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In chemistry, the molar mass (M) (sometimes called molecular weight or formula weight, but see related quantities for usage) of a chemical compound is defined as the ratio between the mass and the amount of substance (measured in moles) of any sample of the compound. [1] The molar mass is a bulk, not molecular, property of a substance.
H + 3 is one of the most abundant ions in the universe, and it plays a notable role in the chemistry of the interstellar medium. [101] Neutral triatomic hydrogen H 3 can exist only in an excited form and is unstable. [102] By contrast, the positive hydrogen molecular ion (H + 2) is a rare molecule in the universe.
Equivalent weights may be calculated from molar masses if the chemistry of the substance is well known: sulfuric acid has a molar mass of 98.078(5) g mol −1, and supplies two moles of hydrogen ions per mole of sulfuric acid, so its equivalent weight is 98.078(5) g mol −1 /2 eq mol −1 = 49.039(3) g eq −1.
The molecular mass and relative molecular mass are distinct from but related to the molar mass. 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).
Molar mass: 18.01528(33) g/mol ... In a water molecule, the hydrogen atoms form a 104.5° angle with the oxygen atom. ... the gram was defined in France to be equal ...
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 reduced mass of the system in these equations is close to the mass of a single electron, but differs from it by a small amount about equal to the ratio of mass of the electron to the nucleus. For 1 H, this amount is about 1837 / 1836 , or 1.000545, and for 2 H it is even smaller: 3671 / 3670 , or 1.0002725.
Because a dalton, a unit commonly used to measure atomic mass, is exactly 1/12 of the mass of a carbon-12 atom, this definition of the mole entailed that the mass of one mole of a compound or element in grams was numerically equal to the average mass of one molecule or atom of the substance in daltons, and that the number of daltons in a gram ...