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When expressed in percent, it is known as the mole percent or molar percentage (unit symbol %, sometimes "mol%", equivalent to cmol/mol for 10-2). The mole fraction is called amount fraction by the International Union of Pure and Applied Chemistry (IUPAC) [ 1 ] and amount-of-substance fraction by the U.S. National Institute of Standards and ...
This formulation has appealing properties such as no change being equal to zero, a 100% increase is equal to 1, and a 100% decrease is equal to −1. However, verbally referring to a doubling as a one-fold change and tripling as a two-fold change is counter-intuitive, and so this formulation is rarely used. Volcano plot showing metabolomic data ...
A closely related concept is the atomic percent (or at.%), which gives the percentage of one kind of atom relative to the total number of atoms. [1] The molecular equivalents of these concepts are the molar fraction , or molar percent .
For example, we might want to calculate the relative change of −10 to −6. The above formula gives (−6) − (−10) / −10 = 4 / −10 = −0.4, indicating a decrease, yet in fact the reading increased. Measures of relative change are unitless numbers expressed as a fraction. Corresponding values of percent change would be ...
The derived quantity relative molecular mass is the unitless ratio of the mass of a molecule to the atomic mass constant (which is equal to one dalton). [ 2 ] The molecular mass and relative molecular mass are distinct from but related to the molar mass .
Graham's law can also be used to find the approximate molecular weight of a gas if one gas is a known species, and if there is a specific ratio between the rates of two gases (such as in the previous example). The equation can be solved for the unknown molecular weight.
Molecular weight (M.W.) (for molecular compounds) and formula weight (F.W.) (for non-molecular compounds), are older terms for what is now more correctly called the relative molar mass (M r). [8] This is a dimensionless quantity (i.e., a pure number, without units) equal to the molar mass divided by the molar mass constant .
The mass-average molecular mass, M w, is also related to the fractional monomer conversion, p, in step-growth polymerization (for the simplest case of linear polymers formed from two monomers in equimolar quantities) as per Carothers' equation: ¯ = + ¯ = (+), where M o is the molecular mass of the repeating unit.