Share on Facebook Share on Twitter Email
Answers.com

mole

 
Dictionary: mole5   (mōl) pronunciation
Home > Library > Literature & Language > Dictionary
n. (Abbr. mol)
  1. The amount of a substance that contains as many atoms, molecules, ions, or other elementary units as the number of atoms in 0.012 kilogram of carbon 12. The number is 6.0225 × 1023, or Avogadro's number. Also called gram molecule.
  2. The mass in grams of this amount of a substance, numerically equal to the molecular weight of the substance. Also called gram-molecular weight.

[German Mol, short for Molekulargewicht, molecular weight, from molekular, molecular, from French moléculaire, from molécule, molecule. See molecule.]


Search unanswered questions...

Enter a question here...
Search: All sources Community Q&A Reference topics

Sci-Tech Encyclopedia: Mole
Top
Home > Library > Science > Sci-Tech Encyclopedia

A unit (symbolized mol) used to measure the amount of material in a chemical sample. The mole is defined by international agreement as the amount of substance (chemical amount) of a chemical system that contains as many molecules or entities as there are atoms in 12 g of carbon-12 (12C). When the mole is used, the elementary entities need not be molecules, but they must always be specified. They may be atoms, molecules, ions, electrons, or specified groups of such particles.

Three obvious ways of measuring the amount of material in a given sample are to measure the mass of the sample, to measure the volume, or to count the number of molecules in the sample. Although it is more difficult to devise an experiment to count molecules, this third way of measuring amount is of special interest to chemists because molecules react in simple rational proportions (for example, one molecule of A may react with one, or two, or three molecules of B, and so forth). However, to count molecules is inconvenient in practice because the numbers are so large. For any chemical, a mass of 1 kilogram of the sample contains a large number of molecules, of the order 1023–1024. The mole is defined so that 1 mole of any substance always contains the same number of molecules. This number approximately 6.02 × 1023, and is known as the Avogadro number. The mole is a more convenient unit in which to measure the amount of a chemical than counting the number of molecules, and it has the same advantages. See also Avogadro number.

The amount of substance (chemical amount) of a sample, n, may be determined in practice by one of three methods.

The value of n (the amount of substance) may be determined from the mass m by dividing by the molar mass M of the sample, as in Eq. (1). If m is expressed in g and M in g/mol, then the value of n will be obtained in mol.
1. n=\frac{m}{M}

For a gas, the value of n may be determined from the volume V, pressure p, and absolute temperature T by using the ideal gas equation (2), where R is the gas constant
2. n=\frac{pV}{RT}
(R = 8.3145 J K−1 mol−1). If pV is expressed in (N m−2) × (m3) = J, and RT in J mol−1, then pV/RT gives the value of n in mol.

For a solution, the amount of solute (or the amount concentration of solution) is frequently determined by titration: if νA molecules of A react with νB molecules of B in the titration, then at the end point the amount of A used (nA) is related to the amount of B (nB) by Eq. (3), so that if one is known the other may be determined.
3. n_A=\frac{\nu_A}{\nu_B}n_B
See also Titration.

The concentration of a solution may be recorded as (mass of solute)/(volume of solution), in units gram/liter; or as (chemical amount of solute)/(volume of solution) in units mol/liter. Because of the proportionality of chemical amount to number of molecules, the latter is the more useful measure of concentration and is generally used in chemistry and biochemistry. See also Concentration scales.

Computer Desktop Encyclopedia: mole
Top
Home > Library > Technology > Computer Encyclopedia

A unit of measurement of molecular weight. Part of the SI system of measurement, one mole (mol) is equal to 6.02257 X 10 to the 23rd molecules. See SI units.

Download Computer Desktop Encyclopedia to your iPhone/iTouch

Measures and Units: mole
Top
Home > Library > Science > Measures and Units

[Etymology: molecule] chemistry. Symbol mol. SI The base unit for an amount of a substance: the amount of a substance that contains as many of its basic entities (e.g. atoms for chemical elements, molecules for compounds) as there are atoms in 12 g of 12C.
[McGlashan M. L. Metrologia Vol. 31, 247-55 (1995)]

The relevant basic entity should be defined or clearly implied in any expression of mole measurement; besides the common atom and molecule, it can be ions, electrons, or other ‘elementary’ particles, or groups of such particles. For any pure substance, one mole has a mass in grams numerically equal to its molecular weight in daltons. (Despite the change in metric systems from gram to kilogram as the base unit for mass, the mole remains tied in this manner to the gram. This is sometimes emphasized by calling it the gram-mole, allowing the kilogram-mole to mean its SI- coherent thousand-fold multiple.)

The number of molecules of any substance, else, for an element, of atoms, contained in 1 mole of it is Avogadro's number, = 602.213 67(36) × 1021. This could provide a natural definition of the mole independent of the kilogram and, using the masses of electron, neutron, and proton, a natural definition of that unit of mass too.

See also dalton.

History

Originally introduced early in the 1900s as the gram-molecular weight, i.e. the number of grams of a substance that equalled its molecular weight, it was then defined as the amount of substance of a system which contains as many atoms as 16 g of oxygen; called also gram-molecule. However, this proved ambiguous because physicists interpreted it as referring to the common isotope of oxygen, while chemists used the heavier naturally occurring and somewhat variable mixture of isotopes 16, 17, and 18. In 1940 the International Commission on Atomic Weights standardized the ratio as being 1:1.000 275, then brought in the unifying carbon-based scheme in 1961.
[Wichers E. Nature Vol. 194, 621-4 (1962)] This gave values of 0.0043% less than the chemists', and 0.0315% less than the physicists'. The carbon base results in more elements having integer values than applied with oxygen, whose scale had similar merit over hydrogen.

See weight re usage of that word.

1950/60‘relative amount of substance’ based on carbon 12.
1967CIPM; 1969 CIPM; 1971 14th CGPM:
‘1. The mole is the amount of substance of a system which contains as many atoms as 0.012 kilogram of carbon 12: its symbol is “mol”.
2. When the mole is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles.
3. The mole is a base unit of the International System of Units.’
1980CIPM: ‘in this definition, it is understood that unbound atoms of carbon, at rest and in their ground state, are referred to.’see note below

[Le Système International d'Unités (Sèvres, France: Bureau International de Poids et Mesures, 1985)]

Britannica Concise Encyclopedia: mole
Top
Home > Library > Miscellaneous > Britannica Concise Encyclopedia

Standard unit for measuring everyday quantities of such minute entities as atoms or molecules. For any substance, the number of atoms or molecules in a mole is Avogadro's number (6.02 ´ 1023) of particles. Defined exactly, it is the amount of pure substance containing the same number of chemical units that there are in exactly 12 g of carbon-12. For each substance, a mole is its atomic weight, molecular weight, or formula weight in grams. The number of moles of a solute in a litre of solution is its molarity (M); the number of moles of solute in 1,000 g of solvent is its molality (m). The two measures differ slightly and have different uses. See also stoichiometry.

For more information on mole, visit Britannica.com.

Sports Science and Medicine: mole
Top
Home > Library > Health > Sports Science and Medicine

The SI unit of amount of a substance expressed as its molecular weight in grams. Thus, 1 mole (M) of glucose, which has the formula C6H12O6, weighs 180 g. where the atomic weight of carbon is 12, hydrogen 1, and oxygen 16.

 
Columbia Encyclopedia: mole
Top
Home > Library > Miscellaneous > Columbia Encyclopedia
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).

Science Q&A: What is a mole in chemistry?
Top
Home > Library > Science > Science Q&A

A mole (symbol mol), a fundamental measuring unit for the amount of a substance, refers to either a gram atomic weight or a gram molecular weight of a substance. It is the quantity of a substance that contains 6.02 1023 atoms, molecules, or formula units of that substance. This number is called Avogadro's number or constant after Amadeo Avogadro (1776-1856), who is considered to be one of the founders of physical science.

Previous question: How did the electrical unit watt originate?
Next question: What is Mole Day?

Obscure Words: mole
Top
Home > Library > Literature & Language > Obscure Words


Chem.  the molecular weight of a substance expressed in grams; gram molecule
Wikipedia: Mole (unit)
Top
Home > Library > Miscellaneous > Wikipedia
This article is about the SI unit. For other uses, see Mole (disambiguation).

The mole (symbol: mol) is a unit of amount of substance: it is an SI base unit,[1] and one of the few units used to measure this physical quantity. The name "mole" was coined in German (as Mol) by Wilhelm Ostwald in 1893,[2] although the related concept of equivalent mass had been in use at least a century earlier. The name is assumed to be derived from the word Molekül (molecule). The first usage in English dates from 1897, in a work translated from German.[3][4] The names gram-atom and gram-molecule have also been used in the same sense as "mole",[1][5] but these names are now obsolete.

The mole is defined as the amount of substance of a system that contains as many "elementary entities" (e.g. atoms, molecules, ions, electrons) as there are atoms in 12 g of carbon-12 (12C).[1] A mole has 6.0221415×1023[6] atoms or molecules of the pure substance being measured. A mole will possess mass exactly equal to the substance's molecular/atomic weight in grams. Because of this, one can measure the number of moles in a pure substance by weighing it and comparing the result to its molecular/atomic weight.

The current definition of the mole was approved during the 1960s:[1][5] Prior to that, there had been definitions based on the atomic weight of hydrogen (about one gram of hydrogen-1 gas, excluding its heavy isotopes), the atomic weight of oxygen, and the relative atomic mass of oxygen-16: the four different definitions are equivalent to within 1%.

The most common method of measuring an amount of substance is to measure its mass and then to divide by the molar mass of the substance.[7] Molar masses may be easily calculated from tabulated values of atomic weights and the molar mass constant (which has a convenient defined value of 1 g/mol). Other methods include the use of the molar volume or the measurement of electric charge.[7]

Contents

The mole as a unit

Since its adoption into the International System of Units, there have been a number of criticisms of the concept of the mole being a unit like the metre or the second.[5] These criticisms may be briefly summarised as:

  • amount of substance is not a true physical quantity (or dimension), and is redundant to mass, so should not have its own base unit;
  • the mole is simply a shorthand way of referring to a large number.

In chemistry, it has been known since Proust's Law of definite proportions (1794) that knowledge of the mass of each of the components in a chemical system is not sufficient to define the system. Amount of substance can be described as mass divided by Proust's "definite proportions", and contains information which is missing from the measurement of mass alone. As demonstrated by Dalton's Law of partial pressures (1803), a measurement of mass is not even necessary to measure the amount of substance (although in practice it is usual). There are many physical relationships between amount of substance and other physical quantities, most notably the ideal gas law (where the relationship was first demonstrated in 1857). The term "mole" was first used in a textbook describing these colligative properties.

The second misconception, that the mole is simply a counting aid, has even found its way into elementary chemistry textbooks.[8] These books and others often contend that the mole is defined in terms of the Avogadro constant, rather than the other way around, and so is equal to 6.0221415×1023 elementary entities.

Consider the measurement of one mole of silicon. As silicon is a solid at room temperature, the convenient method of measurement is weighing. By consulting published tables, it can easily be found that the atomic weight of silicon is 28.0855.[9] Multiplying by the molar mass constant Mu gives the molar mass in any desired mass units: assuming the measurement is to be made in grams, Mu = 1 g/mol, and so the molar mass of silicon is 28.0855 g/mol. Hence, 28.0855 g of silicon is equivalent to one mole of silicon, without the Avogadro constant ever having come into play.

Counting (or calculating) the number of atoms in 28.0855 g of silicon is one way of determining the Avogadro constant, NA, and a way which is currently receiving a lot of attention (see below) although, as of the 2006 CODATA values of the physical constants, it is not the most accurate. It is only a method of determining NA because it is known by other means that 28.0855 g of silicon is equivalent to one mole. Those other means are:

  • the very accurate determination of the ratios of the masses of each of the three silicon nuclides to the mass of an atom of carbon-12, in such a way that it is known that a silicon-28 atom is [27.976 926 5327(20)/12] times as massive as a carbon-12 atom;[9][10]
  • the determination of the isotopic abundance of silicon in the samples used to make the measurements, allowing the calculation of the atomic weight of silicon in each individual sample;
  • the definition of 12 g of carbon-12 atoms to be equivalent to one mole.

History

The first table of atomic weights was published by John Dalton (1766–1844) in 1805, based on a system in which the atomic weight of hydrogen was defined as 1. These atomic weights were based on the stoichiometric proportions of chemical reactions and compounds, a fact which greatly aided their acceptance: it was not necessary for a chemist to subscribe to atomic theory (an unproven hypothesis at the time) to make practical use of the tables. This would lead to some confusion between atomic weights (promoted by proponents of atomic theory) and equivalent weights (promoted by its opponents and which sometimes differed from atomic weights by an integer factor), which would last throughout much of the nineteenth century.

Jöns Jacob Berzelius (1779–1848) was instrumental in the determination of atomic weights to ever increasing accuracy. He was also the first chemist to use oxygen as the standard to which other weights were referred. Oxygen is a useful standard, as, unlike hydrogen, it forms compounds with most other elements, especially metals. However he chose to fix the atomic weight of oxygen as 100, an innovation which did not catch on.

Charles Frédéric Gerhardt (1816–56), Henri Victor Regnault (1810–78) and Stanislao Cannizzaro (1826–1910) expanded on Berzelius' work, resolving many of the problems of unknown stoichiometry of compounds, and the use of atomic weights attracted a large consensus by the time of the Karlsruhe Congress (1860). The convention had reverted to defining the atomic weight of hydrogen as 1, although at the level of precision of measurements at that time—relative uncertainties of around 1%—this was numerically equivalent to the later standard of oxygen = 16. However the chemical convenience of having oxygen as the primary atomic weight standard became ever more evident with advances in analytical chemistry and the need for ever more accurate atomic weight determinations.

Scale basis Scale basis
relative to 12C = 12		 Relative deviation
from the 12C = 12 scale
Atomic weight of hydrogen = 1 1.007 94(7) −0.788%
Atomic weight of oxygen = 16 15.9994(3) +37.5 ppm
Relative atomic mass of 16O = 16 15.994 914 6221(15) +318 ppm

Other units called "mole"

Chemical engineers use the concept extensively, but the unit is rather small for industrial use. For convenience in avoiding conversions, American engineers adopted the pound-mole (noted lb-mol or lbmol), which is defined is the number of entities in 12 lb of 12C. One lb-mol is equal to 453.59237 mol.[11]

In the metric system, chemical engineers once used the kilogram-mole (noted kg-mol), which is defined as the number of entities in 12 kg of 12-C, and often referred to the mole as the gram-mole (noted g-mol), when dealing with laboratory data.[11] However modern chemical engineering practice is to use the kilomole (kmol), which is identical to the kilogram-mole, but whose name and symbol adopt the SI convention for standard multiples of metric units.

Proposed future definition

Kilogram

As with other SI base units, there have been proposals to redefine the kilogram in such a way as to define some presently measured physical constants to fixed values. One proposed definition of the kilogram is:[12]

The kilogram is the mass of exactly (6.0221415×1023⁄0.012) unbound carbon-12 atoms at rest and in their ground state.

This would have the effect of defining the Avogadro constant to be precisely 6.0221415×1023 elementary entities per mole.

Holiday

October the 23 (10/23) is the holiday, "Mole Day", honoring the unit. The day is used because of the unit in the equation of 10 to the 23rd power.

See also

References

  1. ^ a b c d International Bureau of Weights and Measures (2006), The International System of Units (SI) (8th ed.), pp. 114–15, ISBN 92-822-2213-6, http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf 
  2. ^ Ostwald, Wilhelm (1893). Hand- und Hilfsbuch zur ausführung physiko-chemischer Messungen. Leipzig. p.  119. 
  3. ^ Helm, Georg (1897), The Principles of Mathematical Chemistry: The Energetics of Chemical Phenomena, transl. by Livingston, J.; Morgan, R., New York: Wiley, p. 6 
  4. ^ Some sources place the date of first usage in English as 1902. Merriam–Webster proposes an etymology from Molekulärgewicht (molecular weight).
  5. ^ a b c de Bièvre, P.; Peiser, H.S. (1992), "'Atomic Weight'—The Name, Its History, Definition, and Units", Pure Appl. Chem. 64 (10): 1535–43, doi:10.1351/pac199264101535, http://www.iupac.org/publications/pac/1992/pdf/6410x1535.pdf 
  6. ^ Mohr, Peter J.; Taylor, Barry N.; Newell, David B. (2008). "CODATA Recommended Values of the Fundamental Physical Constants: 2006". Rev. Mod. Phys. 80: 633–730. doi:10.1103/RevModPhys.80.633. http://physics.nist.gov/cuu/Constants/codata.pdf.  Direct link to value..
  7. ^ a b International Bureau of Weights and Measures. "Realising the mole." Retrieved 25 September 2008.
  8. ^ Kotz, John C.; Treichel, Paul M.; Townsend, John R. (2008), Chemistry and Chemical Reactivity (7th ed.), Brooks/Cole, ISBN 0495387037, http://cengagesites.com/academic/kotz.cfm?site=2719&section=home 
  9. ^ a b National Institute of Standards and Technology. "Atomic Weights and Isotopic Compositions for All Elements". http://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=&ascii=html&isotype=some. Retrieved 2008-09-25. 
  10. ^ It should be emphasised that relative atomic masses are measured as ratios of the masses of two nuclides. They cannot be measured (at least not to this level of accuracy) as absolute values of the mass of each nuclide in yoctograms.
  11. ^ a b Himmelblau, David (1996). Basic Principles and Calculations in Chemical Engineering (6 ed.). p. 17-20. ISBN 0-13-305798-4. 
  12. ^ Mills, Ian M.; Mohr, Peter J.; Quinn, Terry J.; Taylor, Barry N.; Williams, Edwin R. (2005). "Redefinition of the kilogram: a decision whose time has come". Metrologia 42: 71–80. doi:10.1088/0026-1394/42/2/001. http://www.iop.org/EJ/article/0026-1394/42/2/001/met5_2_001.pdf.  Abstract.
v • d • e
SI base units
Metre · Kilogram · Second · Ampere · Kelvin · Mole · Candela
SI derived units


This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)

Translations: Mole
Top
Home > Library > Literature & Language > Translations

Dansk (Danish)
1.
n. - [zool.] muldvarp

2.
n. - modermærke, skønhedsplet

3.
n. - mole, havnedæmning

4.
n. - mol

5.
n. - mola (vævssamling i livmoderen)

6.
n. - krydret sauce af mexicansk oprindelse med chokolade, chilier og krydderier

Nederlands (Dutch)
mol, golfbreker, geheim agent, beschutte haven, moedervlek, mol (scheikunde)

Français (French)
1.
n. - (Zool) taupe, (fig) taupe

2.
n. - grain de beauté

3.
n. - jetée, brise-lames

4.
n. - (Phys, Chim) mole

5.
n. - (Méd) môle

6.
n. - sauce au chili

Deutsch (German)
1.
n. - Maulwurf

2.
n. - Leberfleck, Muttermal

3.
n. - Mole, Hafendamm

4.
n. - (Chem.) Mol, Grammmoleküle

5.
n. - Mole

6.
n. - mexikanische scharfe Chilisoße

Ελληνική (Greek)
n. - κρεατοελιά, (ζωολ.) τυφλοπόντικας, μόλος, κυματοθραύστης, τεχνητό λιμάνι

Italiano (Italian)
talpa, neo

Português (Portuguese)
n. - sinal congênito na pele (m), toupeira (f) Zool., quebra-mar (f)

Русский (Russian)
родинка, крот, дамба, моль, агент, внедрившийся в иностранную разведку

Español (Spanish)
1.
n. - topo

2.
n. - lunar

3.
n. - rompeolas, dársena, malecón

4.
n. - mol

5.
n. - fibroma

6.
n. - salsa de chile picante

Svenska (Swedish)
n. - (födelse)märke, vågbrytare, mullvad, grammolekyl

中文（简体）(Chinese (Simplified))
1. 鼹鼠, 钱鼠, 隧道全断面掘进机, 长期潜伏的间谍

2. 痣

3. 胎块

4. 防波堤

5. 摩尔, 克分子

6. 鼹鼠, 钱鼠, 隧道全断面掘进机, 长期潜伏的间谍

中文（繁體）(Chinese (Traditional))
1.
n. - 鼴鼠, 錢鼠, 隧道全斷面掘進機, 長期潛伏的間諜

2.
n. - 摩爾, 克分子

3.
n. - 痣

4.
n. - 胎塊

5.
n. - 防波堤

6.
n. - 鼴鼠, 錢鼠, 隧道全斷面掘進機, 長期潛伏的間諜

한국어 (Korean)
1.
n. - 두더지

2.
n. - (피부의) 검은 점

3.
n. - 방파제

4.
n. - (화학의) 몰

5.
n. - 자궁조직의 비정상적인 덩어리

6.
n. - 매운 칠리소스

日本語 (Japanese)
n. - モグラ, ほくろ, 防波堤

العربيه (Arabic)
‏(الاسم) شامه, خال‏

עברית (Hebrew)
n. - ‮חפרפרת, חולד‬
n. - ‮שומה, בהרת‬
n. - ‮מזח, שובר-גלים‬
n. - ‮יחידת-כמות תקנית של חומר‬
n. - ‮כמות לא רגילה של רקמה ברחם‬
n. - ‮סוג של רטוב צ'ילי‬

If you are unable to view some languages clearly, click here.

To select your translation preferences click here.


 
 

 

Copyrights:

Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.  Read more
Sci-Tech Encyclopedia. McGraw-Hill Encyclopedia of Science and Technology. Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved.  Read more
Computer Desktop Encyclopedia. THIS COPYRIGHTED DEFINITION IS FOR PERSONAL USE ONLY.
All other reproduction is strictly prohibited without permission from the publisher.
© 1981-2009 Computer Language Company Inc.  All rights reserved.  Read more
Measures and Units. A Dictionary of Weights, Measures, and Units. Copyright © Donald Fenna 2002, 2004. All rights reserved.  Read more
Britannica Concise Encyclopedia. Britannica Concise Encyclopedia. © 2006 Encyclopædia Britannica, Inc. All rights reserved.  Read more
Sports Science and Medicine. The Oxford Dictionary of Sports Science & Medicine. Copyright © Michael Kent 1998, 2006, 2007. All rights reserved.  Read more
Columbia Encyclopedia. The Columbia Electronic Encyclopedia, Sixth Edition Copyright © 2003, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/.  Read more
Science Q&A. The Handy Science Answer Book. 2003 ©Visible Ink Press. All rights reserved.  Read more
Obscure Words. © 2008 by Michael A. Fischer http://home.comcast.net/~wwftd.  Read more
Wikipedia. This article is licensed under the Creative Commons Attribution/Share-Alike License. It uses material from the Wikipedia article "Mole (unit)".  Read more
Translations. Copyright © 2007, WizCom Technologies Ltd. All rights reserved.  Read more