mole (chemistry)

All Sources -
Updated Media sources (1) About encyclopedia.com content Print Topic Share Topic
views updated

Mole

In chemistry, a mole is a certain number of particles, usually of atoms or molecules. In theory, one could use any number of different terms for counting particles in chemistry. For example, one could talk about a dozen (12) particles or a gross (144) of particles. The problem with these terms is that they describe far fewer particles than one usually encounters in chemistry. Even the tiniest speck of sodium chloride (table salt), for example, contains trillions and trillions of particles.

The term mole, by contrast, refers to 6.022137 × 1023 particles. Written out in the long form, it's 602,213,700,000,000,000,000,000 particles. This number is very special in chemistry and is given the name Avogadro's number, in honor of Italian chemist and physicist Amadeo Avogadro (17761856), who first suggested the concept of a molecule.

A unit like the mole (abbreviated mol) is needed because of the way chemists work with and think about matter. When chemists work in the laboratory, they typically handle a few grams of a substance. They might mix 15 grams of sodium with 15 grams of chlorine. But when substances react with each other, they don't do so by weight. That is, one gram of sodium does not react exactly with one gram of chlorine.

Instead, substances react with each other atom-by-atom or molecule-by-molecule. In the above example, one atom of sodium combines with one atom of chlorine. This ratio is not the same as the weight ratio because one atom of sodium weighs only half as much as one atom of chlorine.

The mole unit, then, acts as a bridge between the level on which chemists actually work in the laboratory (by weight, in grams) and the way substances actually react with each other (by individual particles, such as atoms). One mole of any substanceno matter what substance it isalways contains the same number of particles: the Avogadro number of particles.

Think of what this means in the reaction between sodium and chlorine. If a chemist wants this reaction to occur completely, then exactly the same number of particles of each must be added to the mixture. That is, the same number of moles of each must be used. One can say: 1 mole of sodium will react completely with 1 mole of chlorine. It's easy to calculate a mole of sodium; it is the atomic weight of sodium (22.98977) expressed in grams. And it's easy to calculate a mole of chlorine; it is the molecular weight of chlorine (70.906) expressed in grams. This conversion allows the chemist to weigh out exactly the right amount of sodium and chlorine to make sure the reaction between the two elements goes to completion.

views updated

Mole

In chemistry, a mole is 6.022137 × 1023 particles, usually atoms or molecules. This number, usually shortened to 6.02 × 1023, is known as Avogadros number in honor of Count Amedeo Avogadro (1776-1856), an Italian professor of chemistry and physics at the University of Turin who was the first person to distinguish in a useful way between atoms and molecules.

A standard unit for counting numbers of particles is needed in chemistry, because atoms and molecules react with one another particle by particle. The amount of a chemical reactionhow much of the chemicals are used up or producedis determined by the numbers of particles that are reacting. Weighing the chemicals would not reveal meaningful information without a way to translate weights into numbers of atoms or molecules.

The mole is the translation factor between weights and numbers of particles. One mole of any substance weighs a number of grams that is equal to the atomic or molecular weight of that substance. Thus, if the atomic weights of iron and silver are 55.85 and 107.9, respectively, then 1.95 oz (55.85 g) of iron and 3.78 oz (107.9 g) of silver each contains 6.02 × 1023 atoms. Putting it the other way, a mole of iron (that is, 6.02 × 1023atoms of iron) would weigh 1.95 oz (55.85 g), while a mole of silver would weigh 3.78 oz (107.9 g).

Iron and silver are elements, and are made up of atoms. Sodium chloride (table salt) and sucrose (cane sugar), on the other hand, are compounds, and are made up of molecules. Nevertheless, the mole still works: a mole of salt or sugar means 6.02 × 1023molecules of them. The molecular weights of salt and sugar are 58.45 and 342.3, respectively. Thus, 2.05 oz (58.45 g) of salt and 11.98 oz (342.3 g) of sugar contain the same number of molecules: 6.02 × 1023.

Robert L. Wolke

views updated

mole1 / mōl/ • n. 1. a small burrowing insectivorous mammal (family Talpidae) with dark velvety fur, a long muzzle, and very small eyes. Its several species include the eastern mole (Scalopus aquaticus) of North America. 2. a spy who achieves over a long period an important position within the security defenses of a country. ∎  someone within an organization who anonymously betrays confidential information. mole2 / mōl/ • n. a small, often slightly raised blemish on the skin made dark by a high concentration of melanin. mole3 / mōl/ • n. a large solid structure on a shore serving as a pier, breakwater, or causeway. ∎  a harbor formed or protected by such a structure. mole4 / mōl/ • n. Chem. the SI unit of amount of substance, equal to the quantity containing as many elementary units as there are atoms in 0.012 kg of carbon-12. mole5 / mōl/ • n. Med. an abnormal mass of tissue in the uterus. See also hydatidiform mole.

views updated

Mole

In chemistry , a mole is a certain number of particles, usually of atoms or molecules. Just as a dozen particles (abbreviated doz.) would be 12 of them, a mole of particles (abbreviated mol) is 6.022137 × 1023 of them. This number, usually shortened to 6.02 × 1023, is known as Avogadro's number in honor of Count Amedeo Avogadro (1776-1856), an Italian professor of chemistry and physics at the University of Turin who was the first person to distinguish in a useful way between atoms and molecules. It is such a huge number (more than 600 billion trillion) because atoms and molecules are so incredibly tiny that we must have huge numbers of them before we can do anything useful with them.

A standard unit for counting numbers of particles is needed in chemistry, because atoms and molecules react with one another particle by particle. The amount of a chemical reaction—how much of the chemicals are used up or produced—is determined by the numbers of particles that are reacting. Weighing the chemicals wouldn't tell us anything very meaningful unless we knew how to translate those weights into actual numbers of atoms or molecules. For example, if one mole of substance A requires one mole of substance B to react with completely, we need to know how much of substance B to weigh out in order to have just the right amount, without any shortage or waste.

The mole is the translation factor between weights and numbers of particles. One mole of any substance weighs a number of grams that is equal to the atomic or molecular weight of that substance. Thus, if the atomic weights of iron and silver are 55.85 and 107.9, respectively, then 1.95 oz (55.85 g) of iron and 3.78 oz (107.9 g) of silver each contains 6.02 × 1023 atoms. Putting it the other way, a mole of iron (that is, 6.02 × 1023 atoms of iron) would weigh 1.95 oz (55.85 g), while a mole of silver would weigh 3.78 oz (107.9 g).

Iron and silver are elements, and are made up of atoms. Sodium chloride (table salt ) and sucrose (cane sugar), on the other hand, are compounds, and are made up of molecules. Nevertheless, the mole still works: a mole of salt or sugar means 6.02 × 1023molecules of them. The molecular weights of salt and sugar are 58.45 and 342.3, respectively. Thus, 2.05 oz (58.45 g) of salt and 11.98 oz (342.3 g) of sugar contain the same number of molecules: 6.02 × 1023.

Robert L. Wolke

views updated

MOLE

MOLE , rodent. The only mole found in Israel is the mole rat (Spalax ehrenbergi), a small mammal belonging to the order Rodentia. It is blind, its rudimentary eyes being covered with a membrane. Inhabiting subterranean burrows which it digs, it throws up the ground in a continuous series of mounds. Sometimes it builds a nest in a small mound. Into these burrows, Isaiah prophesied (2:20) a man would cast away "his idols of silver, and his idols of gold… to the moles and to the bats," the biblical word here for "moles," ḥafor perot, denoting a burrower in Aramaic (pina, i.e., "burrower"). According to another opinion ḥafor perot refers to an animal which digs up fruits in the ground. In talmudic literature the mole rat is called eishut which, because of the damage it causes to crops, may be hunted also on the intermediate days of a festival (mk 1:4). The word eshet, which occurs in Psalms (58:9) in a reference to those "that have not seen the sun," has been identified by some with eishut, i.e., mole rats "which do not see the sun but burrow in the ground and live there" (Mid. Ps. to 58:9). In modern Hebrew the mole rat is called ḥoled, mentioned among the unclean creeping things (Lev. 11:29). The biblical ḥoled, however, is the *rat.

The identification of ḥafor perot with the mole rat is most plausible. However, some scholars believe that it is a kind of bat (cf. Tur-Sinai, in: Leshonenu, no. 26, 77ff.), and S. Lieberman holds that it is the "flying fox" (which is not found in Israel) or the fruit bat (cf. Leshonenu, no. 29, 132f.).

bibliography:

Lewysohn, Zool, 101, no. 135; J. Feliks, The Animal World of the Bible (1962), 43; M. Dor, Leksikon Zo'ologi (1965), 121.

[Jehuda Feliks]

views updated

molebarcarole, bole, bowl, cajole, coal, Cole, condole, console, control, dhole, dole, droll, enrol (US enroll), extol, foal, goal, hole, Joel, knoll, kohl, mol, mole, Nicole, parol, parole, patrol, pole, poll, prole, rôle, roll, scroll, Seoul, shoal, skoal, sole, soul, stole, stroll, thole, Tirol, toad-in-the-hole, toll, troll, vole, whole •Creole •carriole, dariole •cabriole • capriole •aureole, gloriole, oriole •wassail-bowl • fishbowl • dustbowl •punchbowl • rocambole • farandole •girandole • manhole • rathole •armhole • arsehole • hellhole •keyhole, kneehole •peephole •sinkhole • pinhole • cubbyhole •hidey-hole • pigeonhole •eyehole, spyhole •foxhole •knothole, pothole •borehole, Warhol •porthole • soundhole • blowhole •stokehole • bolthole • loophole •lughole, plughole •chuckhole • buttonhole • bunghole •earhole • waterhole • wormhole •charcoal • caracole • Seminole •pinole

views updated

mole, in chemistry, a quantity of particles of any type equal to Avogadro's number, or 6.02×1023 particles. One gram-molecular weight of any molecular substance contains exactly one mole of molecules. The term mole is often used in place of gram-molecular weight; e.g., one speaks of 18 grams of water as one mole of water rather than as one gram-molecular weight of water. The mole is a unit in the International System of Units (SI).

views updated

mole in proverbial use often referred to as the type of a blind creature. The mole was also toasted by Jacobites as the little gentleman in black velvet, in reference to the death of William III, said to have been caused by a fall from his horse which had stumbled on a molehill (the small mound of earth thrown up by a mole burrowing near the surface).

From the early 1920s, mole has been used allusively to designate a spy who achieves over a long period an important position within the security defences of a country, or someone within an organization who anonymously betrays confidential information.

See also make a mountain out of a molehill.

views updated

mole The amount of a substance containing as many elementary units as there are carbon atoms in 12 g of carbon-12 (i.e. the Avogadro number). The elementary units by which the amount of substance is being measured may be atoms, molecules, ions, electrons, radicals, or any other expressly named constituent.

views updated

mole Symbol mol. The SI unit of amount of substance. It is equal to the amount of substance that contains as many elementary units as there are atoms in 0.012 kg of carbon–12. The elementary units may be atoms, molecules, ions, radicals, electrons, etc., and must be specified. 1 mole of a compound has a mass equal to its relative molecular mass expressed in grams.