Chemical Compound Molar Mass, Molecular Weight Calculator. To calculate molar mass of a chemical compound, please enter its chemical formula and click 'Calculate'. Definitions of molecular mass, molecular weight, molar mass and molar weight: Molecular mass (molecular weight) is the mass of one molecule of a substance and is expressed in the unified atomic mass units (u). (1 u is equal to 1/12 the mass.
Not to be confused with or.The molecular mass ( m) is the mass of a given molecule: it is measured in (u or Da). Different molecules of the same compound may have different molecular masses because they contain different of an element. The related quantity relative molecular mass, as defined by, is the ratio of the mass of a molecule to the unified atomic mass unit and is unitless. The molecular mass and relative molecular mass are distinct from but related to the. The molar mass is defined as the mass of a given substance divided by the and is expressed in g/mol. The molar mass is usually the more appropriate figure when dealing with macroscopic (weigh-able) quantities of a substance.The definition of molecular weight is most authoritatively synonymous with molecular mass; however, in common practice, it is also highly variable as are the units used in conjunction with it.
Many common preparatory sources use g/mol and effectively define it as a synonym of molar mass, while more authoritative sources use Da or u and align its definition more closely with the molecular mass. Even when the molecular weight is used with the units Da or u, it is frequently as a weighted average similar to the molar mass but with different units.
In molecular biology, the weight of macromolecules is referred to as their molecular weight and is expressed in kDa, although the numerical value is often approximate and representative of an average.The terms molecular mass, molecular weight, and molar mass are often used interchangeably in areas of science where distinguishing between them is unhelpful. In other areas of science, the distinction is crucial. The molecular mass is more commonly used when referring to the mass of a single or specific well-defined molecule and less commonly than molecular weight when referring to a weighted average of a sample. Prior to the quantities expressed in unified atomic mass units (u or Da) were by definition numerically equivalent to otherwise identical quantities expressed in the units g/mol and were thus strictly numerically interchangeable. After the May 20th, 2019 redefinition of units, this relationship is only nearly equivalent.The molecular mass of small to medium size molecules, measured by mass spectrometry, can be used to determine the of elements in the molecule. The molecular masses of macromolecules, such as proteins, can also be determined by mass spectrometry; however, methods based on and light-scattering are also used to determine molecular mass when or mass spectrometric data are not available. Contents.Calculation Molecular masses are calculated from the of each present in the molecule, while molar masses are calculated from the of each.
The standard atomic weight takes into account the of the element in a given sample (usually assumed to be 'normal'). For example, has a molar mass of 18.0153(3) g/mol, but individual water molecules have molecular masses which range between 18.010 564 6863(15) u ( 1H2 16O) and 22.027 7364(9) u ( 2H2 18O).Atomic and molecular masses are usually reported in which is defined relative to the mass of the 12C (carbon 12), which by definition is equal to 12 u. For example, the molar mass and molecular mass of, whose molecular formula is CH 4, are calculated respectively as follows:Molar mass or molecular weight of CH 4Standard atomic weightNumberTotal molar mass (g/mol)or molecular weight (Da or g/mol)C12.011112.011H1.00844.032CH 416.043Molecular mass of 12C 1H 4Nuclide massNumberTotal molecular mass (Da or u)2.001H1.007CH 416.0313The more formally defined term is 'relative molecular mass'. Relative atomic and molecular mass values as defined are. However, the adjective 'relative' is omitted in practice as it is universally assumed that atomic and molecular masses are relative to the mass of 12C.
Additionally, the 'unit' is used in common practice. The mass of 1 of substance is designated as. By definition, the molar mass has the units of per.In the example above the standard atomic weight of carbon is 12.011 g/mol, not 12.00 g/mol. This is because naturally occurring carbon is a mixture of the 12C, 13C and 14C which have masses of 12 u, 13.003355 u and 14.003242 u respectively. Moreover, the proportion of the isotopes varies between samples, so 12.011 g/mol is an average value across different places on earth. By contrast, there is less variation in naturally occurring hydrogen so the standard atomic weight has less variance. The precision of the molar mass is by the highest variance standard atomic weight, in this example that of carbon.
This uncertainty is not the same as the uncertainty in the molecular mass, which reflects variance (error) in measurement not the natural variance in isotopic abundances across the globe. In high-resolution the mass isotopomers 12C 1H 4 and 13C 1H 4 are observed as distinct molecules, with molecular masses of approximately 16.031 and 17.035, respectively. The intensity of the mass-spectrometry peaks is proportional to the isotopic abundances in the molecular species. 12C 2H 1H 3 can also be observed with molecular mass of 17.Determination Mass spectrometry. Main article:In mass spectrometry, the molecular mass of a small molecule is usually reported as the, 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 possibilities. 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 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, the average molecular mass of a sample usually differs substantially from this since a single sample average is not the same as the average of many geographically distributed samples.Hydrodynamic methods To a first approximation, the basis for determination of molecular mass according to is the fact that the of (or ) of macromolecules depends on volumetric proportion of the dispersed particles in a particular solvent. Specifically, the hydrodynamic size as related to molecular mass depends on a conversion factor, describing the shape of a particular molecule. This allows the apparent molecular mass to be described from a range of techniques sensitive to hydrodynamic effects, including, (also known as when the eluent is an organic solvent), and diffusion ordered (DOSY).
The apparent can then be used to approximate molecular mass using a series of macromolecule-specific standards. As this requires calibration, it's frequently described as a 'relative' molecular mass determination method.Static light scattering It is also possible to determine absolute molecular mass directly from light scattering, traditionally using the. This can be accomplished either via classical or via detectors. Molecular masses determined by this method do not require calibration, hence the term 'absolute'.
The only external measurement required is, which describes the change in refractive index with concentration.See also.References. (2006), (PDF) (8th ed.), p. 126, (PDF) from the original on 2017-08-14. Mohr, Peter J.; Taylor, Barry N.; Newell, David B. Cite journal requires journal= Database developed by J. Douma, and S. Kotochigova., Gaithersburg, MD 20899.
Retrieved 2007-10-14. (1980). 52 (10): 2349–84. Paul, Hiemenz C., and Lodge P. Polymer Chemistry. Boca Raton: CRC P, 2007.
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336, 338–339. Johnson Jr., C. 'Diffusion ordered nuclear magnetic resonance spectroscopy: principles and applications'.
34: 203–256. Neufeld, R.; Stalke, D. 6: 3354–3364.External links. for calculation of molecular weights, reaction coefficients and stoichiometry.
The relative atomic mass indicates how many times larger the mass of a given atom is than 1/12 the mass of the 12C carbon isotope. Relative atomic mass is a dimensionless number. An element generally consists of several isotopes of differing atomic mass. The relative atomic masses listed here represent average values of the naturally occurring isotopic mixture on the Earth and they are expressed with five.The Hill system (or Hill notation) is a standard way of writing the formula for any chemical compound. With the Hill notation, the number of carbon atoms in a molecule is indicated first, the number of hydrogen atoms next, and then the number of all other chemical elements subsequently, in alphabetical order.
When the formula contains no carbon, all the elements, including hydrogen, are listed alphabetically. Bibliography:. J. Meija et al.,. 88, 265-291 (2016).