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Molar mass is defined as the mass of one mole of a substance. The molar mass of a compound is equal to the sum of the relative atomic masses of its constituents expressed in g mol-1.
The molecular weight is very commonly used as a synonym of molar mass, particularly for molecular compounds; however, the most authoritative sources define it differently (see molecular mass).
The formula weight is a synonym of molar mass that is frequently used for non-molecular compounds, such as ionic salts.
- relative atomic mass of one hydrogen atom = 1.008 u
- molar mass of hydrogen atom = 1.008 g mol-1
- relative molecular mass of glucose = 180 u
- molar mass of glucose = 180 g m
To find the molar mass of a compound:
- Use the chemical formula to determine the number of each type of atom present in the compound.
- Multiply the atomic weight (from the periodic table) of each element by the number of atoms of that element present in the compound.
- Add it all together and put units of grams/mole after the number.
Molar Mass Formula
Molar mass is the mass of one mole of a substance. The mass will be represented in grams while a mole of a substance is defined as 6.02 x 1023 representative particles (Avogadro’s number) of that substance.
Example : Calculate the molar mass of a substance if 0.235 moles has a mass of 45.67 grams.