分子量、分子質量

関: molecular weight、Mr、Mw

WordNet

join together into a mass or collect or form a mass; "Crowds were massing outside the palace"
the property of a body that causes it to have weight in a gravitational field
a body of matter without definite shape; "a huge ice mass"
an ill-structured collection of similar things (objects or people)
relating to simple or elementary organization; "proceed by more and more detailed analysis to the molecular facts of perception"--G.A. Miller
relating to or produced by or consisting of molecules; "molecular structure"; "molecular oxygen"; "molecular weight is the sum of all the atoms in a molecule"
(Roman Catholic Church and Protestant Churches) the celebration of the Eucharist
a musical setting for a Mass; "they played a Mass composed by Beethoven"
a sequence of prayers constituting the Christian Eucharistic rite; "the priest said Mass"
informal terms for a mother (同)mama, mamma, mom, momma, mommy, mammy, mum, mummy

PrepTutorEJDIC

〈C〉(一定の形をもたない物に用いて)…の)『固まり』,集まり《+『of』+『名』》 / 〈C〉『多数』,多量(の…)《+『of』+『名』》 / 〈C〉《the ~》『大部分』(の…),(…の)主要部《+『of』+『名』》 / 〈U〉(物体の)大きさ,かさ / 《the masses》『一般大衆』,庶民 / 〈U〉質量(物体の基本的性質を表す量) / 〈人・物〉‘を'集める,一団にする / 〈人・物が〉一かたまりになる,一団となる / 大衆の,一般に付及した / 大規模な
分子の,分子による
《M-》《話》おかあちゃん(mamma)

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2013/09/11 10:31:43」(JST)

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Assuming hydrogen and oxygen are standard weights in this image (as opposed to deuterium oxide) the molecular mass should be 18.01528 u.

The molecular mass (m_a) is the mass of a molecule.

Units[edit source | edit]

The SI unit of mass is kg. However, for molecular mass more commonly the atomic mass unit (symbol u or Da) is used. For example, the molecular mass of water is approximately

m_a(H₂O) ≈ 18 u ≈ 3×10⁻²⁶ kg.

Related quantities[edit source | edit]

Molecular weight[edit source | edit]

Molecular mass is sometimes called molecular weight. However, this is incorrect because mass and weight are different (see Mass versus weight). Another possible source of confusion is that some older textbooks use the term "molecular weight" to mean the molar mass.^[1] This terminology is not used in modern literature.^{[citation needed]}

Relative molecular mass[edit source | edit]

The numerical value of the absolute molecular mass expressed in unified atomic mass units is equivalent to the dimensionless relative molecular mass M_r^[2]

M_r (H₂O) ≈ 18.

Thus, it is incorrect to express relative molecular mass (molecular weight) in daltons (Da).

Molar mass[edit source | edit]

Main article: molar mass

The molar mass of a substance is the mass of 1 mol (the SI unit for the basis SI quantity amount of substance, having the symbol n) of the substance. This has a numerical value which is the average molecular mass of the molecules in the substance multiplied by Avogadro's constant (approximately 6.022×10²³). The most common units of molar mass are g/mol because in those units the numerical value equals the average molecular mass in units of u.

Many chemists use molecular mass as a synonym of molar mass,^[3] differing only in units (see average molecular mass below). A stricter interpretation does not equate the two, as the mass of a single molecule is not the same as the average of an ensemble. Because a mole of molecules may contain a variety of molecular masses due to natural isotopes, the average mass is usually not identical to the mass of any single molecule. The actual numerical difference can be very small when considering small molecules and the molecular mass of the most common isotopomer in which case the error only matters to physicists and a small subset of highly specialized chemists; however it is always more correct, accurate and consistent to use molar mass in any bulk stoichiometric calculations. The size of this error becomes much larger when considering larger molecules or less abundant isotopomers. The molecular mass of a molecule which happens to contain heavier isotopes than the average molecule in the sample can differ from the molar mass by several mass units.

Average molecular mass[edit source | edit]

The average molecular mass is another variation on the use of the term molecular mass. The average molecular mass is the abundance weighted mean (average) of the molecular masses in a sample. This is often closer to what is meant when "molecular mass" and "molar mass" are used synonymously and may have derived from shortening of this term. The average molecular mass and the molar mass of a particular substance in a particular sample are in fact numerically identical and may be inter-converted by Avogadro's constant. It should be noted, however, that the molar mass is almost always a computed figure derived from the Relative atomic masss, whereas the average molecular mass, in fields that need the term, is often a measured figure specific to a sample. Therefore, they often vary since one is theoretical and the other is experimental. Specific samples may vary significantly from the expected isotopic composition due to real deviations from earth's average isotopic abundances.

Computation[edit source | edit]

The molecular mass can be calculated as the sum of the individual isotopic masses (as found in a table of isotopes) of all the atoms in any molecule. This is possible because molecules are created by chemical reactions which, unlike nuclear reactions, have very small binding energies compared to the rest mass of the atoms ( 10⁻⁹) and therefore create a negligible mass defect. The use of average atomic masses derived from the standard atomic masses found on a standard periodic table will result in an average molecular mass, whereas the use of isotopic masses will result in a molecular mass consistent with the strict interpretation of the definition, i.e. that of a single molecule. However, any given molecule may contain any given combination of isotopes, so there may be multiple molecular masses for each chemical compound.

Measurement[edit source | edit]

The molecular mass can also be measured directly using mass spectrometry. In mass spectrometry, the molecular mass of a small molecule is usually reported as the monoisotopic mass, that is, the mass of the molecule containing only the most common isotope of each element. Note that this also differs subtly from the molecular mass in that the choice of isotopes is defined and thus is a single specific molecular mass of the many possible. The masses used to compute the monoisotopic molecular mass are found on a table of isotopic masses and are not found on a typical periodic table. The average molecular mass is often used for larger molecules since molecules with many atoms are unlikely to be composed exclusively of the most abundant isotope of each element. A theoretical average molecular mass can be calculated using the relative atomic masses found on a typical periodic table, since there is likely to be a statistical distribution of atoms representing the isotopes throughout the molecule. This however may differ from the true average molecular mass of the sample due to natural (or artificial) variations in the isotopic distributions.

The basis for determination of molecular mass according to the Staudinger method (since replaced by the more general Mark-Houwink equation^[4]) is the fact that relative viscosity of suspensions depends on volumetric proportion of solid particles.

There are several companies that manufacture accurate instruments for determining absolute molecular mass quickly and easily. These companies include Brookhaven Instruments, Malvern Instruments, and Horiba

Isotopic considerations[edit source | edit]

The average atomic mass of natural hydrogen is 1.00794 u and that of natural oxygen is 15.9994 u; therefore, the molecular mass of natural water with formula H₂O is (2 × 1.00794 u) + 15.9994 u = 18.01528 u. Therefore, one mole of water has a mass of 18.01528 grams. However, the exact mass of hydrogen-1 (the most common hydrogen isotope) is 1.00783, and the exact mass of oxygen-16 (the most common oxygen isotope) is 15.9949, so the mass of the most common molecule of water is 18.01056 u. The difference of 0.00472 u or 0.03% comes from the fact that natural water contain traces of water molecules containing, oxygen-17, oxygen-18 or hydrogen-2 (Deuterium) atoms. Although this difference is trivial in bulk chemistry calculations, it can result in complete failure in situations where the behavior of individual molecules matters, such as in mass spectrometry and particle physics (where the mixture of isotopes does not act as an average).

There are also situations where the isotopic distributions are not typical such as with heavy water used in some nuclear reactors which is artificially enriched with Deuterium. In these cases the computed values of molar mass and average molecular mass, which are ultimately derived from the relative atomic masses, will not be the same as the actual molar mass or average molecular mass of the sample. In this case the mass of deuterium is 2.0136 u and the average molecular mass of this water (assuming 100% deuterium enrichment) is (2 × 2.0136 u) + 15.9994 u = 20.0266 u. This is a very large difference of ~11% error from the expected average molecular mass based on the standard atomic masses. Furthermore the most abundant molecular mass is actually slightly less than the average molecular mass since oxygen-16 is still the most common. (2 × 2.0136 u) + 15.9949 u = 20.0221 u. Although this is an extreme artificial example, natural variation in isotopic distributions do occur and are measurable. For example, the atomic mass of lithium as found by isotopic analysis of 39 lithium reagents from several manufacturers varied from 6.939 to 6.996.^[5]

References[edit source | edit]

^ For instance, seeHill, Nora E. et al. (1969). Dielectric properties and molecular behaviour. London: Van Nostrand Reinhold. ISBN 0442034113.
^ http://goldbook.iupac.org/R05271.html
^ http://www.mrcoulter.com/REG_LECTURES/09formula.pdf
^ Mark-Houwink equation
^ http://pubs.acs.org/cgi-bin/abstract.cgi/ancham/1997/69/i19/abs/ac9704669.html

External links[edit source | edit]

A Free Android application for molecular and reciprocal weight calculation of any chemical formula
Stoichiometry Add-In for Microsoft Excel for calculation of molecular weights, reaction coefficients and stoichiometry.

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English Journal

Dual antiplatelet treatment in patients candidates for abdominal surgery.

Illuminati G, Ceccanei G, A Pacilè M, Pizzardi G, Palumbo P, Vietri F.AbstractWith the increasing diffusion of percutaneous interventions (PCI), surgeons are often faced with the problem of operating on patients under dual antiplatelet treatment. Replacing dual antiplatelet regiment with low molecular weight heparin may expose to the abrupt thrombosis of coronary stent and massive myocardial infarction. The purpose of this study was to test the hypothesis that abdominal operations can be safely performed under dual antiplatelet treatment. Eleven patients underwent 5 colectomies, 3 nefrectomies, 2 gastrectomies and 1 hysterectomy under aspirin and plavix without any significant perioperative hemorrhage. These preliminary results show that abdominal operations can be safely performed under dual antiplatelet regimen.
Annali italiani di chirurgia.Ann Ital Chir.2014;83:291-4.
With the increasing diffusion of percutaneous interventions (PCI), surgeons are often faced with the problem of operating on patients under dual antiplatelet treatment. Replacing dual antiplatelet regiment with low molecular weight heparin may expose to the abrupt thrombosis of coronary stent and ma
PMID 23103787

Evolution of colour and phenolic compounds during Garnacha Tintorera grape raisining.

Figueiredo-González M, Cancho-Grande B, Simal-Gándara J.SourceNutrition and Bromatology Group, Analytical and Food Chemistry Department, Faculty of Food Science and Technology, University of Vigo, Ourense Campus, E-32004 Ourense, Spain.
Food chemistry.Food Chem.2013 Dec 1;141(3):3230-40. doi: 10.1016/j.foodchem.2013.05.142. Epub 2013 Jun 10.
The off-vine drying is one of the most important steps in the production of a high quality naturally sweet wine. However, only few studies have analyzed the changes in colour and phenolic compounds of the grapes throughout the process. In this work, UV/Vis spectrophotometry and HPLC/DAD-ESI/MS were
PMID 23871082

Determination and identification of hydrophilic and hydrophobic arsenic species in methanol extract of fresh cod liver by RP-HPLC with simultaneous ICP-MS and ESI-Q-TOF-MS detection.

Arroyo-Abad U, Lischka S, Piechotta C, Mattusch J, Reemtsma T.SourceUFZ - Helmholtz Centre for Environmental Research, Department of Analytical Chemistry, Permoserstrasse 15, 04318 Leipzig, Germany.
Food chemistry.Food Chem.2013 Dec 1;141(3):3093-102. doi: 10.1016/j.foodchem.2013.05.152. Epub 2013 Jun 10.
The present study was focused on the determination and identification of arsenic species in methanolic extracts of cod liver. Arsenic species were fractionated and the fractions analysed by RP-HPLC-ICP-MS coupled with ESI-Q-TOF-MS. The total concentration of arsenic in the fresh cod liver was analys
PMID 23871064

Japanese Journal

Surface Assisted Laser Desorption Ionization Mass Spectrometry (SALDI-MS) of Low-molecular-weight Medicines and Toxic Materials Using Commercial TiO2 Nanoparticles

Bulletin of the Chemical Society of Japan advpub(0), 2016
NAID 130005112199

Fragment ions produced from hexamethyldisilane in a Freeman-type ion source

Jpn. J. Appl. Phys. 54(10), 108001, 2015-09-17
NAID 150000111391

Laboratory photochemical processing of aqueous aerosols : formation and degradation of dicarboxylic acids, oxocarboxylic acids and alpha-dicarbonyls

Atmospheric chemistry and physics 15(14), 7999-8012, 2015-09-17
NAID 120005651861

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リンク元	「分子量」「Mr」「Mw」「molecular weight」「分子質量」
拡張検索	「low molecular mass」
関連記事	「mass」「molecular」