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Historically, the mole was defined as the amount of substance in 12 grams of the carbon-12 isotope.As a consequence, the mass of one mole of a chemical compound, in grams, is numerically equal (for all practical purposes) to the mass of one molecule or formula unit of the compound, in daltons, and the molar mass of an isotope in grams per mole is approximately equal to the mass number ...
The molar mass is defined as the mass of a given substance divided by the amount of the substance, and is expressed in grams per mol (g/mol). That makes the molar mass an average of many particles or molecules (potentially containing different isotopes ), and the molecular mass the mass of one specific particle or molecule.
The number of particles in a mole is the Avogadro number (symbol N 0) and the numerical value of the Avogadro constant (symbol N A) expressed in mol −1. [1] The SI value of the mole was chosen on the basis of the historical definition of the mole as the amount of substance that corresponds to the number of atoms in 12 grams of 12 C, [1] which ...
The molar mass of atoms of an element is given by the relative atomic mass of the element multiplied by the molar mass constant, M u ≈ 1.000 000 × 10 −3 kg/mol ≈ 1 g/mol. For normal samples from Earth with typical isotope composition, the atomic weight can be approximated by the standard atomic weight [ 2 ] or the conventional atomic weight.
Mass fraction can also be expressed, with a denominator of 100, as percentage by mass (in commercial contexts often called percentage by weight, abbreviated wt.% or % w/w; see mass versus weight). It is one way of expressing the composition of a mixture in a dimensionless size ; mole fraction (percentage by moles , mol%) and volume fraction ...
Atomic number Element Molar mass Formal standard atomic weight s.a.w., formal short Note Z calculated; g·mol −1 A r, standard [2] A r, abridged and conventional [2]; C 9 H 8 O 4: 180.159 g·mol −1
The concentration of pure osmium tetroxide (molar mass = 254.23 g/mol) is c(OsO 4) = 5.1 kg/L / 254.23 g/mol = 20.1 mol/L. A typical protein in bacteria, such as E. coli, may have about 60 copies, and the volume of a bacterium is about 10 −15 L. Thus, the number concentration C is C = 60 / (10 −15 L) = 6 × 10 16 L −1. The molar ...
The molar mass constant, usually denoted by M u, is a physical constant defined as one twelfth of the molar mass of carbon-12: M u = M(12 C)/12. [1] The molar mass of an element or compound is its relative atomic mass (atomic weight) or relative molecular mass (molecular weight or formula weight) multiplied by the molar mass constant.