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 C4.  MOLAR MASS: THE MASS PER UNIT AMOUNT OF SUBSTANCE 

This term applies to ALL entities including elements in the atomic state.

MOLAR MASS (M) is defined as the mass (m) per unit amount of substance (n),
i.e., per mole, e.g., M (U) = 238 g/mol.

It is the bridging quantity that connects the pair of physical quantities amount of substance and mass:

M =

n

m

What values can we reasonably expect to be dealing with for molar masses ?

  • atoms of naturally occurring elements: 1 – 238 g/mol

  • 'simple' chemical compounds: 5.0 – 1000 g/mol

  • for polymers, proteins, DNA fragments, & similar: 1001 – 5 000 000 g/mol

Molar mass, like density, is an intrinsic - characteristic - property of a substance.

Since molar mass can often be measured directly by mass spectrometry to a precision of a few parts per million, this is sufficiently precise to determine a molecular formula.

Suggest the identity of the compound whose molar mass, M = 5.0 g / mol.

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