molar mass

Meaning

1. 1nouncountable or uncountabletechnicalchemistry

   The mass of one mole of a substance, equal to the sum of the atomic masses of its atoms, expressed in grams per mole.

   Grammar: Often used with the definite article: 'the molar mass of water'. Can be countable when referring to different substances: 'different molar masses'.

   Patterns

   • the molar mass of something
   • calculate the molar mass
   • molar mass in g/mol

   The molar mass of water is about 18 grams per mole.

   To find the number of moles, divide the mass of the sample by its molar mass.

   Chemists use molar mass to convert between grams and moles in stoichiometry problems.

Common combinations

calculate the molar mass

You need to calculate the molar mass of the compound before you can find the number of moles.

molar mass of a substance

The molar mass of a substance is the mass of one mole of its particles.

molar mass in grams per mole

Express the molar mass in grams per mole for these calculations.

average molar mass

For polymers, we often talk about the average molar mass.

Synonyms and how they differ

molecular weight

Often used interchangeably with molar mass in everyday chemistry, but strictly molecular weight is a dimensionless quantity, while molar mass has units of g/mol.

molecular mass

Similar concept but measured in atomic mass units (u), not grams per mole; molar mass is the mass of one mole, molecular mass is the mass of one molecule.

Word family

mole noun

The SI unit of amount of substance, equal to Avogadro's number of particles.

molar adjective

Relating to a mole, as in molar concentration or molar mass.

molarity noun

The concentration of a solution expressed as moles of solute per liter of solution.

Commonly confused: molar mass or molecular mass? molar mass or atomic mass?

Practice

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