομόριο
English: Mole (unit)
español: Mol
Esperanto: Molaro (kemio)
euskara: Mol
فارسی: مول
français: Mole (unité)
Gaeilge: Mól
galego: Mol
한국어: 몰 (단위)
Հայերեն: Մոլ
हिन्दी: मोल (इकाई)
Bahasa Indonesia: Mol
íslenska: Mól
italiano: Mole
עברית: מול
ಕನ್ನಡ: ಮೋಲ್
ქართული: მოლი
қазақша: Моль
Kreyòl ayisyen: Mòl
Kurdî: Mol
Кыргызча: Моль
latviešu: Mols
Lëtzebuergesch: Mol
lietuvių: Molis (vienetas)
Ligure: Mole
magyar: Mól
македонски: Мол (единица)
मराठी: मोल (एकक)
Bahasa Melayu: Mol
монгол: Моль
Nederlands: Mol (eenheid)
日本語: モル
Nordfriisk: Mol
norsk nynorsk: Mol
occitan: Mòl (unitat)
ਪੰਜਾਬੀ: ਮੋਲ (ਇਕਾਈ)
پنجابی: مول
Piemontèis: Mòle
Plattdüütsch: Mol (Eenheit)
polski: Mol
português: Mol
română: Mol
русиньскый: Мол
русский: Моль
සිංහල: මවුලය
slovenčina: Mol (jednotka SI)
slovenščina: Mol (enota)
Soomaaliga: Mole
српски / srpski: Мол (јединица)
srpskohrvatski / српскохрватски: Mol (jedinica)
suomi: Mooli
svenska: Mol
Tagalog: Mole (yunit)
தமிழ்: மோல்
татарча/tatarça: Моль
ไทย: โมล
Türkçe: Mol (birim)
українська: Моль (одиниця)
Tiếng Việt: Mol
文言: 摩爾
Winaray: Mol
粵語: 摩爾