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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.
The molar mass of a substance depends not only on its molecular formula, but also on the distribution of isotopes of each chemical element present in it. For example, the molar mass of calcium-40 is 39.962 590 98 (22) g/mol, whereas the molar mass of calcium-42 is 41.958 618 01 (27) g/mol, and of calcium with the normal isotopic mix is 40.078(4 ...
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). That makes the molar mass an average of many particles or molecules (potentially containing different ...
The molar mass constant is important in writing dimensionally correct equations. [4] While one may informally say "the molar mass M of an element has the same numerical value as its atomic weight A ", the atomic weight (relative atomic mass) A is a dimensionless quantity, whereas the molar mass M has the SI base unit of kilogram per mole but is ...
The mass average molar mass (often loosely termed weight average molar mass) is another way of describing the molar mass of a polymer. Some properties are dependent on molecular size, so a larger molecule will have a larger contribution than a smaller molecule.
Molecular mass and molar mass mean what one expect today: respectively the mass of a single molecule (in g with a value near 10-27 g) and the mass of a mole (with a value of 1 g or more). However molecular weight is still used as an old-fashioned term normally given in g per mole, so the values are really molar mass although the term "molecular ...
A uniform polymer (often referred to as a monodisperse polymer) is composed of molecules of the same mass. [5] Nearly all natural polymers are uniform. [6] Synthetic near-uniform polymer chains can be made by processes such as anionic polymerization, a method using an anionic catalyst to produce chains that are similar in length.
The unit of quantity is mol (defined as containing Avogadro number molecules), the unit of mass is kg, so the unit of molar mass is kg/mol (for instance 0.01802 kg/mol for water.) The molar mass of any substance can be obtained multiplying the relative molecular mass (often still called molecular weight and abbreviated as MW) by 0.001 kg/mol.