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The molar mass is an average of many instances of the compound, which often vary in mass due to the presence of isotopes. Most commonly, the molar mass is computed from the standard atomic weights and is thus a terrestrial average and a function of the relative abundance of the isotopes of the constituent atoms on Earth. The molar mass is ...
The exact mass of an isotopic species (more appropriately, the calculated exact mass [9]) is obtained by summing the masses of the individual isotopes of the molecule. For example, the exact mass of water containing two hydrogen-1 ( 1 H) and one oxygen-16 ( 16 O) is 1.0078 + 1.0078 + 15.9949 = 18.0105 Da.
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 molar mass is ...
Assuming the unknown compound behaves as an ideal gas, the number of moles of the unknown compound, n, can be determined by using the ideal gas law, p V = n R T {\displaystyle pV=nRT\,} where the pressure, p , is the atmospheric pressure , V is the measured volume of the vessel, T is the absolute temperature of the hot bath, and R is the gas ...
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.
Nominal mass is a term used in high level mass spectrometric discussions, it can be calculated using the mass number of the most abundant isotope of each atom, without regard for the mass defect. For example, when calculating the nominal mass of a molecule of nitrogen (N 2) and ethylene (C 2 H 4) it comes out as. N 2 (2*14)= 28 Da C 2 H 4
The Kendrick mass is defined by setting the mass of a chosen molecular fragment, typically CH 2, to an integer value in u (unified atomic mass unit). It is different from the IUPAC definition, which is based on setting the mass of 12 C isotope to exactly 12 u.
Thus, the atomic mass of a carbon-12 atom is 12 Da by definition, but the relative isotopic mass of a carbon-12 atom is simply 12. The sum of relative isotopic masses of all atoms in a molecule is the relative molecular mass. The atomic mass of an isotope and the relative isotopic mass refers to a certain specific isotope of an element.